## ISO/IEC 9899:201x Committee Draft April 12, 2011 N1570

### ABSTRACT. [Abstract]

    (Cover sheet to be provided by ISO Secretariat.)

    This International Standard specifies the form and establishes the interpretation of
    programs expressed in the programming language C. Its purpose is to promote
    portability, reliability, maintainability, and efficient execution of C language programs on
    a variety of computing systems.

    Clauses are included that detail the C language itself and the contents of the C language
    execution library. Annexes summarize aspects of both of them, and enumerate factors
    that influence the portability of C programs.

    Although this International Standard is intended to guide knowledgeable C language
    programmers as well as implementors of C language translation systems, the document
    itself is not designed to serve as a tutorial.

    Recipients of this draft are invited to submit, with their comments, notification of any
    relevant patent rights of which they are aware and to provide supporting documentation.

    Changes from the previous draft (N1539) are indicated by ‘‘diff marks’’ in the right
    margin: deleted text is marked with ‘‘∗’’, new or changed text with ‘‘ ’’.

### CONTENTS. [Contents]

    Foreword
    Introduction
    1. Scope
    2. Normative references
    3. Terms, definitions, and symbols
    4. Conformance
    5. Environment
       5.1 Conceptual models
            5.1.1  Translation environment
            5.1.2  Execution environments
       5.2 Environmental considerations
            5.2.1  Character sets
            5.2.2  Character display semantics
            5.2.3  Signals and interrupts
            5.2.4  Environmental limits
    6. Language
       6.1 Notation
       6.2 Concepts
            6.2.1   Scopes of identifiers
            6.2.2   Linkages of identifiers
            6.2.3   Name spaces of identifiers
            6.2.4   Storage durations of objects
            6.2.5   Types
            6.2.6   Representations of types
            6.2.7   Compatible type and composite type
            6.2.8   Alignment of objects
       6.3 Conversions
            6.3.1   Arithmetic operands
            6.3.2   Other operands
       6.4 Lexical elements
            6.4.1   Keywords
            6.4.2   Identifiers
            6.4.3   Universal character names
            6.4.4   Constants
            6.4.5   String literals
            6.4.6   Punctuators
            6.4.7   Header names
            6.4.8   Preprocessing numbers
            6.4.9   Comments
    6.5  Expressions
         6.5.1   Primary expressions
         6.5.2   Postfix operators
         6.5.3   Unary operators
         6.5.4   Cast operators
         6.5.5   Multiplicative operators
         6.5.6   Additive operators
         6.5.7   Bitwise shift operators
         6.5.8   Relational operators
         6.5.9   Equality operators
         6.5.10 Bitwise AND operator
         6.5.11 Bitwise exclusive OR operator
         6.5.12 Bitwise inclusive OR operator
         6.5.13 Logical AND operator
         6.5.14 Logical OR operator
         6.5.15 Conditional operator
         6.5.16 Assignment operators
         6.5.17 Comma operator
    6.6 Constant expressions
    6.7 Declarations
         6.7.1   Storage-class specifiers
         6.7.2   Type specifiers
         6.7.3   Type qualifiers
         6.7.4   Function specifiers
         6.7.5   Alignment specifier
         6.7.6   Declarators
         6.7.7   Type names
         6.7.8   Type definitions
         6.7.9   Initialization
         6.7.10 Static assertions
    6.8 Statements and blocks
         6.8.1   Labeled statements
         6.8.2   Compound statement
         6.8.3   Expression and null statements
         6.8.4   Selection statements
         6.8.5   Iteration statements
         6.8.6   Jump statements
    6.9 External definitions
         6.9.1   Function definitions
         6.9.2   External object definitions
    6.10 Preprocessing directives
         6.10.1 Conditional inclusion
         6.10.2 Source file inclusion
         6.10.3 Macro replacement
           6.10.4 Line control
           6.10.5 Error directive
           6.10.6 Pragma directive
           6.10.7 Null directive
           6.10.8 Predefined macro names
           6.10.9 Pragma operator
      6.11 Future language directions
           6.11.1 Floating types
           6.11.2 Linkages of identifiers
           6.11.3 External names
           6.11.4 Character escape sequences
           6.11.5 Storage-class specifiers
           6.11.6 Function declarators
           6.11.7 Function definitions
           6.11.8 Pragma directives
           6.11.9 Predefined macro names
    7. Library
       7.1 Introduction
             7.1.1 Definitions of terms
             7.1.2 Standard headers
             7.1.3 Reserved identifiers
             7.1.4 Use of library functions
       7.2 Diagnostics <assert.h>
             7.2.1 Program diagnostics
       7.3 Complex arithmetic <complex.h>
             7.3.1 Introduction
             7.3.2 Conventions
             7.3.3 Branch cuts
             7.3.4 The CX_LIMITED_RANGE pragma
             7.3.5 Trigonometric functions
             7.3.6 Hyperbolic functions
             7.3.7 Exponential and logarithmic functions
             7.3.8 Power and absolute-value functions
             7.3.9 Manipulation functions
       7.4 Character handling <ctype.h>
             7.4.1 Character classification functions
             7.4.2 Character case mapping functions
       7.5 Errors <errno.h>
       7.6 Floating-point environment <fenv.h>
             7.6.1 The FENV_ACCESS pragma
             7.6.2 Floating-point exceptions
             7.6.3 Rounding
             7.6.4 Environment
       7.7 Characteristics of floating types <float.h>
    7.8  Format conversion of integer types <inttypes.h>
         7.8.1    Macros for format specifiers
         7.8.2    Functions for greatest-width integer types
    7.9 Alternative spellings <iso646.h>
    7.10 Sizes of integer types <limits.h>
    7.11 Localization <locale.h>
         7.11.1 Locale control
         7.11.2 Numeric formatting convention inquiry
    7.12 Mathematics <math.h>
         7.12.1 Treatment of error conditions
         7.12.2 The FP_CONTRACT pragma
         7.12.3 Classification macros
         7.12.4 Trigonometric functions
         7.12.5 Hyperbolic functions
         7.12.6 Exponential and logarithmic functions
         7.12.7 Power and absolute-value functions
         7.12.8 Error and gamma functions
         7.12.9 Nearest integer functions
         7.12.10 Remainder functions
         7.12.11 Manipulation functions
         7.12.12 Maximum, minimum, and positive difference functions
         7.12.13 Floating multiply-add
         7.12.14 Comparison macros
    7.13 Nonlocal jumps <setjmp.h>
         7.13.1 Save calling environment
         7.13.2 Restore calling environment
    7.14 Signal handling <signal.h>
         7.14.1 Specify signal handling
         7.14.2 Send signal
    7.15 Alignment <stdalign.h>
    7.16 Variable arguments <stdarg.h>
         7.16.1 Variable argument list access macros
    7.17 Atomics <stdatomic.h>
         7.17.1 Introduction
         7.17.2 Initialization
         7.17.3 Order and consistency
         7.17.4 Fences
         7.17.5 Lock-free property
         7.17.6 Atomic integer types
         7.17.7 Operations on atomic types
         7.17.8 Atomic flag type and operations
    7.18 Boolean type and values <stdbool.h>
    7.19 Common definitions <stddef.h>
    7.20 Integer types <stdint.h>
         7.20.1 Integer types
         7.20.2 Limits of specified-width integer types
         7.20.3 Limits of other integer types
         7.20.4 Macros for integer constants
    7.21 Input/output <stdio.h>
         7.21.1 Introduction
         7.21.2 Streams
         7.21.3 Files
         7.21.4 Operations on files
         7.21.5 File access functions
         7.21.6 Formatted input/output functions
         7.21.7 Character input/output functions
         7.21.8 Direct input/output functions
         7.21.9 File positioning functions
         7.21.10 Error-handling functions
    7.22 General utilities <stdlib.h>
         7.22.1 Numeric conversion functions
         7.22.2 Pseudo-random sequence generation functions
         7.22.3 Memory management functions
         7.22.4 Communication with the environment
         7.22.5 Searching and sorting utilities
         7.22.6 Integer arithmetic functions
         7.22.7 Multibyte/wide character conversion functions
         7.22.8 Multibyte/wide string conversion functions
    7.23 _Noreturn <stdnoreturn.h>
    7.24 String handling <string.h>
         7.24.1 String function conventions
         7.24.2 Copying functions
         7.24.3 Concatenation functions
         7.24.4 Comparison functions
         7.24.5 Search functions
         7.24.6 Miscellaneous functions
    7.25 Type-generic math <tgmath.h>
    7.26 Threads <threads.h>
         7.26.1 Introduction
         7.26.2 Initialization functions
         7.26.3 Condition variable functions
         7.26.4 Mutex functions
         7.26.5 Thread functions
         7.26.6 Thread-specific storage functions
    7.27 Date and time <time.h>
         7.27.1 Components of time
         7.27.2 Time manipulation functions
         7.27.3 Time conversion functions
    7.28 Unicode utilities <uchar.h>
         7.28.1 Restartable multibyte/wide character conversion functions
    7.29 Extended multibyte and wide character utilities <wchar.h>
         7.29.1 Introduction
         7.29.2 Formatted wide character input/output functions
         7.29.3 Wide character input/output functions
         7.29.4 General wide string utilities
                  7.29.4.1 Wide string numeric conversion functions
                  7.29.4.2 Wide string copying functions
                  7.29.4.3 Wide string concatenation functions
                  7.29.4.4 Wide string comparison functions
                  7.29.4.5 Wide string search functions
                  7.29.4.6 Miscellaneous functions
         7.29.5 Wide character time conversion functions
         7.29.6 Extended multibyte/wide character conversion utilities
                  7.29.6.1 Single-byte/wide character conversion functions
                  7.29.6.2 Conversion state functions
                  7.29.6.3 Restartable multibyte/wide character conversion
                            functions
                  7.29.6.4 Restartable multibyte/wide string conversion
                            functions
    7.30 Wide character classification and mapping utilities <wctype.h>
         7.30.1 Introduction
         7.30.2 Wide character classification utilities
                  7.30.2.1 Wide character classification functions
                  7.30.2.2 Extensible wide character classification
                            functions
         7.30.3 Wide character case mapping utilities
                  7.30.3.1 Wide character case mapping functions
                  7.30.3.2 Extensible wide character case mapping
                            functions
    7.31 Future library directions
         7.31.1 Complex arithmetic <complex.h>
         7.31.2 Character handling <ctype.h>
         7.31.3 Errors <errno.h>
         7.31.4 Floating-point environment <fenv.h>
         7.31.5 Format conversion of integer types <inttypes.h>
         7.31.6 Localization <locale.h>
         7.31.7 Signal handling <signal.h>
         7.31.8 Atomics <stdatomic.h>
         7.31.9 Boolean type and values <stdbool.h>
         7.31.10 Integer types <stdint.h>
         7.31.11 Input/output <stdio.h>
         7.31.12 General utilities <stdlib.h>
            7.31.13 String handling <string.h>
            7.31.14 Date and time <time.h>
            7.31.15 Threads <threads.h>
            7.31.16 Extended multibyte and wide character utilities
                    <wchar.h>
            7.31.17 Wide character classification and mapping utilities
                    <wctype.h>
    Annex A (informative) Language syntax summary
      A.1 Lexical grammar
      A.2 Phrase structure grammar
      A.3 Preprocessing directives
    Annex B (informative) Library summary
      B.1 Diagnostics <assert.h>
      B.2 Complex <complex.h>
      B.3 Character handling <ctype.h>
      B.4 Errors <errno.h>
      B.5 Floating-point environment <fenv.h>
      B.6 Characteristics of floating types <float.h>
      B.7 Format conversion of integer types <inttypes.h>
      B.8 Alternative spellings <iso646.h>
      B.9 Sizes of integer types <limits.h>
      B.10 Localization <locale.h>
      B.11 Mathematics <math.h>
      B.12 Nonlocal jumps <setjmp.h>
      B.13 Signal handling <signal.h>
      B.14 Alignment <stdalign.h>
      B.15 Variable arguments <stdarg.h>
      B.16 Atomics <stdatomic.h>
      B.17 Boolean type and values <stdbool.h>
      B.18 Common definitions <stddef.h>
      B.19 Integer types <stdint.h>
      B.20 Input/output <stdio.h>
      B.21 General utilities <stdlib.h>
      B.22 _Noreturn <stdnoreturn.h>
      B.23 String handling <string.h>
      B.24 Type-generic math <tgmath.h>
      B.25 Threads <threads.h>
      B.26 Date and time <time.h>
      B.27 Unicode utilities <uchar.h>
      B.28 Extended multibyte/wide character utilities <wchar.h>
      B.29 Wide character classification and mapping utilities <wctype.h>
    Annex C (informative) Sequence points
    Annex D (normative) Universal character names for identifiers
      D.1 Ranges of characters allowed
      D.2 Ranges of characters disallowed initially
    Annex E (informative) Implementation limits
    Annex F (normative) IEC 60559 floating-point arithmetic
      F.1 Introduction
      F.2 Types
      F.3 Operators and functions
      F.4 Floating to integer conversion
      F.5 Binary-decimal conversion
      F.6 The return statement
      F.7 Contracted expressions
      F.8 Floating-point environment
      F.9 Optimization
      F.10 Mathematics <math.h>
            F.10.1 Trigonometric functions
            F.10.2 Hyperbolic functions
            F.10.3 Exponential and logarithmic functions
            F.10.4 Power and absolute value functions
            F.10.5 Error and gamma functions
            F.10.6 Nearest integer functions
            F.10.7 Remainder functions
            F.10.8 Manipulation functions
            F.10.9 Maximum, minimum, and positive difference functions
            F.10.10 Floating multiply-add
            F.10.11 Comparison macros
    Annex G (normative) IEC 60559-compatible complex arithmetic
      G.1 Introduction
      G.2 Types
      G.3 Conventions
      G.4 Conversions
           G.4.1 Imaginary types
           G.4.2 Real and imaginary
           G.4.3 Imaginary and complex
      G.5 Binary operators
           G.5.1 Multiplicative operators
           G.5.2 Additive operators
      G.6 Complex arithmetic <complex.h>
           G.6.1 Trigonometric functions
           G.6.2 Hyperbolic functions
           G.6.3 Exponential and logarithmic functions
           G.6.4 Power and absolute-value functions
      G.7 Type-generic math <tgmath.h>
    Annex H (informative) Language independent arithmetic
      H.1 Introduction
      H.2 Types
      H.3 Notification
    Annex I (informative) Common warnings
    Annex J (informative) Portability issues
      J.1 Unspecified behavior
      J.2 Undefined behavior
      J.3 Implementation-defined behavior
      J.4 Locale-specific behavior
      J.5 Common extensions
    Annex K (normative) Bounds-checking interfaces
      K.1 Background
      K.2 Scope
      K.3 Library
           K.3.1 Introduction
                    K.3.1.1 Standard headers
                    K.3.1.2 Reserved identifiers
                    K.3.1.3 Use of errno
                    K.3.1.4 Runtime-constraint violations
           K.3.2 Errors <errno.h>
           K.3.3 Common definitions <stddef.h>
           K.3.4 Integer types <stdint.h>
           K.3.5 Input/output <stdio.h>
                    K.3.5.1 Operations on files     .
                    K.3.5.2 File access functions
                    K.3.5.3 Formatted input/output functions
                    K.3.5.4 Character input/output functions
           K.3.6 General utilities <stdlib.h>
                    K.3.6.1 Runtime-constraint handling
                    K.3.6.2 Communication with the environment
                    K.3.6.3 Searching and sorting utilities
                    K.3.6.4 Multibyte/wide character conversion functions
                    K.3.6.5 Multibyte/wide string conversion functions
           K.3.7 String handling <string.h>
                    K.3.7.1 Copying functions
                    K.3.7.2 Concatenation functions
                    K.3.7.3 Search functions
                    K.3.7.4 Miscellaneous functions
           K.3.8 Date and time <time.h>
                    K.3.8.1 Components of time
                    K.3.8.2 Time conversion functions
            K.3.9   Extended multibyte and wide character utilities
                    <wchar.h>
                    K.3.9.1 Formatted wide character input/output functions
                    K.3.9.2 General wide string utilities
                    K.3.9.3 Extended multibyte/wide character conversion
                            utilities
    Annex L (normative) Analyzability
      L.1 Scope
      L.2 Definitions
      L.3 Requirements

### FOREWORD. [Foreword]

    1   ISO (the International Organization for Standardization) and IEC (the International
        Electrotechnical Commission) form the specialized system for worldwide
        standardization. National bodies that are member of ISO or IEC participate in the
        development of International Standards through technical committees established by the
        respective organization to deal with particular fields of technical activity. ISO and IEC
        technical committees collaborate in fields of mutual interest. Other international
        organizations, governmental and non-governmental, in liaison with ISO and IEC, also
        take part in the work.

    2   International Standards are drafted in accordance with the rules given in the ISO/IEC
        Directives, Part 2. This International Standard was drafted in accordance with the fifth
        edition (2004).

    3   In the field of information technology, ISO and IEC have established a joint technical
        committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
        committee are circulated to national bodies for voting. Publication as an International
        Standard requires approval by at least 75% of the national bodies casting a vote.

    4   Attention is drawn to the possibility that some of the elements of this document may be
        the subject of patent rights. ISO and IEC shall not be held responsible for identifying any
        or all such patent rights.

    5   This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1,
        Information technology, Subcommittee SC 22, Programming languages, their
        environments and system software interfaces. The Working Group responsible for this
        standard (WG 14) maintains a site on the World Wide Web at http://www.open-
        std.org/JTC1/SC22/WG14/ containing additional information relevant to this
        standard such as a Rationale for many of the decisions made during its preparation and a
        log of Defect Reports and Responses.

    6   This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as
        corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and
        ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:
        — conditional (optional) features (including some that were previously mandatory)
        — support for multiple threads of execution including an improved memory sequencing
          model, atomic objects, and thread-local storage (<stdatomic.h> and
          <threads.h>)
        — additional floating-point characteristic macros (<float.h>)
        — querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
        — Unicode characters and           strings   (<uchar.h>)       (originally   specified   in
          ISO/IEC TR 19769:2004)
        — type-generic expressions
        — static assertions
        — anonymous structures and unions
        — no-return functions
        — macros to create complex numbers (<complex.h>)
        — support for opening files for exclusive access
        — removed the gets function (<stdio.h>)
        — added the aligned_alloc, at_quick_exit, and quick_exit functions
          (<stdlib.h>)
        — (conditional) support for bounds-checking interfaces (originally specified in
          ISO/IEC TR 24731−1:2007)
        — (conditional) support for analyzability

    7   Major changes in the second edition included:
        — restricted character set support via digraphs and <iso646.h> (originally specified
          in AMD1)
        — wide character library support in <wchar.h> and <wctype.h> (originally
          specified in AMD1)
        — more precise aliasing rules via effective type
        — restricted pointers
        — variable length arrays
        — flexible array members
        — static and type qualifiers in parameter array declarators
        — complex (and imaginary) support in <complex.h>
        — type-generic math macros in <tgmath.h>
        — the long long int type and library functions
        — increased minimum translation limits
        — additional floating-point characteristics in <float.h>
        — remove implicit int
        — reliable integer division
        — universal character names (\u and \U)
        — extended identifiers
        — hexadecimal floating-point constants and %a and %A printf/scanf conversion
          specifiers
    — compound literals
    — designated initializers
    — // comments
    — extended integer types and library functions in <inttypes.h> and <stdint.h>
    — remove implicit function declaration
    — preprocessor arithmetic done in intmax_t/uintmax_t
    — mixed declarations and code
    — new block scopes for selection and iteration statements
    — integer constant type rules
    — integer promotion rules
    — macros with a variable number of arguments
    — the vscanf family of functions in <stdio.h> and <wchar.h>
    — additional math library functions in <math.h>
    — treatment of error conditions by math library functions (math_errhandling)
    — floating-point environment access in <fenv.h>
    — IEC 60559 (also known as IEC 559 or IEEE arithmetic) support
    — trailing comma allowed in enum declaration
    — %lf conversion specifier allowed in printf
    — inline functions
    — the snprintf family of functions in <stdio.h>
    — boolean type in <stdbool.h>
    — idempotent type qualifiers
    — empty macro arguments
    — new structure type compatibility rules (tag compatibility)
    — additional predefined macro names
    — _Pragma preprocessing operator
    — standard pragmas
    — _ _func_ _ predefined identifier
    — va_copy macro
    — additional strftime conversion specifiers
    — LIA compatibility annex
        — deprecate ungetc at the beginning of a binary file
        — remove deprecation of aliased array parameters
        — conversion of array to pointer not limited to lvalues
        — relaxed constraints on aggregate and union initialization
        — relaxed restrictions on portable header names
        — return without expression not permitted in function that returns a value (and vice
          versa)

    8   Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H,
        I, J, the bibliography, and the index are for information only. In accordance with Part 2 of
        the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples
        are also for information only.

### INTRO. [Introduction]

    1   With the introduction of new devices and extended character sets, new features may be
        added to this International Standard. Subclauses in the language and library clauses warn
        implementors and programmers of usages which, though valid in themselves, may
        conflict with future additions.

    2   Certain features are obsolescent, which means that they may be considered for
        withdrawal in future revisions of this International Standard. They are retained because
        of their widespread use, but their use in new implementations (for implementation
        features) or new programs (for language [6.11] or library features [7.31]) is discouraged.

    3   This International Standard is divided into four major subdivisions:
        — preliminary elements (clauses 1−4);
        — the characteristics of environments that translate and execute C programs (clause 5);
        — the language syntax, constraints, and semantics (clause 6);
        — the library facilities (clause 7).

    4   Examples are provided to illustrate possible forms of the constructions described.
        Footnotes are provided to emphasize consequences of the rules described in that
        subclause or elsewhere in this International Standard. References are used to refer to
        other related subclauses. Recommendations are provided to give advice or guidance to
        implementors. Annexes provide additional information and summarize the information
        contained in this International Standard. A bibliography lists documents that were
        referred to during the preparation of the standard.

    5   The language clause (clause 6) is derived from ‘‘The C Reference Manual’’.

    6   The library clause (clause 7) is based on the 1984 /usr/group Standard.

### 1. [Scope]

    1   This International Standard specifies the form and establishes the interpretation of
        programs written in the C programming language.[1] It specifies
        — the representation of C programs;
        — the syntax and constraints of the C language;
        — the semantic rules for interpreting C programs;
        — the representation of input data to be processed by C programs;
        — the representation of output data produced by C programs;
        — the restrictions and limits imposed by a conforming implementation of C.

    Footnote 1) This International Standard is designed to promote the portability of C programs among a variety of
             data-processing systems. It is intended for use by implementors and programmers.

    2   This International Standard does not specify
        — the mechanism by which C programs are transformed for use by a data-processing
          system;
        — the mechanism by which C programs are invoked for use by a data-processing
          system;
        — the mechanism by which input data are transformed for use by a C program;
        — the mechanism by which output data are transformed after being produced by a C
          program;
        — the size or complexity of a program and its data that will exceed the capacity of any
          specific data-processing system or the capacity of a particular processor;
        — all minimal requirements of a data-processing system that is capable of supporting a
          conforming implementation.

### 2. [Normative references]

    1   The following referenced documents are indispensable for the application of this
        document. For dated references, only the edition cited applies. For undated references,
        the latest edition of the referenced document (including any amendments) applies.

    2   ISO 31−11:1992, Quantities and units — Part 11: Mathematical signs and symbols for
        use in the physical sciences and technology.

    3   ISO/IEC 646, Information technology — ISO 7-bit coded character set for information
        interchange.

    4   ISO/IEC 2382−1:1993, Information technology — Vocabulary — Part 1: Fundamental
        terms.

    5   ISO 4217, Codes for the representation of currencies and funds.

    6   ISO 8601, Data elements and interchange formats — Information interchange —
        Representation of dates and times.

    7   ISO/IEC 10646 (all parts), Information technology — Universal Multiple-Octet Coded
        Character Set (UCS).

    8   IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
        designated IEC 559:1989).

### 3. [Terms, definitions, and symbols]

    1   For the purposes of this International Standard, the following definitions apply. Other
        terms are defined where they appear in italic type or on the left side of a syntax rule.
        Terms explicitly defined in this International Standard are not to be presumed to refer
        implicitly to similar terms defined elsewhere. Terms not defined in this International
        Standard are to be interpreted according to ISO/IEC 2382−1. Mathematical symbols not
        defined in this International Standard are to be interpreted according to ISO 31−11.

### 3.1 [Terms, definitions, and symbols]

    1   access
        ⟨execution-time action⟩ to read or modify the value of an object

    2   NOTE 1   Where only one of these two actions is meant, ‘‘read’’ or ‘‘modify’’ is used.

    3   NOTE 2   ‘‘Modify’’ includes the case where the new value being stored is the same as the previous value.

    4   NOTE 3   Expressions that are not evaluated do not access objects.

### 3.2 [Terms, definitions, and symbols]

    1   alignment
        requirement that objects of a particular type be located on storage boundaries with
        addresses that are particular multiples of a byte address

### 3.3 [Terms, definitions, and symbols]

    1   argument
        actual argument
        actual parameter (deprecated)
        expression in the comma-separated list bounded by the parentheses in a function call
        expression, or a sequence of preprocessing tokens in the comma-separated list bounded
        by the parentheses in a function-like macro invocation

### 3.4 [Terms, definitions, and symbols]

    1   behavior
        external appearance or action

### 3.4.1 [Terms, definitions, and symbols]

    1   implementation-defined behavior
        unspecified behavior where each implementation documents how the choice is made

    2   EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
        when a signed integer is shifted right.

### 3.4.2 [Terms, definitions, and symbols]

    1   locale-specific behavior
        behavior that depends on local conventions of nationality, culture, and language that each
        implementation documents

    2   EXAMPLE An example of locale-specific behavior is whether the islower function returns true for
        characters other than the 26 lowercase Latin letters.

### 3.4.3 [Terms, definitions, and symbols]

    1   undefined behavior
        behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
        for which this International Standard imposes no requirements

    2   NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
        results, to behaving during translation or program execution in a documented manner characteristic of the
        environment (with or without the issuance of a diagnostic message), to terminating a translation or
        execution (with the issuance of a diagnostic message).

    3   EXAMPLE        An example of undefined behavior is the behavior on integer overflow.

### 3.4.4 [Terms, definitions, and symbols]

    1   unspecified behavior
        use of an unspecified value, or other behavior where this International Standard provides
        two or more possibilities and imposes no further requirements on which is chosen in any
        instance

    2   EXAMPLE        An example of unspecified behavior is the order in which the arguments to a function are
        evaluated.

### 3.5 [Terms, definitions, and symbols]

    1   bit
        unit of data storage in the execution environment large enough to hold an object that may
        have one of two values

    2   NOTE      It need not be possible to express the address of each individual bit of an object.

### 3.6 [Terms, definitions, and symbols]

    1   byte
        addressable unit of data storage large enough to hold any member of the basic character
        set of the execution environment

    2   NOTE 1     It is possible to express the address of each individual byte of an object uniquely.

    3   NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-
        defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order
        bit.

### 3.7 [Terms, definitions, and symbols]

    1   character
        ⟨abstract⟩ member of a set of elements used for the organization, control, or
        representation of data

### 3.7.1 [Terms, definitions, and symbols]

    1   character
        single-byte character
        ⟨C⟩ bit representation that fits in a byte

### 3.7.2 [Terms, definitions, and symbols]

    1   multibyte character
        sequence of one or more bytes representing a member of the extended character set of
        either the source or the execution environment

    2   NOTE    The extended character set is a superset of the basic character set.

### 3.7.3 [Terms, definitions, and symbols]

    1   wide character
        value representable by an object of type wchar_t, capable of representing any character
        in the current locale

### 3.8 [Terms, definitions, and symbols]

    1   constraint
        restriction, either syntactic or semantic, by which the exposition of language elements is
        to be interpreted

### 3.9 [Terms, definitions, and symbols]

    1   correctly rounded result
        representation in the result format that is nearest in value, subject to the current rounding
        mode, to what the result would be given unlimited range and precision

### 3.10 [Terms, definitions, and symbols]

    1   diagnostic message
        message belonging to an implementation-defined subset of the implementation’s message
        output

### 3.11 [Terms, definitions, and symbols]

    1   forward reference
        reference to a later subclause of this International Standard that contains additional
        information relevant to this subclause

### 3.12 [Terms, definitions, and symbols]

    1   implementation
        particular set of software, running in a particular translation environment under particular
        control options, that performs translation of programs for, and supports execution of
        functions in, a particular execution environment

### 3.13 [Terms, definitions, and symbols]

    1   implementation limit
        restriction imposed upon programs by the implementation

### 3.14 [Terms, definitions, and symbols]

    1   memory location
        either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
        nonzero width

    2   NOTE 1 Two threads of execution can update and access separate memory locations without interfering
        with each other.

    3   NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same
        applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the
        two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member
        declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all
        members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those
        intervening bit-fields happen to be.

    4   EXAMPLE        A structure declared as
                 struct {
                       char a;
                       int b:5, c:11, :0, d:8;
                       struct { int ee:8; } e;
                 }
        contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
        memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
        and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
        modified, but b and a, for example, can be.

### 3.15 [Terms, definitions, and symbols]

    1   object
        region of data storage in the execution environment, the contents of which can represent
        values

    2   NOTE      When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.

### 3.16 [Terms, definitions, and symbols]

    1   parameter
        formal parameter
        formal argument (deprecated)
        object declared as part of a function declaration or definition that acquires a value on
        entry to the function, or an identifier from the comma-separated list bounded by the
        parentheses immediately following the macro name in a function-like macro definition

### 3.17 [Terms, definitions, and symbols]

    1   recommended practice
        specification that is strongly recommended as being in keeping with the intent of the
        standard, but that may be impractical for some implementations

### 3.18 [Terms, definitions, and symbols]

    1   runtime-constraint
        requirement on a program when calling a library function

    2   NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and
        need not be diagnosed at translation time.

    3   NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime-
        constraints for a library function are not violated by the program; see K.3.1.4.

### 3.19 [Terms, definitions, and symbols]

    1   value
        precise meaning of the contents of an object when interpreted as having a specific type

### 3.19.1 [Terms, definitions, and symbols]

    1   implementation-defined value
        unspecified value where each implementation documents how the choice is made

### 3.19.2 [Terms, definitions, and symbols]

    1   indeterminate value
        either an unspecified value or a trap representation

### 3.19.3 [Terms, definitions, and symbols]

    1   unspecified value
        valid value of the relevant type where this International Standard imposes no
        requirements on which value is chosen in any instance

    2   NOTE     An unspecified value cannot be a trap representation.

### 3.19.4 [Terms, definitions, and symbols]

    1   trap representation
        an object representation that need not represent a value of the object type

### 3.19.5 [Terms, definitions, and symbols]

    1   perform a trap
        interrupt execution of the program such that no further operations are performed

    2   NOTE In this International Standard, when the word ‘‘trap’’ is not immediately followed by
        ‘‘representation’’, this is the intended usage.[2]

    Footnote 2) For example, ‘‘Trapping or stopping (if supported) is disabled...’’ (F.8.2). Note that fetching a trap
             representation might perform a trap but is not required to (see 6.2.6.1).

### 3.20 [Terms, definitions, and symbols]

    1   ⎡ x⎤
        ceiling of x: the least integer greater than or equal to x

    2   EXAMPLE       ⎡2. 4⎤ is 3, ⎡−2. 4⎤ is −2.

### 3.21 [Terms, definitions, and symbols]

    1   ⎣ x⎦
        floor of x: the greatest integer less than or equal to x

    2   EXAMPLE       ⎣2. 4⎦ is 2, ⎣−2. 4⎦ is −3.

### 4. [Conformance]

    1   In this International Standard, ‘‘shall’’ is to be interpreted as a requirement on an
        implementation or on a program; conversely, ‘‘shall not’’ is to be interpreted as a
        prohibition.

    2   If a ‘‘shall’’ or ‘‘shall not’’ requirement that appears outside of a constraint or runtime-
        constraint is violated, the behavior is undefined. Undefined behavior is otherwise
        indicated in this International Standard by the words ‘‘undefined behavior’’ or by the
        omission of any explicit definition of behavior. There is no difference in emphasis among
        these three; they all describe ‘‘behavior that is undefined’’.

    3   A program that is correct in all other aspects, operating on correct data, containing
        unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.

    4   The implementation shall not successfully translate a preprocessing translation unit
        containing a #error preprocessing directive unless it is part of a group skipped by
        conditional inclusion.

    5   A strictly conforming program shall use only those features of the language and library
        specified in this International Standard.[3] It shall not produce output dependent on any
        unspecified, undefined, or implementation-defined behavior, and shall not exceed any
        minimum implementation limit.

    Footnote 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
             by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
                     #ifdef _ _STDC_IEC_559_ _ /* FE_UPWARD defined */
                        /* ... */
                        fesetround(FE_UPWARD);
                        /* ... */
                     #endif

    6   The two forms of conforming implementation are hosted and freestanding. A conforming
        hosted implementation shall accept any strictly conforming program. A conforming
        freestanding implementation shall accept any strictly conforming program in which the ∗
        use of the features specified in the library clause (clause 7) is confined to the contents of
        the standard headers <float.h>, <iso646.h>, <limits.h>, <stdalign.h>,
        <stdarg.h>,           <stdbool.h>,            <stddef.h>,           <stdint.h>,          and
        <stdnoreturn.h>. A conforming implementation may have extensions (including
        additional library functions), provided they do not alter the behavior of any strictly
        conforming program.[4]

    Footnote 4) This implies that a conforming implementation reserves no identifiers other than those explicitly
             reserved in this International Standard.

    7   A conforming program is one that is acceptable to a conforming implementation.[5]

    Footnote 5) Strictly conforming programs are intended to be maximally portable among conforming
             implementations. Conforming programs may depend upon nonportable features of a conforming
             implementation.

    8   An implementation shall be accompanied by a document that defines all implementation-
        defined and locale-specific characteristics and all extensions.
        Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
        characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>
        (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15),
        variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h>
        (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20),
        <stdnoreturn.h> (7.23).

### 5. [Environment]

    1   An implementation translates C source files and executes C programs in two data-
        processing-system environments, which will be called the translation environment and
        the execution environment in this International Standard. Their characteristics define and
        constrain the results of executing conforming C programs constructed according to the
        syntactic and semantic rules for conforming implementations.
        Forward references: In this clause, only a few of many possible forward references
        have been noted.

### 5.1 [Conceptual models]

### 5.1.1 [Translation environment]

### 5.1.1.1 [Program structure]

    1   A C program need not all be translated at the same time. The text of the program is kept
        in units called source files, (or preprocessing files) in this International Standard. A
        source file together with all the headers and source files included via the preprocessing
        directive #include is known as a preprocessing translation unit. After preprocessing, a
        preprocessing translation unit is called a translation unit. Previously translated translation
        units may be preserved individually or in libraries. The separate translation units of a
        program communicate by (for example) calls to functions whose identifiers have external
        linkage, manipulation of objects whose identifiers have external linkage, or manipulation
        of data files. Translation units may be separately translated and then later linked to
        produce an executable program.
        Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
        preprocessing directives (6.10).

### 5.1.1.2 [Translation phases]

    1   The precedence among the syntax rules of translation is specified by the following
        phases.[6]
             1.   Physical source file multibyte characters are mapped, in an implementation-
                  defined manner, to the source character set (introducing new-line characters for
                  end-of-line indicators) if necessary. Trigraph sequences are replaced by
                  corresponding single-character internal representations.
         2.   Each instance of a backslash character (\) immediately followed by a new-line
              character is deleted, splicing physical source lines to form logical source lines.
              Only the last backslash on any physical source line shall be eligible for being part
              of such a splice. A source file that is not empty shall end in a new-line character,
              which shall not be immediately preceded by a backslash character before any such
              splicing takes place.
         3.   The source file is decomposed into preprocessing tokens[7] and sequences of
              white-space characters (including comments). A source file shall not end in a
              partial preprocessing token or in a partial comment. Each comment is replaced by
              one space character. New-line characters are retained. Whether each nonempty
              sequence of white-space characters other than new-line is retained or replaced by
              one space character is implementation-defined.
         4. Preprocessing directives are executed, macro invocations are expanded, and
            _Pragma unary operator expressions are executed. If a character sequence that
            matches the syntax of a universal character name is produced by token
            concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
            directive causes the named header or source file to be processed from phase 1
            through phase 4, recursively. All preprocessing directives are then deleted.
         5. Each source character set member and escape sequence in character constants and
            string literals is converted to the corresponding member of the execution character
            set; if there is no corresponding member, it is converted to an implementation-
            defined member other than the null (wide) character.[8]
         6.   Adjacent string literal tokens are concatenated.
         7. White-space characters separating tokens are no longer significant. Each
            preprocessing token is converted into a token. The resulting tokens are
            syntactically and semantically analyzed and translated as a translation unit.
         8.   All external object and function references are resolved. Library components are
              linked to satisfy external references to functions and objects not defined in the
              current translation. All such translator output is collected into a program image
              which contains information needed for execution in its execution environment.
    Forward references: universal character names (6.4.3), lexical elements (6.4),
    preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).

    Footnote 6) Implementations shall behave as if these separate phases occur, even though many are typically folded
              together in practice. Source files, translation units, and translated translation units need not
              necessarily be stored as files, nor need there be any one-to-one correspondence between these entities
              and any external representation. The description is conceptual only, and does not specify any
              particular implementation.

    Footnote 7) As described in 6.4, the process of dividing a source file’s characters into preprocessing tokens is
              context-dependent. For example, see the handling of < within a #include preprocessing directive.

    Footnote 8) An implementation need not convert all non-corresponding source characters to the same execution
              character.

### 5.1.1.3 [Diagnostics]

    1   A conforming implementation shall produce at least one diagnostic message (identified in
        an implementation-defined manner) if a preprocessing translation unit or translation unit
        contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
        specified as undefined or implementation-defined. Diagnostic messages need not be
        produced in other circumstances.[9]

    Footnote 9) The intent is that an implementation should identify the nature of, and where possible localize, each
             violation. Of course, an implementation is free to produce any number of diagnostics as long as a
             valid program is still correctly translated. It may also successfully translate an invalid program.

    2   EXAMPLE        An implementation shall issue a diagnostic for the translation unit:
                 char i;
                 int i;
        because in those cases where wording in this International Standard describes the behavior for a construct
        as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.

### 5.1.2 [Execution environments]

    1   Two execution environments are defined: freestanding and hosted. In both cases,
        program startup occurs when a designated C function is called by the execution
        environment. All objects with static storage duration shall be initialized (set to their
        initial values) before program startup. The manner and timing of such initialization are
        otherwise unspecified. Program termination returns control to the execution
        environment.
        Forward references: storage durations of objects (6.2.4), initialization (6.7.9).

### 5.1.2.1 [Freestanding environment]

    1   In a freestanding environment (in which C program execution may take place without any
        benefit of an operating system), the name and type of the function called at program
        startup are implementation-defined. Any library facilities available to a freestanding
        program, other than the minimal set required by clause 4, are implementation-defined.

    2   The effect of program termination in a freestanding environment is implementation-
        defined.

### 5.1.2.2 [Hosted environment]

    1   A hosted environment need not be provided, but shall conform to the following
        specifications if present.

### 5.1.2.2.1 [Program startup]

    1   The function called at program startup is named main. The implementation declares no
        prototype for this function. It shall be defined with a return type of int and with no
        parameters:
                int main(void) { /* ... */ }
        or with two parameters (referred to here as argc and argv, though any names may be
        used, as they are local to the function in which they are declared):
                int main(int argc, char *argv[]) { /* ... */ }
        or equivalent;[10] or in some other implementation-defined manner.

    Footnote 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
            char ** argv, and so on.

    2   If they are declared, the parameters to the main function shall obey the following
        constraints:
        — The value of argc shall be nonnegative.
        — argv[argc] shall be a null pointer.
        — If the value of argc is greater than zero, the array members argv[0] through
          argv[argc-1] inclusive shall contain pointers to strings, which are given
          implementation-defined values by the host environment prior to program startup. The
          intent is to supply to the program information determined prior to program startup
          from elsewhere in the hosted environment. If the host environment is not capable of
          supplying strings with letters in both uppercase and lowercase, the implementation
          shall ensure that the strings are received in lowercase.
        — If the value of argc is greater than zero, the string pointed to by argv[0]
          represents the program name; argv[0][0] shall be the null character if the
          program name is not available from the host environment. If the value of argc is
          greater than one, the strings pointed to by argv[1] through argv[argc-1]
          represent the program parameters.
        — The parameters argc and argv and the strings pointed to by the argv array shall
          be modifiable by the program, and retain their last-stored values between program
          startup and program termination.

### 5.1.2.2.2 [Program execution]

    1   In a hosted environment, a program may use all the functions, macros, type definitions,
        and objects described in the library clause (clause 7).

### 5.1.2.2.3 [Program termination]

    1   If the return type of the main function is a type compatible with int, a return from the
        initial call to the main function is equivalent to calling the exit function with the value
        returned by the main function as its argument;[11] reaching the } that terminates the
        main function returns a value of 0. If the return type is not compatible with int, the
        termination status returned to the host environment is unspecified.
        Forward references: definition of terms (7.1.1), the exit function (7.22.4.4).

    Footnote 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
            will have ended in the former case, even where they would not have in the latter.

### 5.1.2.3 [Program execution]

    1   The semantic descriptions in this International Standard describe the behavior of an
        abstract machine in which issues of optimization are irrelevant.

    2   Accessing a volatile object, modifying an object, modifying a file, or calling a function
        that does any of those operations are all side effects,[12] which are changes in the state of
        the execution environment. Evaluation of an expression in general includes both value
        computations and initiation of side effects. Value computation for an lvalue expression
        includes determining the identity of the designated object.

    Footnote 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
            flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
            values of floating-point operations. Implementations that support such floating-point state are
            required to regard changes to it as side effects — see annex F for details. The floating-point
            environment library <fenv.h> provides a programming facility for indicating when these side
            effects matter, freeing the implementations in other cases.

    3   Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations
        executed by a single thread, which induces a partial order among those evaluations.
        Given any two evaluations A and B, if A is sequenced before B, then the execution of A
        shall precede the execution of B. (Conversely, if A is sequenced before B, then B is
        sequenced after A.) If A is not sequenced before or after B, then A and B are
        unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced
        either before or after B, but it is unspecified which.[13] The presence of a sequence point
        between the evaluation of expressions A and B implies that every value computation and
        side effect associated with A is sequenced before every value computation and side effect
        associated with B. (A summary of the sequence points is given in annex C.)

    Footnote 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations
            cannot interleave, but can be executed in any order.

    4   In the abstract machine, all expressions are evaluated as specified by the semantics. An
        actual implementation need not evaluate part of an expression if it can deduce that its
        value is not used and that no needed side effects are produced (including any caused by
         calling a function or accessing a volatile object).

    5    When the processing of the abstract machine is interrupted by receipt of a signal, the
         values of objects that are neither lock-free atomic objects nor of type volatile
         sig_atomic_t are unspecified, as is the state of the floating-point environment. The
         value of any object modified by the handler that is neither a lock-free atomic object nor of
         type volatile sig_atomic_t becomes indeterminate when the handler exits, as
         does the state of the floating-point environment if it is modified by the handler and not
         restored to its original state.

    6    The least requirements on a conforming implementation are:
         — Accesses to volatile objects are evaluated strictly according to the rules of the abstract
           machine.
         — At program termination, all data written into files shall be identical to the result that
           execution of the program according to the abstract semantics would have produced.
         — The input and output dynamics of interactive devices shall take place as specified in
           7.21.3. The intent of these requirements is that unbuffered or line-buffered output
           appear as soon as possible, to ensure that prompting messages actually appear prior to
           a program waiting for input.
         This is the observable behavior of the program.

    7    What constitutes an interactive device is implementation-defined.

    8    More stringent correspondences between abstract and actual semantics may be defined by
         each implementation.

    9    EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
         semantics: at every sequence point, the values of the actual objects would agree with those specified by the
         abstract semantics. The keyword volatile would then be redundant.

    10   Alternatively, an implementation might perform various optimizations within each translation unit, such
         that the actual semantics would agree with the abstract semantics only when making function calls across
         translation unit boundaries. In such an implementation, at the time of each function entry and function
         return where the calling function and the called function are in different translation units, the values of all
         externally linked objects and of all objects accessible via pointers therein would agree with the abstract
         semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
         function and of all objects accessible via pointers therein would agree with the abstract semantics. In this
         type of implementation, objects referred to by interrupt service routines activated by the signal function
         would require explicit specification of volatile storage, as well as other implementation-defined
         restrictions.

    11   EXAMPLE 2       In executing the fragment
                  char c1, c2;
                  /* ... */
                  c1 = c1 + c2;
         the ‘‘integer promotions’’ require that the abstract machine promote the value of each variable to int size
         and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
         overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
         produce the same result, possibly omitting the promotions.

    12   EXAMPLE 3       Similarly, in the fragment
                  float f1, f2;
                  double d;
                  /* ... */
                  f1 = f2 * d;
         the multiplication may be executed using single-precision arithmetic if the implementation can ascertain
         that the result would be the same as if it were executed using double-precision arithmetic (for example, if d
         were replaced by the constant 2.0, which has type double).

    13   EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
         semantics. Values are independent of whether they are represented in a register or in memory. For
         example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
         is required to round to the precision of the storage type. In particular, casts and assignments are required to
         perform their specified conversion. For the fragment
                  double d1, d2;
                  float f;
                  d1 = f = expression;
                  d2 = (float) expression;
         the values assigned to d1 and d2 are required to have been converted to float.

    14   EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in
         precision as well as range. The implementation cannot generally apply the mathematical associative rules
         for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of
         overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to
         rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
         numbers are often not valid (see F.9).
                  double x, y, z;
                  /* ... */
                  x = (x * y) * z; // not equivalent to x *= y * z;
                  z = (x - y) + y ; // not equivalent to z = x;
                  z = x + x * y;    // not equivalent to z = x * (1.0 + y);
                  y = x / 5.0;      // not equivalent to y = x * 0.2;

    15   EXAMPLE 6       To illustrate the grouping behavior of expressions, in the following fragment
                  int a, b;
                  /* ... */
                  a = a + 32760 + b + 5;
         the expression statement behaves exactly the same as
                  a = (((a + 32760) + b) + 5);
         due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
         next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in
         which overflows produce an explicit trap and in which the range of values representable by an int is
         [−32768, +32767], the implementation cannot rewrite this expression as
                  a = ((a + b) + 32765);
         since if the values for a and b were, respectively, −32754 and −15, the sum a + b would produce a trap
         while the original expression would not; nor can the expression be rewritten either as
                  a = ((a + 32765) + b);
         or
                  a = (a + (b + 32765));
         since the values for a and b might have been, respectively, 4 and −8 or −17 and 12. However, on a machine
         in which overflow silently generates some value and where positive and negative overflows cancel, the
         above expression statement can be rewritten by the implementation in any of the above ways because the
         same result will occur.

    16   EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the
         following fragment
                  #include <stdio.h>
                  int sum;
                  char *p;
                  /* ... */
                  sum = sum * 10 - '0' + (*p++ = getchar());
         the expression statement is grouped as if it were written as
                  sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
         but the actual increment of p can occur at any time between the previous sequence point and the next
         sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned
         value.

         Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), floating-
         point environment <fenv.h> (7.6), the signal function (7.14), files (7.21.3).

### 5.1.2.4 [Multi-threaded executions and data races]

    1    Under a hosted implementation, a program can have more than one thread of execution
         (or thread) running concurrently. The execution of each thread proceeds as defined by
         the remainder of this standard. The execution of the entire program consists of an
         execution of all of its threads.[14] Under a freestanding implementation, it is
         implementation-defined whether a program can have more than one thread of execution.

    Footnote 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of
             atomic operations, for example, allow executions inconsistent with a simple interleaving as described
             below.

    2    The value of an object visible to a thread T at a particular point is the initial value of the
         object, a value stored in the object by T , or a value stored in the object by another thread,
         according to the rules below.

    3    NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by
         the desire to support atomic operations with explicit and detailed visibility constraints. However, it also
         implicitly supports a simpler view for more restricted programs.

    4    Two expression evaluations conflict if one of them modifies a memory location and the
         other one reads or modifies the same memory location.

    5    The library defines a number of atomic operations (7.17) and operations on mutexes
         (7.26.4) that are specially identified as synchronization operations. These operations play
         a special role in making assignments in one thread visible to another. A synchronization
         operation on one or more memory locations is either an acquire operation, a release
         operation, both an acquire and release operation, or a consume operation. A
         synchronization operation without an associated memory location is a fence and can be
         either an acquire fence, a release fence, or both an acquire and release fence. In addition,
         there are relaxed atomic operations, which are not synchronization operations, and
         atomic read-modify-write operations, which have special characteristics.

    6    NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations
         composing the mutex. Correspondingly, a call that releases the same mutex will perform a release
         operation on those same locations. Informally, performing a release operation on A forces prior side effects
         on other memory locations to become visible to other threads that later perform an acquire or consume
         operation on A. We do not include relaxed atomic operations as synchronization operations although, like
         synchronization operations, they cannot contribute to data races.

    7    All modifications to a particular atomic object M occur in some particular total order,
         called the modification order of M. If A and B are modifications of an atomic object M,
         and A happens before B, then A shall precede B in the modification order of M, which is
         defined below.

    8    NOTE 3     This states that the modification orders must respect the ‘‘happens before’’ relation.

    9    NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be
         combined into a single total order for all objects. In general this will be impossible since different threads
         may observe modifications to different variables in inconsistent orders.

    10   A release sequence headed by a release operation A on an atomic object M is a maximal
         contiguous sub-sequence of side effects in the modification order of M, where the first
         operation is A and every subsequent operation either is performed by the same thread that
         performed the release or is an atomic read-modify-write operation.

    11   Certain library calls synchronize with other library calls performed by another thread. In
         particular, an atomic operation A that performs a release operation on an object M
         synchronizes with an atomic operation B that performs an acquire operation on M and
         reads a value written by any side effect in the release sequence headed by A.

    12   NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as
         described below. Such a requirement would sometimes interfere with efficient implementation.

    13   NOTE 6 The specifications of the synchronization operations define when one reads the value written by
         another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total
         order. Each mutex acquisition ‘‘reads the value written’’ by the last mutex release.

    14   An evaluation A carries a dependency [15] to an evaluation B if:
         — the value of A is used as an operand of B, unless:
               • B is an invocation of the kill_dependency macro,

               •   A is the left operand of a && or || operator,
               •   A is the left operand of a ? : operator, or
               •   A is the left operand of a , operator;
             or
         — A writes a scalar object or bit-field M, B reads from M the value written by A, and A
           is sequenced before B, or
         — for some evaluation X, A carries a dependency to X and X carries a dependency to B.

    Footnote 15) The ‘‘carries a dependency’’ relation is a subset of the ‘‘sequenced before’’ relation, and is similarly
             strictly intra-thread.

    15   An evaluation A is dependency-ordered before[16] an evaluation B if:
         — A performs a release operation on an atomic object M, and, in another thread, B
           performs a consume operation on M and reads a value written by any side effect in
           the release sequence headed by A, or
         — for some evaluation X, A is dependency-ordered before X and X carries a
           dependency to B.

    Footnote 16) The ‘‘dependency-ordered before’’ relation is analogous to the ‘‘synchronizes with’’ relation, but uses
             release/consume in place of release/acquire.

    16   An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A
         is dependency-ordered before B, or, for some evaluation X:
         — A synchronizes with X and X is sequenced before B,
         — A is sequenced before X and X inter-thread happens before B, or
         — A inter-thread happens before X and X inter-thread happens before B.

    17   NOTE 7 The ‘‘inter-thread happens before’’ relation describes arbitrary concatenations of ‘‘sequenced
         before’’, ‘‘synchronizes with’’, and ‘‘dependency-ordered before’’ relationships, with two exceptions. The
         first exception is that a concatenation is not permitted to end with ‘‘dependency-ordered before’’ followed
         by ‘‘sequenced before’’. The reason for this limitation is that a consume operation participating in a
         ‘‘dependency-ordered before’’ relationship provides ordering only with respect to operations to which this
         consume operation actually carries a dependency. The reason that this limitation applies only to the end of
         such a concatenation is that any subsequent release operation will provide the required ordering for a prior
         consume operation. The second exception is that a concatenation is not permitted to consist entirely of
         ‘‘sequenced before’’. The reasons for this limitation are (1) to permit ‘‘inter-thread happens before’’ to be
         transitively closed and (2) the ‘‘happens before’’ relation, defined below, provides for relationships
         consisting entirely of ‘‘sequenced before’’.

    18   An evaluation A happens before an evaluation B if A is sequenced before B or A inter-
         thread happens before B.

    19   A visible side effect A on an object M with respect to a value computation B of M
         satisfies the conditions:
         — A happens before B, and
         — there is no other side effect X to M such that A happens before X and X happens
             before B.
         The value of a non-atomic scalar object M, as determined by evaluation B, shall be the
         value stored by the visible side effect A.

    20   NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data
         race and the behavior is undefined.

    21   NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually
         detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable
         restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent)
         execution.

    22   The visible sequence of side effects on an atomic object M, with respect to a value
         computation B of M, is a maximal contiguous sub-sequence of side effects in the
         modification order of M, where the first side effect is visible with respect to B, and for
         every subsequent side effect, it is not the case that B happens before it. The value of an
         atomic object M, as determined by evaluation B, shall be the value stored by some
         operation in the visible sequence of M with respect to B. Furthermore, if a value
         computation A of an atomic object M happens before a value computation B of M, and
         the value computed by A corresponds to the value stored by side effect X, then the value
         computed by B shall either equal the value computed by A, or be the value stored by side
         effect Y , where Y follows X in the modification order of M.

    23   NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if
         both operations are ‘‘relaxed’’ loads. By doing so, we effectively make the ‘‘cache coherence’’ guarantee
         provided by most hardware available to C atomic operations.

    24   NOTE 11 The visible sequence depends on the ‘‘happens before’’ relation, which in turn depends on the
         values observed by loads of atomics, which we are restricting here. The intended reading is that there must
         exist an association of atomic loads with modifications they observe that, together with suitably chosen
         modification orders and the ‘‘happens before’’ relation derived as described above, satisfy the resulting
         constraints as imposed here.

    25   The execution of a program contains a data race if it contains two conflicting actions in
         different threads, at least one of which is not atomic, and neither happens before the
         other. Any such data race results in undefined behavior.

    26   NOTE 12 It can be shown that programs that correctly use simple mutexes and
         memory_order_seq_cst operations to prevent all data races, and use no other synchronization
         operations, behave as though the operations executed by their constituent threads were simply interleaved,
         with each value computation of an object being the last value stored in that interleaving. This is normally
         referred to as ‘‘sequential consistency’’. However, this applies only to data-race-free programs, and data-
         race-free programs cannot observe most program transformations that do not change single-threaded
         program semantics. In fact, most single-threaded program transformations continue to be allowed, since
         any program that behaves differently as a result must contain undefined behavior.

    27   NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location
         that would not be modified by the abstract machine are generally precluded by this standard, since such an
         assignment might overwrite another assignment by a different thread in cases in which an abstract machine
         execution would not have encountered a data race. This includes implementations of data member
         assignment that overwrite adjacent members in separate memory locations. We also generally preclude
         reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the
         "visible sequence" rules.

    28   NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may
         not preserve the semantics of the program as defined in this standard, since they potentially introduce a data
         race. However, they are typically valid in the context of an optimizing compiler that targets a specific
         machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that
         is not tolerant of races or provides hardware race detection.

### 5.2 [Environmental considerations]

### 5.2.1 [Character sets]

    1   Two sets of characters and their associated collating sequences shall be defined: the set in
        which source files are written (the source character set), and the set interpreted in the
        execution environment (the execution character set). Each set is further divided into a
        basic character set, whose contents are given by this subclause, and a set of zero or more
        locale-specific members (which are not members of the basic character set) called
        extended characters. The combined set is also called the extended character set. The
        values of the members of the execution character set are implementation-defined.

    2   In a character constant or string literal, members of the execution character set shall be
        represented by corresponding members of the source character set or by escape
        sequences consisting of the backslash \ followed by one or more characters. A byte with
        all bits set to 0, called the null character, shall exist in the basic execution character set; it
        is used to terminate a character string.

    3   Both the basic source and basic execution character sets shall have the following
        members: the 26 uppercase letters of the Latin alphabet
                A    B   C      D   E   F    G    H    I    J    K    L   M
                N    O   P      Q   R   S    T    U    V    W    X    Y   Z
        the 26 lowercase letters of the Latin alphabet
                a    b   c      d   e   f    g    h    i    j    k    l   m
                n    o   p      q   r   s    t    u    v    w    x    y   z
        the 10 decimal digits
                0    1   2      3   4   5    6    7    8    9
        the following 29 graphic characters
                !    "   #      %   &   '    (    )    *    +    ,    -   .    /    :
                ;    <   =      >   ?   [    \    ]    ^    _    {    |   }    ~
        the space character, and control characters representing horizontal tab, vertical tab, and
        form feed. The representation of each member of the source and execution basic
        character sets shall fit in a byte. In both the source and execution basic character sets, the
        value of each character after 0 in the above list of decimal digits shall be one greater than
        the value of the previous. In source files, there shall be some way of indicating the end of
        each line of text; this International Standard treats such an end-of-line indicator as if it
        were a single new-line character. In the basic execution character set, there shall be
        control characters representing alert, backspace, carriage return, and new line. If any
        other characters are encountered in a source file (except in an identifier, a character
        constant, a string literal, a header name, a comment, or a preprocessing token that is never
        converted to a token), the behavior is undefined.

    4   A letter is an uppercase letter or a lowercase letter as defined above; in this International
        Standard the term does not include other characters that are letters in other alphabets.

    5   The universal character name construct provides a way to name other characters.
        Forward references: universal character names (6.4.3), character constants (6.4.4.4),
        preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).

### 5.2.1.1 [Trigraph sequences]

    1   Before any other processing takes place, each occurrence of one of the following
        sequences of three characters (called trigraph sequences[17]) is replaced with the
        corresponding single character.
               ??=      #                       ??)      ]                       ??!      |
               ??(      [                       ??'      ^                       ??>      }
               ??/      \                       ??<      {                       ??-      ~
        No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
        above is not changed.

    Footnote 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
            described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.

    2   EXAMPLE 1
                  ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
        becomes
                  #define arraycheck(a, b) a[b] || b[a]

    3   EXAMPLE 2       The following source line
                  printf("Eh???/n");
        becomes (after replacement of the trigraph sequence ??/)
                  printf("Eh?\n");

### 5.2.1.2 [Multibyte characters]

    1   The source character set may contain multibyte characters, used to represent members of
        the extended character set. The execution character set may also contain multibyte
        characters, which need not have the same encoding as for the source character set. For
        both character sets, the following shall hold:
        — The basic character set shall be present and each character shall be encoded as a
          single byte.
        — The presence, meaning, and representation of any additional members is locale-
          specific.
        — A multibyte character set may have a state-dependent encoding, wherein each
          sequence of multibyte characters begins in an initial shift state and enters other
          locale-specific shift states when specific multibyte characters are encountered in the
          sequence. While in the initial shift state, all single-byte characters retain their usual
          interpretation and do not alter the shift state. The interpretation for subsequent bytes
          in the sequence is a function of the current shift state.
        — A byte with all bits zero shall be interpreted as a null character independent of shift
          state. Such a byte shall not occur as part of any other multibyte character.

    2   For source files, the following shall hold:
        — An identifier, comment, string literal, character constant, or header name shall begin
          and end in the initial shift state.
        — An identifier, comment, string literal, character constant, or header name shall consist
          of a sequence of valid multibyte characters.

### 5.2.2 [Character display semantics]

    1   The active position is that location on a display device where the next character output by
        the fputc function would appear. The intent of writing a printing character (as defined
        by the isprint function) to a display device is to display a graphic representation of
        that character at the active position and then advance the active position to the next
        position on the current line. The direction of writing is locale-specific. If the active
        position is at the final position of a line (if there is one), the behavior of the display device
        is unspecified.

    2   Alphabetic escape sequences representing nongraphic characters in the execution
        character set are intended to produce actions on display devices as follows:
        \a (alert) Produces an audible or visible alert without changing the active position.
        \b (backspace) Moves the active position to the previous position on the current line. If
           the active position is at the initial position of a line, the behavior of the display
           device is unspecified.
        \f ( form feed) Moves the active position to the initial position at the start of the next
           logical page.
        \n (new line) Moves the active position to the initial position of the next line.
        \r (carriage return) Moves the active position to the initial position of the current line.
        \t (horizontal tab) Moves the active position to the next horizontal tabulation position
           on the current line. If the active position is at or past the last defined horizontal
           tabulation position, the behavior of the display device is unspecified.
        \v (vertical tab) Moves the active position to the initial position of the next vertical
           tabulation position. If the active position is at or past the last defined vertical
             tabulation position, the behavior of the display device is unspecified.

    3   Each of these escape sequences shall produce a unique implementation-defined value
        which can be stored in a single char object. The external representations in a text file
        need not be identical to the internal representations, and are outside the scope of this
        International Standard.
        Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3).

### 5.2.3 [Signals and interrupts]

    1   Functions shall be implemented such that they may be interrupted at any time by a signal,
        or may be called by a signal handler, or both, with no alteration to earlier, but still active,
        invocations’ control flow (after the interruption), function return values, or objects with
        automatic storage duration. All such objects shall be maintained outside the function
        image (the instructions that compose the executable representation of a function) on a
        per-invocation basis.

### 5.2.4 [Environmental limits]

    1   Both the translation and execution environments constrain the implementation of
        language translators and libraries. The following summarizes the language-related
        environmental limits on a conforming implementation; the library-related limits are
        discussed in clause 7.

### 5.2.4.1 [Translation limits]

    1   The implementation shall be able to translate and execute at least one program that
        contains at least one instance of every one of the following limits:[18]
        — 127 nesting levels of blocks
        — 63 nesting levels of conditional inclusion
        — 12 pointer, array, and function declarators (in any combinations) modifying an
          arithmetic, structure, union, or void type in a declaration
        — 63 nesting levels of parenthesized declarators within a full declarator
        — 63 nesting levels of parenthesized expressions within a full expression
        — 63 significant initial characters in an internal identifier or a macro name (each
          universal character name or extended source character is considered a single
          character)
        — 31 significant initial characters in an external identifier (each universal character name
          specifying a short identifier of 0000FFFF or less is considered 6 characters, each
            universal character name specifying a short identifier of 00010000 or more is
            considered 10 characters, and each extended source character is considered the same
            number of characters as the corresponding universal character name, if any)[19]
        — 4095 external identifiers in one translation unit
        — 511 identifiers with block scope declared in one block
        — 4095 macro identifiers simultaneously defined in one preprocessing translation unit
        — 127 parameters in one function definition
        — 127 arguments in one function call
        — 127 parameters in one macro definition
        — 127 arguments in one macro invocation
        — 4095 characters in a logical source line
        — 4095 characters in a string literal (after concatenation)
        — 65535 bytes in an object (in a hosted environment only)
        — 15 nesting levels for #included files
        — 1023 case labels for a switch statement (excluding those for any nested switch
          statements)
        — 1023 members in a single structure or union
        — 1023 enumeration constants in a single enumeration
        — 63 levels of nested structure or union definitions in a single struct-declaration-list

    Footnote 18) Implementations should avoid imposing fixed translation limits whenever possible.

    Footnote 19) See ‘‘future language directions’’ (6.11.3).

### 5.2.4.2 [Numerical limits]

    1   An implementation is required to document all the limits specified in this subclause,
        which are specified in the headers <limits.h> and <float.h>. Additional limits are
        specified in <stdint.h>.
        Forward references: integer types <stdint.h> (7.20).

### 5.2.4.2.1 [Sizes of integer types <limits.h>]

    1   The values given below shall be replaced by constant expressions suitable for use in #if
        preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the
        following shall be replaced by expressions that have the same type as would an
        expression that is an object of the corresponding type converted according to the integer
        promotions. Their implementation-defined values shall be equal or greater in magnitude
    (absolute value) to those shown, with the same sign.
    — number of bits for smallest object that is not a bit-field (byte)
      CHAR_BIT                                            8
    — minimum value for an object of type signed char
      SCHAR_MIN                                -127 // −(27 − 1)
    — maximum value for an object of type signed char
      SCHAR_MAX                                +127 // 27 − 1
    — maximum value for an object of type unsigned char
      UCHAR_MAX                                 255 // 28 − 1
    — minimum value for an object of type char
      CHAR_MIN                               see below
    — maximum value for an object of type char
      CHAR_MAX                              see below
    — maximum number of bytes in a multibyte character, for any supported locale
      MB_LEN_MAX                                    1
    — minimum value for an object of type short int
      SHRT_MIN                               -32767 // −(215 − 1)
    — maximum value for an object of type short int
      SHRT_MAX                               +32767 // 215 − 1
    — maximum value for an object of type unsigned short int
      USHRT_MAX                               65535 // 216 − 1
    — minimum value for an object of type int
      INT_MIN                                 -32767 // −(215 − 1)
    — maximum value for an object of type int
      INT_MAX                                +32767 // 215 − 1
    — maximum value for an object of type unsigned int
      UINT_MAX                                65535 // 216 − 1
    — minimum value for an object of type long int
      LONG_MIN                         -2147483647 // −(231 − 1)
    — maximum value for an object of type long int
      LONG_MAX                         +2147483647 // 231 − 1
    — maximum value for an object of type unsigned long int
      ULONG_MAX                         4294967295 // 232 − 1
        — minimum value for an object of type long long int
          LLONG_MIN          -9223372036854775807 // −(263 − 1)
        — maximum value for an object of type long long int
          LLONG_MAX          +9223372036854775807 // 263 − 1
        — maximum value for an object of type unsigned long long int
          ULLONG_MAX         18446744073709551615 // 264 − 1

    2   If the value of an object of type char is treated as a signed integer when used in an
        expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
        value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
        CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
        UCHAR_MAX.[20] The value UCHAR_MAX shall equal 2CHAR_BIT − 1.
        Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).

    Footnote 20) See 6.2.5.

### 5.2.4.2.2 [Characteristics of floating types <float.h>]

    1   The characteristics of floating types are defined in terms of a model that describes a
        representation of floating-point numbers and values that provide information about an
        implementation’s floating-point arithmetic.[21] The following parameters are used to
        define the model for each floating-point type:
               s         sign (±1)
               b         base or radix of exponent representation (an integer > 1)
               e         exponent (an integer between a minimum emin and a maximum emax )
               p         precision (the number of base-b digits in the significand)
                fk       nonnegative integers less than b (the significand digits)

    Footnote 21) The floating-point model is intended to clarify the description of each floating-point characteristic and
            does not require the floating-point arithmetic of the implementation to be identical.

    2   A floating-point number (x) is defined by the following model:
                          p
               x = sb e Σ f k b−k ,    emin ≤ e ≤ emax
                         k=1

    3   In addition to normalized floating-point numbers ( f 1 > 0 if x ≠ 0), floating types may be
        able to contain other kinds of floating-point numbers, such as subnormal floating-point
        numbers (x ≠ 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x ≠ 0,
        e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
        NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
        through almost every arithmetic operation without raising a floating-point exception; a
        signaling NaN generally raises a floating-point exception when occurring as an
        arithmetic operand.[22]

    Footnote 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
            IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with
            similar behavior.

    4   An implementation may give zero and values that are not floating-point numbers (such as
        infinities and NaNs) a sign or may leave them unsigned. Wherever such values are
        unsigned, any requirement in this International Standard to retrieve the sign shall produce
        an unspecified sign, and any requirement to set the sign shall be ignored.

    5   The minimum range of representable values for a floating type is the most negative finite
        floating-point number representable in that type through the most positive finite floating-
        point number representable in that type. In addition, if negative infinity is representable
        in a type, the range of that type is extended to all negative real numbers; likewise, if
        positive infinity is representable in a type, the range of that type is extended to all positive
        real numbers.

    6   The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
        <math.h> and <complex.h> that return floating-point results is implementation-
        defined, as is the accuracy of the conversion between floating-point internal
        representations and string representations performed by the library functions in
        <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the
        accuracy is unknown.

    7   All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant
        expressions suitable for use in #if preprocessing directives; all floating values shall be
        constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX,
        and FLT_ROUNDS have separate names for all three floating-point types. The floating-
        point model representation is provided for all values except FLT_EVAL_METHOD and
        FLT_ROUNDS.

    8   The rounding mode for floating-point addition is characterized by the implementation-
        defined value of FLT_ROUNDS:[23]
              -1      indeterminable
               0      toward zero
               1      to nearest
               2      toward positive infinity
               3      toward negative infinity
        All other values for FLT_ROUNDS characterize implementation-defined rounding
        behavior.

    Footnote 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through
            the function fesetround in <fenv.h>.

    9    Except for assignment and cast (which remove all extra range and precision), the values
         yielded by operators with floating operands and values subject to the usual arithmetic
         conversions and of floating constants are evaluated to a format whose range and precision
         may be greater than required by the type. The use of evaluation formats is characterized
         by the implementation-defined value of FLT_EVAL_METHOD:[24]
                -1         indeterminable;
                  0        evaluate all operations and constants just to the range and precision of the
                           type;
                  1        evaluate operations and constants of type float and double to the
                           range and precision of the double type, evaluate long double
                           operations and constants to the range and precision of the long double
                           type;
                  2        evaluate all operations and constants to the range and precision of the
                           long double type.
         All other negative values for FLT_EVAL_METHOD characterize implementation-defined
         behavior.

    Footnote 24) The evaluation method determines evaluation formats of expressions involving all floating types, not
             just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float
             _Complex operands is represented in the double _Complex format, and its parts are evaluated to
             double.

    10   The presence or absence of subnormal numbers is characterized by the implementation-
         defined    values     of    FLT_HAS_SUBNORM,          DBL_HAS_SUBNORM,           and
         LDBL_HAS_SUBNORM:
                -1       indeterminable[25]
                 0       absent[26] (type does not support subnormal numbers)
                 1       present (type does support subnormal numbers)

    Footnote 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret
             subnormal representations as zero, nor as nonzero.

    Footnote 26) Characterization as absent is intended if no floating-point operations produce subnormal results from
             non-subnormal inputs, even if the type format includes representations of subnormal numbers.

    11   The values given in the following list shall be replaced by constant expressions with
         implementation-defined values that are greater or equal in magnitude (absolute value) to
         those shown, with the same sign:
         — radix of exponent representation, b
           FLT_RADIX                                                     2
    — number of base-FLT_RADIX digits in the floating-point significand, p
       FLT_MANT_DIG
       DBL_MANT_DIG
       LDBL_MANT_DIG
    — number of decimal digits, n, such that any floating-point number with p radix b digits
      can be rounded to a floating-point number with n decimal digits and back again
      without change to the value,
           ⎧ p log10 b        if b is a power of 10
           ⎨
           ⎩ ⎡1 + p log10 b⎤ otherwise
       FLT_DECIMAL_DIG                                   6
       DBL_DECIMAL_DIG                                  10
       LDBL_DECIMAL_DIG                                 10
    — number of decimal digits, n, such that any floating-point number in the widest
      supported floating type with pmax radix b digits can be rounded to a floating-point
      number with n decimal digits and back again without change to the value,
           ⎧ pmax log10 b       if b is a power of 10
           ⎨
           ⎩ ⎡1 + pmax log10 b⎤ otherwise
       DECIMAL_DIG                                    10
    — number of decimal digits, q, such that any floating-point number with q decimal digits
      can be rounded into a floating-point number with p radix b digits and back again
      without change to the q decimal digits,
           ⎧ p log10 b          if b is a power of 10
           ⎨
           ⎩ ⎣( p − 1) log10 b⎦ otherwise
       FLT_DIG                                         6
       DBL_DIG                                        10
       LDBL_DIG                                       10
    — minimum negative integer such that FLT_RADIX raised to one less than that power is
      a normalized floating-point number, emin
       FLT_MIN_EXP
       DBL_MIN_EXP
       LDBL_MIN_EXP
         — minimum negative integer such that 10 raised to that power is in the range of
           normalized floating-point numbers, ⎡log10 b emin −1 ⎤
                                              ⎢                ⎥
           FLT_MIN_10_EXP                                  -37
           DBL_MIN_10_EXP                                  -37
           LDBL_MIN_10_EXP                                 -37
         — maximum integer such that FLT_RADIX raised to one less than that power is a
           representable finite floating-point number, emax
            FLT_MAX_EXP
            DBL_MAX_EXP
            LDBL_MAX_EXP
         — maximum integer such that 10 raised to that power is in the range of representable
           finite floating-point numbers, ⎣log10 ((1 − b− p )b emax )⎦
            FLT_MAX_10_EXP                                 +37
            DBL_MAX_10_EXP                                 +37
            LDBL_MAX_10_EXP                                +37

    12   The values given in the following list shall be replaced by constant expressions with
         implementation-defined values that are greater than or equal to those shown:
         — maximum representable finite floating-point number, (1 − b− p )b emax
            FLT_MAX                                     1E+37
            DBL_MAX                                     1E+37
            LDBL_MAX                                    1E+37

    13   The values given in the following list shall be replaced by constant expressions with
         implementation-defined (positive) values that are less than or equal to those shown:
         — the difference between 1 and the least value greater than 1 that is representable in the
           given floating point type, b1− p
            FLT_EPSILON                                   1E-5
            DBL_EPSILON                                   1E-9
            LDBL_EPSILON                                  1E-9
         — minimum normalized positive floating-point number, b emin −1
            FLT_MIN                                     1E-37
            DBL_MIN                                     1E-37
            LDBL_MIN                                    1E-37
         — minimum positive floating-point number[27]
             FLT_TRUE_MIN                                       1E-37
             DBL_TRUE_MIN                                       1E-37
             LDBL_TRUE_MIN                                      1E-37
         Recommended practice

    Footnote 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a
             positive number no greater than the minimum normalized positive number for the type.

    14   Conversion from (at least) double to decimal with DECIMAL_DIG digits and back
         should be the identity function.

    15   EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
         requirements of this International Standard, and the appropriate values in a <float.h> header for type
         float:
                          6
               x = s16e Σ f k 16−k , −31 ≤ e ≤ +32
                         k=1
                 FLT_RADIX                                   16
                 FLT_MANT_DIG                                 6
                 FLT_EPSILON                    9.53674316E-07F
                 FLT_DECIMAL_DIG                              9
                 FLT_DIG                                      6
                 FLT_MIN_EXP                                -31
                 FLT_MIN                        2.93873588E-39F
                 FLT_MIN_10_EXP                             -38
                 FLT_MAX_EXP                                +32
                 FLT_MAX                        3.40282347E+38F
                 FLT_MAX_10_EXP                             +38

    16   EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
         single-precision and double-precision numbers in IEC 60559,[28] and the appropriate values in a
         <float.h> header for types float and double:
                          24
               x f = s2e Σ f k 2−k , −125 ≤ e ≤ +128
                         k=1

                          53
               x d = s2e Σ f k 2−k , −1021 ≤ e ≤ +1024
                         k=1
                 FLT_RADIX                                    2
                 DECIMAL_DIG                                 17
                 FLT_MANT_DIG                                24
                 FLT_EPSILON                    1.19209290E-07F // decimal constant
                 FLT_EPSILON                           0X1P-23F // hex constant
                 FLT_DECIMAL_DIG                              9
            FLT_DIG                             6
            FLT_MIN_EXP                      -125
            FLT_MIN               1.17549435E-38F // decimal constant
            FLT_MIN                     0X1P-126F // hex constant
            FLT_TRUE_MIN          1.40129846E-45F // decimal constant
            FLT_TRUE_MIN                0X1P-149F // hex constant
            FLT_HAS_SUBNORM                     1
            FLT_MIN_10_EXP                    -37
            FLT_MAX_EXP                      +128
            FLT_MAX               3.40282347E+38F // decimal constant
            FLT_MAX               0X1.fffffeP127F // hex constant
            FLT_MAX_10_EXP                    +38
            DBL_MANT_DIG                       53
            DBL_EPSILON    2.2204460492503131E-16 // decimal constant
            DBL_EPSILON                   0X1P-52 // hex constant
            DBL_DECIMAL_DIG                    17
            DBL_DIG                            15
            DBL_MIN_EXP                     -1021
            DBL_MIN      2.2250738585072014E-308 // decimal constant
            DBL_MIN                     0X1P-1022 // hex constant
            DBL_TRUE_MIN 4.9406564584124654E-324 // decimal constant
            DBL_TRUE_MIN                0X1P-1074 // hex constant
            DBL_HAS_SUBNORM                     1
            DBL_MIN_10_EXP                   -307
            DBL_MAX_EXP                     +1024
            DBL_MAX      1.7976931348623157E+308 // decimal constant
            DBL_MAX        0X1.fffffffffffffP1023 // hex constant
            DBL_MAX_10_EXP                   +308
    If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
    example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of
    precision), then DECIMAL_DIG would be 21.

    Forward references:         conditional inclusion (6.10.1), complex arithmetic
    <complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>
    (7.29), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>
    (7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12).

    Footnote 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
             limits are one less than shown here.

### 6. [Language]

### 6.1 [Notation]

    1   In the syntax notation used in this clause, syntactic categories (nonterminals) are
        indicated by italic type, and literal words and character set members (terminals) by bold
        type. A colon (:) following a nonterminal introduces its definition. Alternative
        definitions are listed on separate lines, except when prefaced by the words ‘‘one of’’. An
        optional symbol is indicated by the subscript ‘‘opt’’, so that
                { expressionopt }
        indicates an optional expression enclosed in braces.

    2   When syntactic categories are referred to in the main text, they are not italicized and
        words are separated by spaces instead of hyphens.

    3   A summary of the language syntax is given in annex A.

### 6.2 [Concepts]

### 6.2.1 [Scopes of identifiers]

    1   An identifier can denote an object; a function; a tag or a member of a structure, union, or
        enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
        same identifier can denote different entities at different points in the program. A member
        of an enumeration is called an enumeration constant. Macro names and macro
        parameters are not considered further here, because prior to the semantic phase of
        program translation any occurrences of macro names in the source file are replaced by the
        preprocessing token sequences that constitute their macro definitions.

    2   For each different entity that an identifier designates, the identifier is visible (i.e., can be
        used) only within a region of program text called its scope. Different entities designated
        by the same identifier either have different scopes, or are in different name spaces. There
        are four kinds of scopes: function, file, block, and function prototype. (A function
        prototype is a declaration of a function that declares the types of its parameters.)

    3   A label name is the only kind of identifier that has function scope. It can be used (in a
        goto statement) anywhere in the function in which it appears, and is declared implicitly
        by its syntactic appearance (followed by a : and a statement).

    4   Every other identifier has scope determined by the placement of its declaration (in a
        declarator or type specifier). If the declarator or type specifier that declares the identifier
        appears outside of any block or list of parameters, the identifier has file scope, which
        terminates at the end of the translation unit. If the declarator or type specifier that
        declares the identifier appears inside a block or within the list of parameter declarations in
        a function definition, the identifier has block scope, which terminates at the end of the
        associated block. If the declarator or type specifier that declares the identifier appears
        within the list of parameter declarations in a function prototype (not part of a function
        definition), the identifier has function prototype scope, which terminates at the end of the
        function declarator. If an identifier designates two different entities in the same name
        space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end
        strictly before the scope of the other entity (the outer scope). Within the inner scope, the
        identifier designates the entity declared in the inner scope; the entity declared in the outer
        scope is hidden (and not visible) within the inner scope.

    5   Unless explicitly stated otherwise, where this International Standard uses the term
        ‘‘identifier’’ to refer to some entity (as opposed to the syntactic construct), it refers to the
        entity in the relevant name space whose declaration is visible at the point the identifier
        occurs.

    6   Two identifiers have the same scope if and only if their scopes terminate at the same
        point.

    7   Structure, union, and enumeration tags have scope that begins just after the appearance of
        the tag in a type specifier that declares the tag. Each enumeration constant has scope that
        begins just after the appearance of its defining enumerator in an enumerator list. Any
        other identifier has scope that begins just after the completion of its declarator.

    8   As a special case, a type name (which is not a declaration of an identifier) is considered to
        have a scope that begins just after the place within the type name where the omitted
        identifier would appear were it not omitted.
        Forward references: declarations (6.7), function calls (6.5.2.2), function definitions
        (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3),
        source file inclusion (6.10.2), statements (6.8).

### 6.2.2 [Linkages of identifiers]

    1   An identifier declared in different scopes or in the same scope more than once can be
        made to refer to the same object or function by a process called linkage.[29] There are
        three kinds of linkage: external, internal, and none.

    Footnote 29) There is no linkage between different identifiers.

    2   In the set of translation units and libraries that constitutes an entire program, each
        declaration of a particular identifier with external linkage denotes the same object or
        function. Within one translation unit, each declaration of an identifier with internal
        linkage denotes the same object or function. Each declaration of an identifier with no
        linkage denotes a unique entity.

    3   If the declaration of a file scope identifier for an object or a function contains the storage-
        class specifier static, the identifier has internal linkage.[30]

    Footnote 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see
            6.7.1.

    4   For an identifier declared with the storage-class specifier extern in a scope in which a
        prior declaration of that identifier is visible,[31] if the prior declaration specifies internal or
        external linkage, the linkage of the identifier at the later declaration is the same as the
        linkage specified at the prior declaration. If no prior declaration is visible, or if the prior
        declaration specifies no linkage, then the identifier has external linkage.

    Footnote 31) As specified in 6.2.1, the later declaration might hide the prior declaration.

    5   If the declaration of an identifier for a function has no storage-class specifier, its linkage
        is determined exactly as if it were declared with the storage-class specifier extern. If
        the declaration of an identifier for an object has file scope and no storage-class specifier,
        its linkage is external.

    6   The following identifiers have no linkage: an identifier declared to be anything other than
        an object or a function; an identifier declared to be a function parameter; a block scope
        identifier for an object declared without the storage-class specifier extern.

    7   If, within a translation unit, the same identifier appears with both internal and external
        linkage, the behavior is undefined.
        Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
        statements (6.8).

### 6.2.3 [Name spaces of identifiers]

    1   If more than one declaration of a particular identifier is visible at any point in a
        translation unit, the syntactic context disambiguates uses that refer to different entities.
        Thus, there are separate name spaces for various categories of identifiers, as follows:
        — label names (disambiguated by the syntax of the label declaration and use);
        — the tags of structures, unions, and enumerations (disambiguated by following any32)
          of the keywords struct, union, or enum);
        — the members of structures or unions; each structure or union has a separate name
          space for its members (disambiguated by the type of the expression used to access the
          member via the . or -> operator);
        — all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
          enumeration constants).
        Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
        structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
        (6.7.2.3), the goto statement (6.8.6.1).

### 6.2.4 [Storage durations of objects]

    1   An object has a storage duration that determines its lifetime. There are four storage
        durations: static, thread, automatic, and allocated. Allocated storage is described in
        7.22.3.

    2   The lifetime of an object is the portion of program execution during which storage is
        guaranteed to be reserved for it. An object exists, has a constant address,[33] and retains
        its last-stored value throughout its lifetime.[34] If an object is referred to outside of its
        lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
        the object it points to (or just past) reaches the end of its lifetime.

    Footnote 33) The term ‘‘constant address’’ means that two pointers to the object constructed at possibly different
            times will compare equal. The address may be different during two different executions of the same
            program.

    Footnote 34) In the case of a volatile object, the last store need not be explicit in the program.

    3   An object whose identifier is declared without the storage-class specifier
        _Thread_local, and either with external or internal linkage or with the storage-class
        specifier static, has static storage duration. Its lifetime is the entire execution of the
        program and its stored value is initialized only once, prior to program startup.

    4   An object whose identifier is declared with the storage-class specifier _Thread_local
        has thread storage duration. Its lifetime is the entire execution of the thread for which it
        is created, and its stored value is initialized when the thread is started. There is a distinct
        object per thread, and use of the declared name in an expression refers to the object
        associated with the thread evaluating the expression. The result of attempting to
        indirectly access an object with thread storage duration from a thread other than the one
        with which the object is associated is implementation-defined.

    5   An object whose identifier is declared with no linkage and without the storage-class
        specifier static has automatic storage duration, as do some compound literals. The
        result of attempting to indirectly access an object with automatic storage duration from a
        thread other than the one with which the object is associated is implementation-defined.

    6   For such an object that does not have a variable length array type, its lifetime extends
        from entry into the block with which it is associated until execution of that block ends in
        any way. (Entering an enclosed block or calling a function suspends, but does not end,
        execution of the current block.) If the block is entered recursively, a new instance of the
        object is created each time. The initial value of the object is indeterminate. If an
        initialization is specified for the object, it is performed each time the declaration or
        compound literal is reached in the execution of the block; otherwise, the value becomes
        indeterminate each time the declaration is reached.

    7   For such an object that does have a variable length array type, its lifetime extends from
        the declaration of the object until execution of the program leaves the scope of the
        declaration.[35] If the scope is entered recursively, a new instance of the object is created
        each time. The initial value of the object is indeterminate.

    Footnote 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an
            embedded block prior to the declaration, leaves the scope of the declaration.

    8   A non-lvalue expression with structure or union type, where the structure or union
        contains a member with array type (including, recursively, members of all contained
        structures and unions) refers to an object with automatic storage duration and temporary
        lifetime.[36] Its lifetime begins when the expression is evaluated and its initial value is the
        value of the expression. Its lifetime ends when the evaluation of the containing full
        expression or full declarator ends. Any attempt to modify an object with temporary
        lifetime results in undefined behavior.
        Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators
        (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8).

    Footnote 36) The address of such an object is taken implicitly when an array member is accessed.

### 6.2.5 [Types]

    1   The meaning of a value stored in an object or returned by a function is determined by the
        type of the expression used to access it. (An identifier declared to be an object is the
        simplest such expression; the type is specified in the declaration of the identifier.) Types
        are partitioned into object types (types that describe objects) and function types (types
        that describe functions). At various points within a translation unit an object type may be
        incomplete (lacking sufficient information to determine the size of objects of that type) or
        complete (having sufficient information).[37]

    Footnote 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at
            different points within a translation unit.

    2   An object declared as type _Bool is large enough to store the values 0 and 1.

    3   An object declared as type char is large enough to store any member of the basic
        execution character set. If a member of the basic execution character set is stored in a
        char object, its value is guaranteed to be nonnegative. If any other character is stored in
        a char object, the resulting value is implementation-defined but shall be within the range
        of values that can be represented in that type.

    4   There are five standard signed integer types, designated as signed char, short
        int, int, long int, and long long int. (These and other types may be
        designated in several additional ways, as described in 6.7.2.) There may also be
        implementation-defined extended signed integer types.[38] The standard and extended
        signed integer types are collectively called signed integer types.[39]

    Footnote 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as
             described in 7.1.3.

    Footnote 39) Therefore, any statement in this Standard about signed integer types also applies to the extended
             signed integer types.

    5    An object declared as type signed char occupies the same amount of storage as a
         ‘‘plain’’ char object. A ‘‘plain’’ int object has the natural size suggested by the
         architecture of the execution environment (large enough to contain any value in the range
         INT_MIN to INT_MAX as defined in the header <limits.h>).

    6    For each of the signed integer types, there is a corresponding (but different) unsigned
         integer type (designated with the keyword unsigned) that uses the same amount of
         storage (including sign information) and has the same alignment requirements. The type
         _Bool and the unsigned integer types that correspond to the standard signed integer
         types are the standard unsigned integer types. The unsigned integer types that
         correspond to the extended signed integer types are the extended unsigned integer types.
         The standard and extended unsigned integer types are collectively called unsigned integer
         types.[40]

    Footnote 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
             unsigned integer types.

    7    The standard signed integer types and standard unsigned integer types are collectively
         called the standard integer types, the extended signed integer types and extended
         unsigned integer types are collectively called the extended integer types.

    8    For any two integer types with the same signedness and different integer conversion rank
         (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
         subrange of the values of the other type.

    9    The range of nonnegative values of a signed integer type is a subrange of the
         corresponding unsigned integer type, and the representation of the same value in each
         type is the same.[41] A computation involving unsigned operands can never overflow,
         because a result that cannot be represented by the resulting unsigned integer type is
         reduced modulo the number that is one greater than the largest value that can be
         represented by the resulting type.

    Footnote 41) The same representation and alignment requirements are meant to imply interchangeability as
             arguments to functions, return values from functions, and members of unions.

    10   There are three real floating types, designated as float, double, and long
         double.[42] The set of values of the type float is a subset of the set of values of the
         type double; the set of values of the type double is a subset of the set of values of the
         type long double.

    Footnote 42) See ‘‘future language directions’’ (6.11.1).

    11   There are three complex types, designated as float _Complex, double
         _Complex, and long double _Complex.[43] (Complex types are a conditional
         feature that implementations need not support; see 6.10.8.3.) The real floating and
         complex types are collectively called the floating types.

    Footnote 43) A specification for imaginary types is in annex G.

    12   For each floating type there is a corresponding real type, which is always a real floating
         type. For real floating types, it is the same type. For complex types, it is the type given
         by deleting the keyword _Complex from the type name.

    13   Each complex type has the same representation and alignment requirements as an array
         type containing exactly two elements of the corresponding real type; the first element is
         equal to the real part, and the second element to the imaginary part, of the complex
         number.

    14   The type char, the signed and unsigned integer types, and the floating types are
         collectively called the basic types. The basic types are complete object types. Even if the
         implementation defines two or more basic types to have the same representation, they are
         nevertheless different types.[44]

    Footnote 44) An implementation may define new keywords that provide alternative ways to designate a basic (or
             any other) type; this does not violate the requirement that all basic types be different.
             Implementation-defined keywords shall have the form of an identifier reserved for any use as
             described in 7.1.3.

    15   The three types char, signed char, and unsigned char are collectively called
         the character types. The implementation shall define char to have the same range,
         representation, and behavior as either signed char or unsigned char.[45]

    Footnote 45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be
             used to distinguish the two options. Irrespective of the choice made, char is a separate type from the
             other two and is not compatible with either.

    16   An enumeration comprises a set of named integer constant values. Each distinct
         enumeration constitutes a different enumerated type.

    17   The type char, the signed and unsigned integer types, and the enumerated types are
         collectively called integer types. The integer and real floating types are collectively called
         real types.

    18   Integer and floating types are collectively called arithmetic types. Each arithmetic type
         belongs to one type domain: the real type domain comprises the real types, the complex
         type domain comprises the complex types.

    19   The void type comprises an empty set of values; it is an incomplete object type that
         cannot be completed.

    20   Any number of derived types can be constructed from the object and function types, as
         follows:
         — An array type describes a contiguously allocated nonempty set of objects with a
           particular member object type, called the element type. The element type shall be
           complete whenever the array type is specified. Array types are characterized by their
           element type and by the number of elements in the array. An array type is said to be
           derived from its element type, and if its element type is T , the array type is sometimes
           called ‘‘array of T ’’. The construction of an array type from an element type is called
           ‘‘array type derivation’’.
         — A structure type describes a sequentially allocated nonempty set of member objects
           (and, in certain circumstances, an incomplete array), each of which has an optionally
           specified name and possibly distinct type.
         — A union type describes an overlapping nonempty set of member objects, each of
           which has an optionally specified name and possibly distinct type.
         — A function type describes a function with specified return type. A function type is
           characterized by its return type and the number and types of its parameters. A
           function type is said to be derived from its return type, and if its return type is T , the
           function type is sometimes called ‘‘function returning T ’’. The construction of a
           function type from a return type is called ‘‘function type derivation’’.
         — A pointer type may be derived from a function type or an object type, called the
           referenced type. A pointer type describes an object whose value provides a reference
           to an entity of the referenced type. A pointer type derived from the referenced type T
           is sometimes called ‘‘pointer to T ’’. The construction of a pointer type from a
           referenced type is called ‘‘pointer type derivation’’. A pointer type is a complete
           object type.
         — An atomic type describes the type designated by the construct _Atomic ( type-
           name ). (Atomic types are a conditional feature that implementations need not
           support; see 6.10.8.3.)
         These methods of constructing derived types can be applied recursively.

    21   Arithmetic types and pointer types are collectively called scalar types. Array and
         structure types are collectively called aggregate types.[46]

    Footnote 46) Note that aggregate type does not include union type because an object with union type can only
             contain one member at a time.

    22   An array type of unknown size is an incomplete type. It is completed, for an identifier of
         that type, by specifying the size in a later declaration (with internal or external linkage).
         A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete
         type. It is completed, for all declarations of that type, by declaring the same structure or
         union tag with its defining content later in the same scope.

    23   A type has known constant size if the type is not incomplete and is not a variable length
         array type.

    24   Array, function, and pointer types are collectively called derived declarator types. A
         declarator type derivation from a type T is the construction of a derived declarator type
         from T by the application of an array-type, a function-type, or a pointer-type derivation to
         T.

    25   A type is characterized by its type category, which is either the outermost derivation of a
         derived type (as noted above in the construction of derived types), or the type itself if the
         type consists of no derived types.

    26   Any type so far mentioned is an unqualified type. Each unqualified type has several
         qualified versions of its type,[47] corresponding to the combinations of one, two, or all
         three of the const, volatile, and restrict qualifiers. The qualified or unqualified
         versions of a type are distinct types that belong to the same type category and have the
         same representation and alignment requirements.[48] A derived type is not qualified by the
         qualifiers (if any) of the type from which it is derived.

    Footnote 47) See 6.7.3 regarding qualified array and function types.

    Footnote 48) The same representation and alignment requirements are meant to imply interchangeability as
             arguments to functions, return values from functions, and members of unions.

    27   Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier
         designates an atomic type. The size, representation, and alignment of an atomic type
         need not be the same as those of the corresponding unqualified type. Therefore, this
         Standard explicitly uses the phrase ‘‘atomic, qualified or unqualified type’’ whenever the
         atomic version of a type is permitted along with the other qualified versions of a type.
         The phrase ‘‘qualified or unqualified type’’, without specific mention of atomic, does not
         include the atomic types.

    28   A pointer to void shall have the same representation and alignment requirements as a
         pointer to a character type.[48] Similarly, pointers to qualified or unqualified versions of
         compatible types shall have the same representation and alignment requirements. All
         pointers to structure types shall have the same representation and alignment requirements
         as each other. All pointers to union types shall have the same representation and
         alignment requirements as each other. Pointers to other types need not have the same
         representation or alignment requirements.

    Footnote 48) The same representation and alignment requirements are meant to imply interchangeability as
             arguments to functions, return values from functions, and members of unions.

    29   EXAMPLE 1 The type designated as ‘‘float *’’ has type ‘‘pointer to float’’. Its type category is
         pointer, not a floating type. The const-qualified version of this type is designated as ‘‘float * const’’
         whereas the type designated as ‘‘const float *’’ is not a qualified type — its type is ‘‘pointer to const-
         qualified float’’ and is a pointer to a qualified type.

    30   EXAMPLE 2 The type designated as ‘‘struct tag (*[5])(float)’’ has type ‘‘array of pointer to
         function returning struct tag’’. The array has length five and the function has a single parameter of type
         float. Its type category is array.

         Forward references: compatible type and composite type (6.2.7), declarations (6.7).

### 6.2.6 [Representations of types]

### 6.2.6.1 [General]

    1    The representations of all types are unspecified except as stated in this subclause.

    2    Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
         the number, order, and encoding of which are either explicitly specified or
         implementation-defined.

    3    Values stored in unsigned bit-fields and objects of type unsigned char shall be
         represented using a pure binary notation.[49]

    Footnote 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
             represented by successive bits are additive, begin with 1, and are multiplied by successive integral
             powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
             Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
             type unsigned char range from 0 to 2
                                                       CHAR_BIT
                                                                 − 1.

    4    Values stored in non-bit-field objects of any other object type consist of n × CHAR_BIT
         bits, where n is the size of an object of that type, in bytes. The value may be copied into
         an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is
         called the object representation of the value. Values stored in bit-fields consist of m bits,
         where m is the size specified for the bit-field. The object representation is the set of m
         bits the bit-field comprises in the addressable storage unit holding it. Two values (other
         than NaNs) with the same object representation compare equal, but values that compare
         equal may have different object representations.

    5    Certain object representations need not represent a value of the object type. If the stored
         value of an object has such a representation and is read by an lvalue expression that does
         not have character type, the behavior is undefined. If such a representation is produced
         by a side effect that modifies all or any part of the object by an lvalue expression that
         does not have character type, the behavior is undefined.[50] Such a representation is called
         a trap representation.

    Footnote 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined
             behavior, but the value of the variable cannot be used until a proper value is stored in it.

    6    When a value is stored in an object of structure or union type, including in a member
         object, the bytes of the object representation that correspond to any padding bytes take
         unspecified values.[51] The value of a structure or union object is never a trap
        representation, even though the value of a member of the structure or union object may be
        a trap representation.

    Footnote 51) Thus, for example, structure assignment need not copy any padding bits.

    7   When a value is stored in a member of an object of union type, the bytes of the object
        representation that do not correspond to that member but do correspond to other members
        take unspecified values.

    8   Where an operator is applied to a value that has more than one object representation,
        which object representation is used shall not affect the value of the result.[52] Where a
        value is stored in an object using a type that has more than one object representation for
        that value, it is unspecified which representation is used, but a trap representation shall
        not be generated.

    Footnote 52) It is possible for objects x and y with the same effective type T to have the same value when they are
            accessed as objects of type T, but to have different values in other contexts. In particular, if == is
            defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
            Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
            on values of type T may distinguish between them.

    9   Loads and stores of objects with                             atomic      types      are     done      with
        memory_order_seq_cst semantics.
        Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
        designators (6.3.2.1), order and consistency (7.17.3).

### 6.2.6.2 [Integer types]

    1   For unsigned integer types other than unsigned char, the bits of the object
        representation shall be divided into two groups: value bits and padding bits (there need
        not be any of the latter). If there are N value bits, each bit shall represent a different
        power of 2 between 1 and 2 N −1 , so that objects of that type shall be capable of
        representing values from 0 to 2 N − 1 using a pure binary representation; this shall be
        known as the value representation. The values of any padding bits are unspecified.[53]

    Footnote 53) Some combinations of padding bits might generate trap representations, for example, if one padding
            bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
            representation other than as part of an exceptional condition such as an overflow, and this cannot occur
            with unsigned types. All other combinations of padding bits are alternative object representations of
            the value specified by the value bits.

    2   For signed integer types, the bits of the object representation shall be divided into three
        groups: value bits, padding bits, and the sign bit. There need not be any padding bits;
        signed char shall not have any padding bits. There shall be exactly one sign bit.
        Each bit that is a value bit shall have the same value as the same bit in the object
        representation of the corresponding unsigned type (if there are M value bits in the signed
        type and N in the unsigned type, then M ≤ N ). If the sign bit is zero, it shall not affect
        the resulting value. If the sign bit is one, the value shall be modified in one of the
        following ways:
        — the corresponding value with sign bit 0 is negated (sign and magnitude);
        — the sign bit has the value −(2 M ) (two’s complement);
        — the sign bit has the value −(2 M − 1) (ones’ complement).
        Which of these applies is implementation-defined, as is whether the value with sign bit 1
        and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones’
        complement), is a trap representation or a normal value. In the case of sign and
        magnitude and ones’ complement, if this representation is a normal value it is called a
        negative zero.

    3   If the implementation supports negative zeros, they shall be generated only by:
        — the &, |, ^, ~, <<, and >> operators with operands that produce such a value;
        — the +, -, *, /, and % operators where one operand is a negative zero and the result is
          zero;
        — compound assignment operators based on the above cases.
        It is unspecified whether these cases actually generate a negative zero or a normal zero,
        and whether a negative zero becomes a normal zero when stored in an object.

    4   If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,
        and >> operators with operands that would produce such a value is undefined.

    5   The values of any padding bits are unspecified.[54] A valid (non-trap) object representation
        of a signed integer type where the sign bit is zero is a valid object representation of the
        corresponding unsigned type, and shall represent the same value. For any integer type,
        the object representation where all the bits are zero shall be a representation of the value
        zero in that type.

    Footnote 54) Some combinations of padding bits might generate trap representations, for example, if one padding
            bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
            representation other than as part of an exceptional condition such as an overflow. All other
            combinations of padding bits are alternative object representations of the value specified by the value
            bits.

    6   The precision of an integer type is the number of bits it uses to represent values,
        excluding any sign and padding bits. The width of an integer type is the same but
        including any sign bit; thus for unsigned integer types the two values are the same, while
        for signed integer types the width is one greater than the precision.

### 6.2.7 [Compatible type and composite type]

    1   Two types have compatible type if their types are the same. Additional rules for
        determining whether two types are compatible are described in 6.7.2 for type specifiers,
        in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.[55] Moreover, two structure,
        union, or enumerated types declared in separate translation units are compatible if their
        tags and members satisfy the following requirements: If one is declared with a tag, the
        other shall be declared with the same tag. If both are completed anywhere within their
        respective translation units, then the following additional requirements apply: there shall
        be a one-to-one correspondence between their members such that each pair of
        corresponding members are declared with compatible types; if one member of the pair is
        declared with an alignment specifier, the other is declared with an equivalent alignment
        specifier; and if one member of the pair is declared with a name, the other is declared
        with the same name. For two structures, corresponding members shall be declared in the
        same order. For two structures or unions, corresponding bit-fields shall have the same
        widths. For two enumerations, corresponding members shall have the same values.

    Footnote 55) Two types need not be identical to be compatible.

    2   All declarations that refer to the same object or function shall have compatible type;
        otherwise, the behavior is undefined.

    3   A composite type can be constructed from two types that are compatible; it is a type that
        is compatible with both of the two types and satisfies the following conditions:
        — If both types are array types, the following rules are applied:
              • If one type is an array of known constant size, the composite type is an array of
                that size.
              • Otherwise, if one type is a variable length array whose size is specified by an
                expression that is not evaluated, the behavior is undefined.
              • Otherwise, if one type is a variable length array whose size is specified, the
                composite type is a variable length array of that size.
              • Otherwise, if one type is a variable length array of unspecified size, the composite
                type is a variable length array of unspecified size.
              • Otherwise, both types are arrays of unknown size and the composite type is an
                array of unknown size.
            The element type of the composite type is the composite type of the two element
            types.
        — If only one type is a function type with a parameter type list (a function prototype),
          the composite type is a function prototype with the parameter type list.
        — If both types are function types with parameter type lists, the type of each parameter
          in the composite parameter type list is the composite type of the corresponding
          parameters.
        These rules apply recursively to the types from which the two types are derived.

    4   For an identifier with internal or external linkage declared in a scope in which a prior
        declaration of that identifier is visible,[56] if the prior declaration specifies internal or
        external linkage, the type of the identifier at the later declaration becomes the composite
        type.
        Forward references: array declarators (6.7.6.2).

    Footnote 56) As specified in 6.2.1, the later declaration might hide the prior declaration.

    5   EXAMPLE        Given the following two file scope declarations:
                 int f(int (*)(), double (*)[3]);
                 int f(int (*)(char *), double (*)[]);
        The resulting composite type for the function is:
                 int f(int (*)(char *), double (*)[3]);

### 6.2.8 [Alignment of objects]

    1   Complete object types have alignment requirements which place restrictions on the
        addresses at which objects of that type may be allocated. An alignment is an
        implementation-defined integer value representing the number of bytes between
        successive addresses at which a given object can be allocated. An object type imposes an
        alignment requirement on every object of that type: stricter alignment can be requested
        using the _Alignas keyword.

    2   A fundamental alignment is represented by an alignment less than or equal to the greatest
        alignment supported by the implementation in all contexts, which is equal to
        _Alignof (max_align_t).

    3   An extended alignment is represented by an alignment greater than
        _Alignof (max_align_t). It is implementation-defined whether any extended
        alignments are supported and the contexts in which they are supported. A type having an
        extended alignment requirement is an over-aligned type.[57]

    Footnote 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended
            alignment has been applied.

    4   Alignments are represented as values of the type size_t. Valid alignments include only
        those values returned by an _Alignof expression for fundamental types, plus an
        additional implementation-defined set of values, which may be empty. Every valid
        alignment value shall be a nonnegative integral power of two.

    5   Alignments have an order from weaker to stronger or stricter alignments. Stricter
        alignments have larger alignment values. An address that satisfies an alignment
        requirement also satisfies any weaker valid alignment requirement.

    6   The alignment requirement of a complete type can be queried using an _Alignof
        expression. The types char, signed char, and unsigned char shall have the
        weakest alignment requirement.

    7   Comparing alignments is meaningful and provides the obvious results:
        — Two alignments are equal when their numeric values are equal.
        — Two alignments are different when their numeric values are not equal.
        — When an alignment is larger than another it represents a stricter alignment.

### 6.3 [Conversions]

    1   Several operators convert operand values from one type to another automatically. This
        subclause specifies the result required from such an implicit conversion, as well as those
        that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
        the conversions performed by most ordinary operators; it is supplemented as required by
        the discussion of each operator in 6.5.

    2   Conversion of an operand value to a compatible type causes no change to the value or the
        representation.
        Forward references: cast operators (6.5.4).

### 6.3.1 [Arithmetic operands]

### 6.3.1.1 [Boolean, characters, and integers]

    1   Every integer type has an integer conversion rank defined as follows:
        — No two signed integer types shall have the same rank, even if they have the same
          representation.
        — The rank of a signed integer type shall be greater than the rank of any signed integer
          type with less precision.
        — The rank of long long int shall be greater than the rank of long int, which
          shall be greater than the rank of int, which shall be greater than the rank of short
          int, which shall be greater than the rank of signed char.
        — The rank of any unsigned integer type shall equal the rank of the corresponding
          signed integer type, if any.
        — The rank of any standard integer type shall be greater than the rank of any extended
          integer type with the same width.
        — The rank of char shall equal the rank of signed char and unsigned char.
        — The rank of _Bool shall be less than the rank of all other standard integer types.
        — The rank of any enumerated type shall equal the rank of the compatible integer type
          (see 6.7.2.2).
        — The rank of any extended signed integer type relative to another extended signed
          integer type with the same precision is implementation-defined, but still subject to the
          other rules for determining the integer conversion rank.
        — For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has
          greater rank than T3, then T1 has greater rank than T3.

    2   The following may be used in an expression wherever an int or unsigned int may
        be used:
        — An object or expression with an integer type (other than int or unsigned int)
          whose integer conversion rank is less than or equal to the rank of int and
          unsigned int.
        — A bit-field of type _Bool, int, signed int, or unsigned int.
        If an int can represent all values of the original type (as restricted by the width, for a
        bit-field), the value is converted to an int; otherwise, it is converted to an unsigned
        int. These are called the integer promotions.[58] All other types are unchanged by the
        integer promotions.

    Footnote 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
            argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the
            shift operators, as specified by their respective subclauses.

    3   The integer promotions preserve value including sign. As discussed earlier, whether a
        ‘‘plain’’ char is treated as signed is implementation-defined.
        Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
        (6.7.2.1).

### 6.3.1.2 [Boolean type]

    1   When any scalar value is converted to _Bool, the result is 0 if the value compares equal
        to 0; otherwise, the result is 1.[59]

    Footnote 59) NaNs do not compare equal to 0 and thus convert to 1.

### 6.3.1.3 [Signed and unsigned integers]

    1   When a value with integer type is converted to another integer type other than _Bool, if
        the value can be represented by the new type, it is unchanged.

    2   Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
        subtracting one more than the maximum value that can be represented in the new type
        until the value is in the range of the new type.[60]

    Footnote 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.

    3   Otherwise, the new type is signed and the value cannot be represented in it; either the
        result is implementation-defined or an implementation-defined signal is raised.

### 6.3.1.4 [Real floating and integer]

    1   When a finite value of real floating type is converted to an integer type other than _Bool,
        the fractional part is discarded (i.e., the value is truncated toward zero). If the value of
        the integral part cannot be represented by the integer type, the behavior is undefined.[61]

    Footnote 61) The remaindering operation performed when a value of integer type is converted to unsigned type
            need not be performed when a value of real floating type is converted to unsigned type. Thus, the
            range of portable real floating values is (−1, Utype_MAX+1).

    2   When a value of integer type is converted to a real floating type, if the value being
        converted can be represented exactly in the new type, it is unchanged. If the value being
        converted is in the range of values that can be represented but cannot be represented
        exactly, the result is either the nearest higher or nearest lower representable value, chosen
        in an implementation-defined manner. If the value being converted is outside the range of
        values that can be represented, the behavior is undefined. Results of some implicit
        conversions may be represented in greater range and precision than that required by the
        new type (see 6.3.1.8 and 6.8.6.4).

### 6.3.1.5 [Real floating types]

    1   When a value of real floating type is converted to a real floating type, if the value being
        converted can be represented exactly in the new type, it is unchanged. If the value being
        converted is in the range of values that can be represented but cannot be represented
        exactly, the result is either the nearest higher or nearest lower representable value, chosen
        in an implementation-defined manner. If the value being converted is outside the range of
        values that can be represented, the behavior is undefined. Results of some implicit
        conversions may be represented in greater range and precision than that required by the
        new type (see 6.3.1.8 and 6.8.6.4).

### 6.3.1.6 [Complex types]

    1   When a value of complex type is converted to another complex type, both the real and
        imaginary parts follow the conversion rules for the corresponding real types.

### 6.3.1.7 [Real and complex]

    1   When a value of real type is converted to a complex type, the real part of the complex
        result value is determined by the rules of conversion to the corresponding real type and
        the imaginary part of the complex result value is a positive zero or an unsigned zero.

    2   When a value of complex type is converted to a real type, the imaginary part of the
        complex value is discarded and the value of the real part is converted according to the
        conversion rules for the corresponding real type.

### 6.3.1.8 [Usual arithmetic conversions]

    1   Many operators that expect operands of arithmetic type cause conversions and yield result
        types in a similar way. The purpose is to determine a common real type for the operands
        and result. For the specified operands, each operand is converted, without change of type
        domain, to a type whose corresponding real type is the common real type. Unless
        explicitly stated otherwise, the common real type is also the corresponding real type of
        the result, whose type domain is the type domain of the operands if they are the same,
        and complex otherwise. This pattern is called the usual arithmetic conversions:
              First, if the corresponding real type of either operand is long double, the other
              operand is converted, without change of type domain, to a type whose
               corresponding real type is long double.
               Otherwise, if the corresponding real type of either operand is double, the other
               operand is converted, without change of type domain, to a type whose
               corresponding real type is double.
               Otherwise, if the corresponding real type of either operand is float, the other
               operand is converted, without change of type domain, to a type whose
               corresponding real type is float.[62]
               Otherwise, the integer promotions are performed on both operands. Then the
               following rules are applied to the promoted operands:
                      If both operands have the same type, then no further conversion is needed.
                      Otherwise, if both operands have signed integer types or both have unsigned
                      integer types, the operand with the type of lesser integer conversion rank is
                      converted to the type of the operand with greater rank.
                      Otherwise, if the operand that has unsigned integer type has rank greater or
                      equal to the rank of the type of the other operand, then the operand with
                      signed integer type is converted to the type of the operand with unsigned
                      integer type.
                      Otherwise, if the type of the operand with signed integer type can represent
                      all of the values of the type of the operand with unsigned integer type, then
                      the operand with unsigned integer type is converted to the type of the
                      operand with signed integer type.
                      Otherwise, both operands are converted to the unsigned integer type
                      corresponding to the type of the operand with signed integer type.

    Footnote 62) For example, addition of a double _Complex and a float entails just the conversion of the
            float operand to double (and yields a double _Complex result).

    2   The values of floating operands and of the results of floating expressions may be
        represented in greater range and precision than that required by the type; the types are not
        changed thereby.[63]

    Footnote 63) The cast and assignment operators are still required to remove extra range and precision.

### 6.3.2 [Other operands]

### 6.3.2.1 [Lvalues, arrays, and function designators]

    1   An lvalue is an expression (with an object type other than void) that potentially
        designates an object;[64] if an lvalue does not designate an object when it is evaluated, the
        behavior is undefined. When an object is said to have a particular type, the type is
        specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that
        does not have array type, does not have an incomplete type, does not have a const-
        qualified type, and if it is a structure or union, does not have any member (including,
        recursively, any member or element of all contained aggregates or unions) with a const-
        qualified type.

    Footnote 64) The name ‘‘lvalue’’ comes originally from the assignment expression E1 = E2, in which the left
            operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an
            object ‘‘locator value’’. What is sometimes called ‘‘rvalue’’ is in this International Standard described
            as the ‘‘value of an expression’’.
             An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary
             expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.

    2   Except when it is the operand of the sizeof operator, the _Alignof operator, the
        unary & operator, the ++ operator, the -- operator, or the left operand of the . operator
        or an assignment operator, an lvalue that does not have array type is converted to the
        value stored in the designated object (and is no longer an lvalue); this is called lvalue
        conversion. If the lvalue has qualified type, the value has the unqualified version of the
        type of the lvalue; additionally, if the lvalue has atomic type, the value has the non-atomic
        version of the type of the lvalue; otherwise, the value has the type of the lvalue. If the
        lvalue has an incomplete type and does not have array type, the behavior is undefined. If
        the lvalue designates an object of automatic storage duration that could have been
        declared with the register storage class (never had its address taken), and that object
        is uninitialized (not declared with an initializer and no assignment to it has been
        performed prior to use), the behavior is undefined.

    3   Except when it is the operand of the sizeof operator, the _Alignof operator, or the
        unary & operator, or is a string literal used to initialize an array, an expression that has
        type ‘‘array of type’’ is converted to an expression with type ‘‘pointer to type’’ that points
        to the initial element of the array object and is not an lvalue. If the array object has
        register storage class, the behavior is undefined.

    4   A function designator is an expression that has function type. Except when it is the
        operand of the sizeof operator, the _Alignof operator,[65] or the unary & operator, a
        function designator with type ‘‘function returning type’’ is converted to an expression that
        has type ‘‘pointer to function returning type’’.
        Forward references: address and indirection operators (6.5.3.2), assignment operators
        (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix
        increment and decrement operators (6.5.2.4), prefix increment and decrement operators
        (6.5.3.1), the sizeof and _Alignof operators (6.5.3.4), structure and union members
        (6.5.2.3).

    Footnote 65) Because this conversion does not occur, the operand of the sizeof or _Alignof operator remains
            a function designator and violates the constraints in 6.5.3.4.

### 6.3.2.2 [void]

    1   The (nonexistent) value of a void expression (an expression that has type void) shall not
        be used in any way, and implicit or explicit conversions (except to void) shall not be
        applied to such an expression. If an expression of any other type is evaluated as a void
        expression, its value or designator is discarded. (A void expression is evaluated for its
        side effects.)

### 6.3.2.3 [Pointers]

    1   A pointer to void may be converted to or from a pointer to any object type. A pointer to
        any object type may be converted to a pointer to void and back again; the result shall
        compare equal to the original pointer.

    2   For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to
        the q-qualified version of the type; the values stored in the original and converted pointers
        shall compare equal.

    3   An integer constant expression with the value 0, or such an expression cast to type
        void *, is called a null pointer constant.[66] If a null pointer constant is converted to a
        pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
        to a pointer to any object or function.

    Footnote 66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19.

    4   Conversion of a null pointer to another pointer type yields a null pointer of that type.
        Any two null pointers shall compare equal.

    5   An integer may be converted to any pointer type. Except as previously specified, the
        result is implementation-defined, might not be correctly aligned, might not point to an
        entity of the referenced type, and might be a trap representation.[67]

    Footnote 67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to
            be consistent with the addressing structure of the execution environment.

    6   Any pointer type may be converted to an integer type. Except as previously specified, the
        result is implementation-defined. If the result cannot be represented in the integer type,
        the behavior is undefined. The result need not be in the range of values of any integer
        type.

    7   A pointer to an object type may be converted to a pointer to a different object type. If the
        resulting pointer is not correctly aligned[68] for the referenced type, the behavior is
        undefined. Otherwise, when converted back again, the result shall compare equal to the
        original pointer. When a pointer to an object is converted to a pointer to a character type,
        the result points to the lowest addressed byte of the object. Successive increments of the
        result, up to the size of the object, yield pointers to the remaining bytes of the object.

    Footnote 68) In general, the concept ‘‘correctly aligned’’ is transitive: if a pointer to type A is correctly aligned for a
            pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is
            correctly aligned for a pointer to type C.

    8   A pointer to a function of one type may be converted to a pointer to a function of another
        type and back again; the result shall compare equal to the original pointer. If a converted
        pointer is used to call a function whose type is not compatible with the referenced type,
        the behavior is undefined.
        Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
        capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1).

### 6.4 [Lexical elements]

    1 Syntax
                token:
                          keyword
                          identifier
                          constant
                          string-literal
                          punctuator
                 preprocessing-token:
                        header-name
                        identifier
                        pp-number
                        character-constant
                        string-literal
                        punctuator
                        each non-white-space character that cannot be one of the above
        Constraints

    2   Each preprocessing token that is converted to a token shall have the lexical form of a
        keyword, an identifier, a constant, a string literal, or a punctuator.
        Semantics

    3   A token is the minimal lexical element of the language in translation phases 7 and 8. The
        categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
        A preprocessing token is the minimal lexical element of the language in translation
        phases 3 through 6. The categories of preprocessing tokens are: header names,
        identifiers, preprocessing numbers, character constants, string literals, punctuators, and
        single non-white-space characters that do not lexically match the other preprocessing
        token categories.[69] If a ' or a " character matches the last category, the behavior is
        undefined. Preprocessing tokens can be separated by white space; this consists of
        comments (described later), or white-space characters (space, horizontal tab, new-line,
        vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
        during translation phase 4, white space (or the absence thereof) serves as more than
        preprocessing token separation. White space may appear within a preprocessing token
        only as part of a header name or between the quotation characters in a character constant
        or string literal.

    Footnote 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
            occur in source files.

    4   If the input stream has been parsed into preprocessing tokens up to a given character, the
        next preprocessing token is the longest sequence of characters that could constitute a
        preprocessing token. There is one exception to this rule: header name preprocessing
        tokens are recognized only within #include preprocessing directives and in
        implementation-defined locations within #pragma directives. In such contexts, a
        sequence of characters that could be either a header name or a string literal is recognized
        as the former.

    5   EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
        valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
        might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
        fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
        not E is a macro name.

    6   EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
        increment operators, even though the parse x ++ + ++ y might yield a correct expression.

        Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
        floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
        increment and decrement operators (6.5.2.4), prefix increment and decrement operators
        (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals
        (6.4.5).

### 6.4.1 [Keywords]

    1 Syntax
                keyword: one of
                       auto                         ∗ if                             unsigned
                       break                          inline                         void
                       case                           int                            volatile
                       char                           long                           while
                       const                          register                       _Alignas
                       continue                       restrict                       _Alignof
                       default                        return                         _Atomic
                       do                             short                          _Bool
                       double                         signed                         _Complex
                       else                           sizeof                         _Generic
                       enum                           static                         _Imaginary
                       extern                         struct                         _Noreturn
                       float                          switch                         _Static_assert
                       for                            typedef                        _Thread_local
                       goto                           union
        Semantics

    2   The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
        specifying imaginary types.[70]

    Footnote 70) One possible specification for imaginary types appears in annex G.

### 6.4.2 [Identifiers]

### 6.4.2.1 [General]

    1 Syntax
                identifier:
                         identifier-nondigit
                         identifier identifier-nondigit
                         identifier digit
                 identifier-nondigit:
                         nondigit
                         universal-character-name
                         other implementation-defined characters
                 nondigit: one of
                        _ a b            c    d    e    f     g    h    i    j     k    l    m
                            n o          p    q    r    s     t    u    v    w     x    y    z
                            A B          C    D    E    F     G    H    I    J     K    L    M
                            N O          P    Q    R    S     T    U    V    W     X    Y    Z
                 digit: one of
                        0 1        2     3    4    5    6     7    8    9
        Semantics

    2   An identifier is a sequence of nondigit characters (including the underscore _, the
        lowercase and uppercase Latin letters, and other characters) and digits, which designates
        one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
        There is no specific limit on the maximum length of an identifier.

    3   Each universal character name in an identifier shall designate a character whose encoding
        in ISO/IEC 10646 falls into one of the ranges specified in D.1.[71] The initial character
        shall not be a universal character name designating a character whose encoding falls into
        one of the ranges specified in D.2. An implementation may allow multibyte characters
        that are not part of the basic source character set to appear in identifiers; which characters
        and their correspondence to universal character names is implementation-defined.

    Footnote 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character
            name may be used in forming valid external identifiers. For example, some otherwise unused
            character or sequence of characters may be used to encode the \u in a universal character name.
            Extended characters may produce a long external identifier.

    4   When preprocessing tokens are converted to tokens during translation phase 7, if a
        preprocessing token could be converted to either a keyword or an identifier, it is converted
        to a keyword.
        Implementation limits

    5   As discussed in 5.2.4.1, an implementation may limit the number of significant initial
        characters in an identifier; the limit for an external name (an identifier that has external
        linkage) may be more restrictive than that for an internal name (a macro name or an
        identifier that does not have external linkage). The number of significant characters in an
        identifier is implementation-defined.

    6   Any identifiers that differ in a significant character are different identifiers. If two
        identifiers differ only in nonsignificant characters, the behavior is undefined.
        Forward references: universal character names (6.4.3), macro replacement (6.10.3).

### 6.4.2.2 [Predefined identifiers]

    1 Semantics
       The identifier _ _func_ _ shall be implicitly declared by the translator as if,
        immediately following the opening brace of each function definition, the declaration
                 static const char _ _func_ _[] = "function-name";
        appeared, where function-name is the name of the lexically-enclosing function.[72]

    Footnote 72) Since the name _ _func_ _ is reserved for any use by the implementation (7.1.3), if any other
            identifier is explicitly declared using the name _ _func_ _, the behavior is undefined.

    2   This name is encoded as if the implicit declaration had been written in the source
        character set and then translated into the execution character set as indicated in translation
        phase 5.

    3   EXAMPLE        Consider the code fragment:
                 #include <stdio.h>
                 void myfunc(void)
                 {
                       printf("%s\n", _ _func_ _);
                       /* ... */
                 }
        Each time the function is called, it will print to the standard output stream:
                 myfunc

        Forward references: function definitions (6.9.1).

### 6.4.3 [Universal character names]

    1 Syntax
                universal-character-name:
                        \u hex-quad
                        \U hex-quad hex-quad
                 hex-quad:
                        hexadecimal-digit hexadecimal-digit
                                     hexadecimal-digit hexadecimal-digit
        Constraints

    2   A universal character name shall not specify a character whose short identifier is less than
        00A0 other than 0024 ($), 0040 (@), or 0060 (‘), nor one in the range D800 through
        DFFF inclusive.[73]
        Description

    Footnote 73) The disallowed characters are the characters in the basic character set and the code positions reserved
            by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
            UTF−16).

    3   Universal character names may be used in identifiers, character constants, and string
        literals to designate characters that are not in the basic character set.
        Semantics

    4   The universal character name \Unnnnnnnn designates the character whose eight-digit
        short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.[74] Similarly, the universal
        character name \unnnn designates the character whose four-digit short identifier is nnnn
        (and whose eight-digit short identifier is 0000nnnn).

    Footnote 74) Short identifiers for characters were first specified in ISO/IEC 10646−1/AMD9:1997.

### 6.4.4 [Constants]

    1 Syntax
                constant:
                        integer-constant
                        floating-constant
                        enumeration-constant
                        character-constant
        Constraints

    2   Each constant shall have a type and the value of a constant shall be in the range of
        representable values for its type.
        Semantics

    3   Each constant has a type, determined by its form and value, as detailed later.

### 6.4.4.1 [Integer constants]

    1 Syntax
                integer-constant:
                         decimal-constant integer-suffixopt
                         octal-constant integer-suffixopt
                         hexadecimal-constant integer-suffixopt
                 decimal-constant:
                       nonzero-digit
                       decimal-constant digit
                 octal-constant:
                        0
                        octal-constant octal-digit
                 hexadecimal-constant:
                       hexadecimal-prefix hexadecimal-digit
                       hexadecimal-constant hexadecimal-digit
                 hexadecimal-prefix: one of
                       0x 0X
                 nonzero-digit: one of
                        1 2 3 4           5    6     7   8   9
                 octal-digit: one of
                         0 1 2 3          4    5     6   7
               hexadecimal-digit: one of
                     0 1 2 3 4                5    6    7    8   9
                     a b c d e                f
                     A B C D E                F
               integer-suffix:
                       unsigned-suffix long-suffixopt
                       unsigned-suffix long-long-suffix
                       long-suffix unsigned-suffixopt
                       long-long-suffix unsigned-suffixopt
               unsigned-suffix: one of
                      u U
               long-suffix: one of
                      l L
               long-long-suffix: one of
                      ll LL
        Description

    2   An integer constant begins with a digit, but has no period or exponent part. It may have a
        prefix that specifies its base and a suffix that specifies its type.

    3   A decimal constant begins with a nonzero digit and consists of a sequence of decimal
        digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the
        digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
        by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
        10 through 15 respectively.
        Semantics

    4   The value of a decimal constant is computed base 10; that of an octal constant, base 8;
        that of a hexadecimal constant, base 16. The lexically first digit is the most significant.

    5   The type of an integer constant is the first of the corresponding list in which its value can
        be represented.
                                                                         Octal or Hexadecimal
        Suffix                      Decimal Constant                           Constant

        none                int                                    int
                            long int                               unsigned int
                            long long int                          long int
                                                                   unsigned long int
                                                                   long long int
                                                                   unsigned long long int

        u or U              unsigned int                           unsigned int
                            unsigned long int                      unsigned long int
                            unsigned long long int                 unsigned long long int

        l or L              long int                               long int
                            long long int                          unsigned long int
                                                                   long long int
                                                                   unsigned long long int

        Both u or U         unsigned long int                      unsigned long int
        and l or L          unsigned long long int                 unsigned long long int

        ll or LL            long long int                          long long int
                                                                   unsigned long long int

        Both u or U         unsigned long long int                 unsigned long long int
        and ll or LL

    6   If an integer constant cannot be represented by any type in its list, it may have an
        extended integer type, if the extended integer type can represent its value. If all of the
        types in the list for the constant are signed, the extended integer type shall be signed. If
        all of the types in the list for the constant are unsigned, the extended integer type shall be
        unsigned. If the list contains both signed and unsigned types, the extended integer type
        may be signed or unsigned. If an integer constant cannot be represented by any type in
        its list and has no extended integer type, then the integer constant has no type.

### 6.4.4.2 [Floating constants]

    1 Syntax
                floating-constant:
                         decimal-floating-constant
                         hexadecimal-floating-constant
                 decimal-floating-constant:
                       fractional-constant exponent-partopt floating-suffixopt
                       digit-sequence exponent-part floating-suffixopt
                 hexadecimal-floating-constant:
                       hexadecimal-prefix hexadecimal-fractional-constant
                                       binary-exponent-part floating-suffixopt
                       hexadecimal-prefix hexadecimal-digit-sequence
                                       binary-exponent-part floating-suffixopt
                 fractional-constant:
                         digit-sequenceopt . digit-sequence
                         digit-sequence .
                 exponent-part:
                       e signopt digit-sequence
                       E signopt digit-sequence
                 sign: one of
                        + -
                 digit-sequence:
                         digit
                         digit-sequence digit
                 hexadecimal-fractional-constant:
                       hexadecimal-digit-sequenceopt .
                                      hexadecimal-digit-sequence
                       hexadecimal-digit-sequence .
                 binary-exponent-part:
                        p signopt digit-sequence
                        P signopt digit-sequence
                 hexadecimal-digit-sequence:
                       hexadecimal-digit
                       hexadecimal-digit-sequence hexadecimal-digit
                 floating-suffix: one of
                         f l F L
        Description

    2   A floating constant has a significand part that may be followed by an exponent part and a
        suffix that specifies its type. The components of the significand part may include a digit
        sequence representing the whole-number part, followed by a period (.), followed by a
        digit sequence representing the fraction part. The components of the exponent part are an
        e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
        Either the whole-number part or the fraction part has to be present; for decimal floating
        constants, either the period or the exponent part has to be present.
        Semantics

    3   The significand part is interpreted as a (decimal or hexadecimal) rational number; the
        digit sequence in the exponent part is interpreted as a decimal integer. For decimal
        floating constants, the exponent indicates the power of 10 by which the significand part is
        to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
        by which the significand part is to be scaled. For decimal floating constants, and also for
        hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
        the nearest representable value, or the larger or smaller representable value immediately
        adjacent to the nearest representable value, chosen in an implementation-defined manner.
        For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is
        correctly rounded.

    4   An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
        type float. If suffixed by the letter l or L, it has type long double.

    5   Floating constants are converted to internal format as if at translation-time. The
        conversion of a floating constant shall not raise an exceptional condition or a floating-
        point exception at execution time. All floating constants of the same source form[75] shall
        convert to the same internal format with the same value.
        Recommended practice

    Footnote 75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not
            convert to the same internal format and value.

    6   The implementation should produce a diagnostic message if a hexadecimal constant
        cannot be represented exactly in its evaluation format; the implementation should then
        proceed with the translation of the program.

    7   The translation-time conversion of floating constants should match the execution-time
        conversion of character strings by library functions, such as strtod, given matching
        inputs suitable for both conversions, the same result format, and default execution-time
        rounding.[76]

    Footnote 76) The specification for the library functions recommends more accurate conversion than required for
            floating constants (see 7.22.1.3).

### 6.4.4.3 [Enumeration constants]

    1 Syntax
                enumeration-constant:
                       identifier
        Semantics

    2   An identifier declared as an enumeration constant has type int.
        Forward references: enumeration specifiers (6.7.2.2).

### 6.4.4.4 [Character constants]

    1 Syntax
                character-constant:
                        ' c-char-sequence '
                        L' c-char-sequence '
                        u' c-char-sequence '
                        U' c-char-sequence '
                 c-char-sequence:
                        c-char
                        c-char-sequence c-char
                 c-char:
                           any member of the source character set except
                                        the single-quote ', backslash \, or new-line character
                           escape-sequence
                 escape-sequence:
                        simple-escape-sequence
                        octal-escape-sequence
                        hexadecimal-escape-sequence
                        universal-character-name
                 simple-escape-sequence: one of
                        \' \" \? \\
                        \a \b \f \n \r                  \t    \v
                 octal-escape-sequence:
                         \ octal-digit
                         \ octal-digit octal-digit
                         \ octal-digit octal-digit octal-digit
               hexadecimal-escape-sequence:
                     \x hexadecimal-digit
                     hexadecimal-escape-sequence hexadecimal-digit
        Description

    2   An integer character constant is a sequence of one or more multibyte characters enclosed
        in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
        letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are
        any members of the source character set; they are mapped in an implementation-defined
        manner to members of the execution character set.

    3   The single-quote ', the double-quote ", the question-mark ?, the backslash \, and
        arbitrary integer values are representable according to the following table of escape
        sequences:
              single quote '            \'
              double quote "            \"
              question mark ?           \?
              backslash \               \\
              octal character           \octal digits
              hexadecimal character     \x hexadecimal digits

    4   The double-quote " and question-mark ? are representable either by themselves or by the
        escape sequences \" and \?, respectively, but the single-quote ' and the backslash \
        shall be represented, respectively, by the escape sequences \' and \\.

    5   The octal digits that follow the backslash in an octal escape sequence are taken to be part
        of the construction of a single character for an integer character constant or of a single
        wide character for a wide character constant. The numerical value of the octal integer so
        formed specifies the value of the desired character or wide character.

    6   The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape
        sequence are taken to be part of the construction of a single character for an integer
        character constant or of a single wide character for a wide character constant. The
        numerical value of the hexadecimal integer so formed specifies the value of the desired
        character or wide character.

    7   Each octal or hexadecimal escape sequence is the longest sequence of characters that can
        constitute the escape sequence.

    8   In addition, characters not in the basic character set are representable by universal
        character names and certain nongraphic characters are representable by escape sequences
        consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
        and \v.[77]
         Constraints

    Footnote 77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
             the result is not a token and a diagnostic is required. See ‘‘future language directions’’ (6.11.4).

    9    The value of an octal or hexadecimal escape sequence shall be in the range of
         representable values for the corresponding type:
                Prefix     Corresponding Type
                none       unsigned char
                L          the unsigned type corresponding to wchar_t
                u          char16_t
                U          char32_t
         Semantics

    10   An integer character constant has type int. The value of an integer character constant
         containing a single character that maps to a single-byte execution character is the
         numerical value of the representation of the mapped character interpreted as an integer.
         The value of an integer character constant containing more than one character (e.g.,
         'ab'), or containing a character or escape sequence that does not map to a single-byte
         execution character, is implementation-defined. If an integer character constant contains
         a single character or escape sequence, its value is the one that results when an object with
         type char whose value is that of the single character or escape sequence is converted to
         type int.

    11   A wide character constant prefixed by the letter L has type wchar_t, an integer type
         defined in the <stddef.h> header; a wide character constant prefixed by the letter u or
         U has type char16_t or char32_t, respectively, unsigned integer types defined in the
         <uchar.h> header. The value of a wide character constant containing a single
         multibyte character that maps to a single member of the extended execution character set
         is the wide character corresponding to that multibyte character, as defined by the
         mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an
         implementation-defined current locale. The value of a wide character constant containing
         more than one multibyte character or a single multibyte character that maps to multiple
         members of the extended execution character set, or containing a multibyte character or
         escape sequence not represented in the extended execution character set, is
         implementation-defined.

    12   EXAMPLE 1       The construction '\0' is commonly used to represent the null character.

    13   EXAMPLE 2 Consider implementations that use two’s complement representation for integers and eight
         bits for objects that have type char. In an implementation in which type char has the same range of
         values as signed char, the integer character constant '\xFF' has the value −1; if type char has the
         same range of values as unsigned char, the character constant '\xFF' has the value +255.

    14   EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
         specifies an integer character constant containing only one character, since a hexadecimal escape sequence
         is terminated only by a non-hexadecimal character. To specify an integer character constant containing the
         two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
         escape sequence is terminated after three octal digits. (The value of this two-character integer character
         constant is implementation-defined.)

    15   EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
         L'\1234' specifies the implementation-defined value that results from the combination of the values
         0123 and '4'.

         Forward references: common definitions <stddef.h> (7.19), the mbtowc function
         (7.22.7.2), Unicode utilities <uchar.h> (7.28).

### 6.4.5 [String literals]

    1 Syntax
                 string-literal:
                          encoding-prefixopt " s-char-sequenceopt "
                  encoding-prefix:
                         u8
                         u
                         U
                         L
                  s-char-sequence:
                         s-char
                         s-char-sequence s-char
                  s-char:
                            any member of the source character set except
                                         the double-quote ", backslash \, or new-line character
                            escape-sequence
         Constraints

    2    A sequence of adjacent string literal tokens shall not include both a wide string literal and
         a UTF−8 string literal.
         Description

    3    A character string literal is a sequence of zero or more multibyte characters enclosed in
         double-quotes, as in "xyz". A UTF−8 string literal is the same, except prefixed by u8.
         A wide string literal is the same, except prefixed by the letter L, u, or U.

    4    The same considerations apply to each element of the sequence in a string literal as if it
         were in an integer character constant (for a character or UTF−8 string literal) or a wide
         character constant (for a wide string literal), except that the single-quote ' is
         representable either by itself or by the escape sequence \', but the double-quote " shall
        be represented by the escape sequence \".
        Semantics

    5   In translation phase 6, the multibyte character sequences specified by any sequence of
        adjacent character and identically-prefixed string literal tokens are concatenated into a
        single multibyte character sequence. If any of the tokens has an encoding prefix, the
        resulting multibyte character sequence is treated as having the same prefix; otherwise, it
        is treated as a character string literal. Whether differently-prefixed wide string literal
        tokens can be concatenated and, if so, the treatment of the resulting multibyte character
        sequence are implementation-defined.

    6   In translation phase 7, a byte or code of value zero is appended to each multibyte
        character sequence that results from a string literal or literals.[78] The multibyte character
        sequence is then used to initialize an array of static storage duration and length just
        sufficient to contain the sequence. For character string literals, the array elements have
        type char, and are initialized with the individual bytes of the multibyte character
        sequence. For UTF−8 string literals, the array elements have type char, and are
        initialized with the characters of the multibyte character sequence, as encoded in UTF−8.
        For wide string literals prefixed by the letter L, the array elements have type wchar_t
        and are initialized with the sequence of wide characters corresponding to the multibyte
        character sequence, as defined by the mbstowcs function with an implementation-
        defined current locale. For wide string literals prefixed by the letter u or U, the array
        elements have type char16_t or char32_t, respectively, and are initialized with the
        sequence of wide characters corresponding to the multibyte character sequence, as
        defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for
        its type, with an implementation-defined current locale. The value of a string literal
        containing a multibyte character or escape sequence not represented in the execution
        character set is implementation-defined.

    Footnote 78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a
            \0 escape sequence.

    7   It is unspecified whether these arrays are distinct provided their elements have the
        appropriate values. If the program attempts to modify such an array, the behavior is
        undefined.

    8   EXAMPLE 1      This pair of adjacent character string literals
                "\x12" "3"
        produces a single character string literal containing the two characters whose values are '\x12' and '3',
        because escape sequences are converted into single members of the execution character set just prior to
        adjacent string literal concatenation.

    9   EXAMPLE 2      Each of the sequences of adjacent string literal tokens
                 "a" "b" L"c"
                 "a" L"b" "c"
                 L"a" "b" L"c"
                 L"a" L"b" L"c"
        is equivalent to the string literal
                 L"abc"
        Likewise, each of the sequences
                 "a" "b" u"c"
                 "a" u"b" "c"
                 u"a" "b" u"c"
                 u"a" u"b" u"c"
        is equivalent to
                 u"abc"

        Forward references: common definitions <stddef.h> (7.19), the mbstowcs
        function (7.22.8.1), Unicode utilities <uchar.h> (7.28).

### 6.4.6 [Punctuators]

    1 Syntax
                punctuator: one of
                        [ ] ( ) { } . ->
                        ++ -- & * + - ~ !
                        / % << >> < > <= >=                      ==    !=     ^    |   &&   ||
                        ? : ; ...
                        = *= /= %= += -= <<=                     >>=     &=       ^=   |=
                        , # ##
                        <: :> <% %> %: %:%:
        Semantics

    2   A punctuator is a symbol that has independent syntactic and semantic significance.
        Depending on context, it may specify an operation to be performed (which in turn may
        yield a value or a function designator, produce a side effect, or some combination thereof)
        in which case it is known as an operator (other forms of operator also exist in some
        contexts). An operand is an entity on which an operator acts.

    3   In all aspects of the language, the six tokens[79]
                 <:    :>      <%    %>     %:     %:%:
        behave, respectively, the same as the six tokens
                 [     ]       {     }      #      ##
        except for their spelling.[80]
        Forward references: expressions (6.5), declarations (6.7), preprocessing directives
        (6.10), statements (6.8).

    Footnote 79) These tokens are sometimes called ‘‘digraphs’’.

    Footnote 80) Thus [ and <: behave differently when ‘‘stringized’’ (see 6.10.3.2), but can otherwise be freely
            interchanged.

### 6.4.7 [Header names]

    1 Syntax
                header-name:
                        < h-char-sequence >
                        " q-char-sequence "
                 h-char-sequence:
                        h-char
                        h-char-sequence h-char
                 h-char:
                           any member of the source character set except
                                        the new-line character and >
                 q-char-sequence:
                        q-char
                        q-char-sequence q-char
                 q-char:
                           any member of the source character set except
                                        the new-line character and "
        Semantics

    2   The sequences in both forms of header names are mapped in an implementation-defined
        manner to headers or external source file names as specified in 6.10.2.

    3   If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
        the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the
        sequence between the " delimiters, the behavior is undefined.[81] Header name
        preprocessing tokens are recognized only within #include preprocessing directives and
        in implementation-defined locations within #pragma directives.[82]

    Footnote 81) Thus, sequences of characters that resemble escape sequences cause undefined behavior.

    Footnote 82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.

    4   EXAMPLE       The following sequence of characters:
                 0x3<1/a.h>1e2
                 #include <1/a.h>
                 #define const.member@$
        forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
        by a { on the left and a } on the right).
                 {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
                 {#}{include} {<1/a.h>}
                 {#}{define} {const}{.}{member}{@}{$}

        Forward references: source file inclusion (6.10.2).

### 6.4.8 [Preprocessing numbers]

    1 Syntax
                pp-number:
                       digit
                       . digit
                       pp-number digit
                       pp-number identifier-nondigit
                       pp-number e sign
                       pp-number E sign
                       pp-number p sign
                       pp-number P sign
                       pp-number .
        Description

    2   A preprocessing number begins with a digit optionally preceded by a period (.) and may
        be followed by valid identifier characters and the character sequences e+, e-, E+, E-,
        p+, p-, P+, or P-.

    3   Preprocessing number tokens lexically include all floating and integer constant tokens.
        Semantics

    4   A preprocessing number does not have type or a value; it acquires both after a successful
        conversion (as part of translation phase 7) to a floating constant token or an integer
        constant token.

### 6.4.9 [Comments]

    1   Except within a character constant, a string literal, or a comment, the characters /*
        introduce a comment. The contents of such a comment are examined only to identify
        multibyte characters and to find the characters */ that terminate it.[83]

    Footnote 83) Thus, /* ... */ comments do not nest.

    2   Except within a character constant, a string literal, or a comment, the characters //
        introduce a comment that includes all multibyte characters up to, but not including, the
        next new-line character. The contents of such a comment are examined only to identify
        multibyte characters and to find the terminating new-line character.

    3   EXAMPLE
                "a//b"                              // four-character string literal
                #include "//e"                      // undefined behavior
                // */                               // comment, not syntax error
                f = g/**//h;                        // equivalent to f = g / h;
                //\
                i();                                // part of a two-line comment
                /\
                / j();                              // part of a two-line comment
                #define glue(x,y) x##y
                glue(/,/) k();                      // syntax error, not comment
                /*//*/ l();                         // equivalent to l();
                m = n//**/o
                   + p;                             // equivalent to m = n + p;

### 6.5 [Expressions]

    1   An expression is a sequence of operators and operands that specifies computation of a
        value, or that designates an object or a function, or that generates side effects, or that
        performs a combination thereof. The value computations of the operands of an operator
        are sequenced before the value computation of the result of the operator.

    2   If a side effect on a scalar object is unsequenced relative to either a different side effect
        on the same scalar object or a value computation using the value of the same scalar
        object, the behavior is undefined. If there are multiple allowable orderings of the
        subexpressions of an expression, the behavior is undefined if such an unsequenced side
        effect occurs in any of the orderings.[84]

    Footnote 84) This paragraph renders undefined statement expressions such as
                      i = ++i + 1;
                      a[i++] = i;
             while allowing
                      i = i + 1;
                      a[i] = i;

    3   The grouping of operators and operands is indicated by the syntax.[85] Except as specified
        later, side effects and value computations of subexpressions are unsequenced.[86]

    Footnote 85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same
            as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the
            expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
            6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators
            (6.5.3), and an operand contained between any of the following pairs of operators: grouping
            parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and
            the conditional operator ? : (6.5.15).
             Within each major subclause, the operators have the same precedence. Left- or right-associativity is
             indicated in each subclause by the syntax for the expressions discussed therein.

    Footnote 86) In an expression that is evaluated more than once during the execution of a program, unsequenced and
            indeterminately sequenced evaluations of its subexpressions need not be performed consistently in
            different evaluations.

    4   Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,
        collectively described as bitwise operators) are required to have operands that have
        integer type. These operators yield values that depend on the internal representations of
        integers, and have implementation-defined and undefined aspects for signed types.

    5   If an exceptional condition occurs during the evaluation of an expression (that is, if the
        result is not mathematically defined or not in the range of representable values for its
        type), the behavior is undefined.

    6   The effective type of an object for an access to its stored value is the declared type of the
        object, if any.[87] If a value is stored into an object having no declared type through an
        lvalue having a type that is not a character type, then the type of the lvalue becomes the
        effective type of the object for that access and for subsequent accesses that do not modify
        the stored value. If a value is copied into an object having no declared type using
        memcpy or memmove, or is copied as an array of character type, then the effective type
        of the modified object for that access and for subsequent accesses that do not modify the
        value is the effective type of the object from which the value is copied, if it has one. For
        all other accesses to an object having no declared type, the effective type of the object is
        simply the type of the lvalue used for the access.

    Footnote 87) Allocated objects have no declared type.

    7   An object shall have its stored value accessed only by an lvalue expression that has one of
        the following types:[88]
        — a type compatible with the effective type of the object,
        — a qualified version of a type compatible with the effective type of the object,
        — a type that is the signed or unsigned type corresponding to the effective type of the
          object,
        — a type that is the signed or unsigned type corresponding to a qualified version of the
          effective type of the object,
        — an aggregate or union type that includes one of the aforementioned types among its
          members (including, recursively, a member of a subaggregate or contained union), or
        — a character type.

    Footnote 88) The intent of this list is to specify those circumstances in which an object may or may not be aliased.

    8   A floating expression may be contracted, that is, evaluated as though it were a single
        operation, thereby omitting rounding errors implied by the source code and the
        expression evaluation method.[89] The FP_CONTRACT pragma in <math.h> provides a
        way to disallow contracted expressions. Otherwise, whether and how expressions are
        contracted is implementation-defined.[90]
        Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.24.2).

    Footnote 89) The intermediate operations in the contracted expression are evaluated as if to infinite range and
            precision, while the final operation is rounded to the format determined by the expression evaluation
            method. A contracted expression might also omit the raising of floating-point exceptions.

    Footnote 90) This license is specifically intended to allow implementations to exploit fast machine instructions that
            combine multiple C operators. As contractions potentially undermine predictability, and can even
            decrease accuracy for containing expressions, their use needs to be well-defined and clearly
            documented.

### 6.5.1 [Primary expressions]

    1 Syntax
                primary-expression:
                        identifier
                        constant
                        string-literal
                        ( expression )
                        generic-selection
        Semantics

    2   An identifier is a primary expression, provided it has been declared as designating an
        object (in which case it is an lvalue) or a function (in which case it is a function
        designator).[91]

    Footnote 91) Thus, an undeclared identifier is a violation of the syntax.

    3   A constant is a primary expression. Its type depends on its form and value, as detailed in
        6.4.4.

    4   A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.

    5   A parenthesized expression is a primary expression. Its type and value are identical to
        those of the unparenthesized expression. It is an lvalue, a function designator, or a void
        expression if the unparenthesized expression is, respectively, an lvalue, a function
        designator, or a void expression.

    6   A generic selection is a primary expression. Its type and value depend on the selected
        generic association, as detailed in the following subclause.
        Forward references: declarations (6.7).

### 6.5.1.1 [Generic selection]

    1 Syntax
                generic-selection:
                        _Generic ( assignment-expression , generic-assoc-list )
                 generic-assoc-list:
                        generic-association
                        generic-assoc-list , generic-association
                 generic-association:
                        type-name : assignment-expression
                        default : assignment-expression
        Constraints

    2   A generic selection shall have no more than one default generic association. The type
        name in a generic association shall specify a complete object type other than a variably
        modified type. No two generic associations in the same generic selection shall specify
        compatible types. The controlling expression of a generic selection shall have type
        compatible with at most one of the types named in its generic association list. If a
        generic selection has no default generic association, its controlling expression shall
        have type compatible with exactly one of the types named in its generic association list.
        Semantics

    3   The controlling expression of a generic selection is not evaluated. If a generic selection
        has a generic association with a type name that is compatible with the type of the
        controlling expression, then the result expression of the generic selection is the
        expression in that generic association. Otherwise, the result expression of the generic
        selection is the expression in the default generic association. None of the expressions
        from any other generic association of the generic selection is evaluated.

    4   The type and value of a generic selection are identical to those of its result expression. It
        is an lvalue, a function designator, or a void expression if its result expression is,
        respectively, an lvalue, a function designator, or a void expression.

    5   EXAMPLE      The cbrt type-generic macro could be implemented as follows:
                 #define cbrt(X) _Generic((X),                                      \
                                         long double: cbrtl,                        \
                                         default: cbrt,                             \
                                         float: cbrtf                               \
                                         )(X)

### 6.5.2 [Postfix operators]

    1 Syntax
                postfix-expression:
                         primary-expression
                         postfix-expression [ expression ]
                         postfix-expression ( argument-expression-listopt )
                         postfix-expression . identifier
                         postfix-expression -> identifier
                         postfix-expression ++
                         postfix-expression --
                         ( type-name ) { initializer-list }
                         ( type-name ) { initializer-list , }
                 argument-expression-list:
                       assignment-expression
                       argument-expression-list , assignment-expression

### 6.5.2.1 [Array subscripting]

    1 Constraints
       One of the expressions shall have type ‘‘pointer to complete object type’’, the other
        expression shall have integer type, and the result has type ‘‘type’’.
        Semantics

    2   A postfix expression followed by an expression in square brackets [] is a subscripted
        designation of an element of an array object. The definition of the subscript operator []
        is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
        apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the
        initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th
        element of E1 (counting from zero).

    3   Successive subscript operators designate an element of a multidimensional array object.
        If E is an n-dimensional array (n ≥ 2) with dimensions i × j × . . . × k, then E (used as
        other than an lvalue) is converted to a pointer to an (n − 1)-dimensional array with
        dimensions j × . . . × k. If the unary * operator is applied to this pointer explicitly, or
        implicitly as a result of subscripting, the result is the referenced (n − 1)-dimensional
        array, which itself is converted into a pointer if used as other than an lvalue. It follows
        from this that arrays are stored in row-major order (last subscript varies fastest).

    4   EXAMPLE        Consider the array object defined by the declaration
                 int x[3][5];
        Here x is a 3 × 5 array of ints; more precisely, x is an array of three element objects, each of which is an
        array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to
        a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually
        entails multiplying i by the size of the object to which the pointer points, namely an array of five int
        objects. The results are added and indirection is applied to yield an array of five ints. When used in the
        expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]
        yields an int.

        Forward references: additive operators (6.5.6), address and indirection operators
        (6.5.3.2), array declarators (6.7.6.2).

### 6.5.2.2 [Function calls]

    1 Constraints
       The expression that denotes the called function[92] shall have type pointer to function
        returning void or returning a complete object type other than an array type.

    Footnote 92) Most often, this is the result of converting an identifier that is a function designator.

    2   If the expression that denotes the called function has a type that includes a prototype, the
        number of arguments shall agree with the number of parameters. Each argument shall
        have a type such that its value may be assigned to an object with the unqualified version
        of the type of its corresponding parameter.
        Semantics

    3   A postfix expression followed by parentheses () containing a possibly empty, comma-
        separated list of expressions is a function call. The postfix expression denotes the called
        function. The list of expressions specifies the arguments to the function.

    4   An argument may be an expression of any complete object type. In preparing for the call
        to a function, the arguments are evaluated, and each parameter is assigned the value of the
        corresponding argument.[93]

    Footnote 93) A function may change the values of its parameters, but these changes cannot affect the values of the
            arguments. On the other hand, it is possible to pass a pointer to an object, and the function may
            change the value of the object pointed to. A parameter declared to have array or function type is
            adjusted to have a pointer type as described in 6.9.1.

    5   If the expression that denotes the called function has type pointer to function returning an
        object type, the function call expression has the same type as that object type, and has the
        value determined as specified in 6.8.6.4. Otherwise, the function call has type void.

    6   If the expression that denotes the called function has a type that does not include a
        prototype, the integer promotions are performed on each argument, and arguments that
        have type float are promoted to double. These are called the default argument
        promotions. If the number of arguments does not equal the number of parameters, the
        behavior is undefined. If the function is defined with a type that includes a prototype, and
        either the prototype ends with an ellipsis (, ...) or the types of the arguments after
        promotion are not compatible with the types of the parameters, the behavior is undefined.
        If the function is defined with a type that does not include a prototype, and the types of
        the arguments after promotion are not compatible with those of the parameters after
        promotion, the behavior is undefined, except for the following cases:
        — one promoted type is a signed integer type, the other promoted type is the
          corresponding unsigned integer type, and the value is representable in both types;
         — both types are pointers to qualified or unqualified versions of a character type or
           void.

    7    If the expression that denotes the called function has a type that does include a prototype,
         the arguments are implicitly converted, as if by assignment, to the types of the
         corresponding parameters, taking the type of each parameter to be the unqualified version
         of its declared type. The ellipsis notation in a function prototype declarator causes
         argument type conversion to stop after the last declared parameter. The default argument
         promotions are performed on trailing arguments.

    8    No other conversions are performed implicitly; in particular, the number and types of
         arguments are not compared with those of the parameters in a function definition that
         does not include a function prototype declarator.

    9    If the function is defined with a type that is not compatible with the type (of the
         expression) pointed to by the expression that denotes the called function, the behavior is
         undefined.

    10   There is a sequence point after the evaluations of the function designator and the actual
         arguments but before the actual call. Every evaluation in the calling function (including
         other function calls) that is not otherwise specifically sequenced before or after the
         execution of the body of the called function is indeterminately sequenced with respect to
         the execution of the called function.[94]

    Footnote 94) In other words, function executions do not ‘‘interleave’’ with each other.

    11   Recursive function calls shall be permitted, both directly and indirectly through any chain
         of other functions.

    12   EXAMPLE        In the function call
                  (*pf[f1()]) (f2(), f3() + f4())
         the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
         the function pointed to by pf[f1()] is called.

         Forward references: function declarators (including prototypes) (6.7.6.3), function
         definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).

### 6.5.2.3 [Structure and union members]

    1 Constraints
        The first operand of the . operator shall have an atomic, qualified, or unqualified
         structure or union type, and the second operand shall name a member of that type.

    2    The first operand of the -> operator shall have type ‘‘pointer to atomic, qualified, or
         unqualified structure’’ or ‘‘pointer to atomic, qualified, or unqualified union’’, and the
         second operand shall name a member of the type pointed to.
        Semantics

    3   A postfix expression followed by the . operator and an identifier designates a member of
        a structure or union object. The value is that of the named member,[95] and is an lvalue if
        the first expression is an lvalue. If the first expression has qualified type, the result has
        the so-qualified version of the type of the designated member.

    Footnote 95) If the member used to read the contents of a union object is not the same as the member last used to
            store a value in the object, the appropriate part of the object representation of the value is reinterpreted
            as an object representation in the new type as described in 6.2.6 (a process sometimes called ‘‘type
            punning’’). This might be a trap representation.

    4   A postfix expression followed by the -> operator and an identifier designates a member
        of a structure or union object. The value is that of the named member of the object to
        which the first expression points, and is an lvalue.[96] If the first expression is a pointer to
        a qualified type, the result has the so-qualified version of the type of the designated
        member.

    Footnote 96) If &E is a valid pointer expression (where & is the ‘‘address-of ’’ operator, which generates a pointer to
            its operand), the expression (&E)->MOS is the same as E.MOS.

    5   Accessing a member of an atomic structure or union object results in undefined
        behavior.[97]

    Footnote 97) For example, a data race would occur if access to the entire structure or union in one thread conflicts
            with access to a member from another thread, where at least one access is a modification. Members
            can be safely accessed using a non-atomic object which is assigned to or from the atomic object.

    6   One special guarantee is made in order to simplify the use of unions: if a union contains
        several structures that share a common initial sequence (see below), and if the union
        object currently contains one of these structures, it is permitted to inspect the common
        initial part of any of them anywhere that a declaration of the completed type of the union
        is visible. Two structures share a common initial sequence if corresponding members
        have compatible types (and, for bit-fields, the same widths) for a sequence of one or more
        initial members.

    7   EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or
        union, f().x is a valid postfix expression but is not an lvalue.

    8   EXAMPLE 2       In:
                 struct s { int i; const int ci; };
                 struct s s;
                 const struct s cs;
                 volatile struct s vs;
        the various members have the types:
                 s.i        int
                 s.ci       const int
                 cs.i       const int
                 cs.ci      const int
                 vs.i       volatile int
                 vs.ci      volatile const int

    9   EXAMPLE 3       The following is a valid fragment:
                 union {
                         struct {
                               int      alltypes;
                         } n;
                         struct {
                               int      type;
                               int      intnode;
                         } ni;
                         struct {
                               int      type;
                               double doublenode;
                         } nf;
                 } u;
                 u.nf.type = 1;
                 u.nf.doublenode = 3.14;
                 /* ... */
                 if (u.n.alltypes == 1)
                         if (sin(u.nf.doublenode) == 0.0)
                               /* ... */
        The following is not a valid fragment (because the union type is not visible within function f):
                 struct t1 { int m; };
                 struct t2 { int m; };
                 int f(struct t1 *p1, struct t2 *p2)
                 {
                       if (p1->m < 0)
                               p2->m = -p2->m;
                       return p1->m;
                 }
                 int g()
                 {
                       union {
                               struct t1 s1;
                               struct t2 s2;
                       } u;
                       /* ... */
                       return f(&u.s1, &u.s2);
                 }

        Forward references: address and indirection operators (6.5.3.2), structure and union
        specifiers (6.7.2.1).

### 6.5.2.4 [Postfix increment and decrement operators]

    1 Constraints
       The operand of the postfix increment or decrement operator shall have atomic, qualified,
        or unqualified real or pointer type, and shall be a modifiable lvalue.
        Semantics

    2   The result of the postfix ++ operator is the value of the operand. As a side effect, the
        value of the operand object is incremented (that is, the value 1 of the appropriate type is
        added to it). See the discussions of additive operators and compound assignment for
        information on constraints, types, and conversions and the effects of operations on
        pointers. The value computation of the result is sequenced before the side effect of
        updating the stored value of the operand. With respect to an indeterminately-sequenced
        function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object
        with atomic type is a read-modify-write operation with memory_order_seq_cst
        memory order semantics.[98]

    Footnote 98) Where a pointer to an atomic object can be formed and E has integer type, E++ is equivalent to the
            following code sequence where T is the type of E:
                      T *addr = &E;
                      T old = *addr;
                      T new;
                      do {
                             new = old + 1;
                      } while (!atomic_compare_exchange_strong(addr, &old, new));
             with old being the result of the operation.
             Special care must be taken if E has floating type; see 6.5.16.2.

    3   The postfix -- operator is analogous to the postfix ++ operator, except that the value of
        the operand is decremented (that is, the value 1 of the appropriate type is subtracted from
        it).
        Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).

### 6.5.2.5 [Compound literals]

    1 Constraints
       The type name shall specify a complete object type or an array of unknown size, but not a
        variable length array type.

    2   All the constraints for initializer lists in 6.7.9 also apply to compound literals.
        Semantics

    3   A postfix expression that consists of a parenthesized type name followed by a brace-
        enclosed list of initializers is a compound literal. It provides an unnamed object whose
         value is given by the initializer list.[99]

    Footnote 99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
             or void only, and the result of a cast expression is not an lvalue.

    4    If the type name specifies an array of unknown size, the size is determined by the
         initializer list as specified in 6.7.9, and the type of the compound literal is that of the
         completed array type. Otherwise (when the type name specifies an object type), the type
         of the compound literal is that specified by the type name. In either case, the result is an
         lvalue.

    5    The value of the compound literal is that of an unnamed object initialized by the
         initializer list. If the compound literal occurs outside the body of a function, the object
         has static storage duration; otherwise, it has automatic storage duration associated with
         the enclosing block.

    6    All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.[100]

    Footnote 100) For example, subobjects without explicit initializers are initialized to zero.

    7    String literals, and compound literals with const-qualified types, need not designate
         distinct objects.[101]

    Footnote 101) This allows implementations to share storage for string literals and constant compound literals with
              the same or overlapping representations.

    8    EXAMPLE 1       The file scope definition
                  int *p = (int []){2, 4};
         initializes p to point to the first element of an array of two ints, the first having the value two and the
         second, four. The expressions in this compound literal are required to be constant. The unnamed object
         has static storage duration.

    9    EXAMPLE 2       In contrast, in
                  void f(void)
                  {
                        int *p;
                        /*...*/
                        p = (int [2]){*p};
                        /*...*/
                  }
         p is assigned the address of the first element of an array of two ints, the first having the value previously
         pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
         unnamed object has automatic storage duration.

    10   EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
         created using compound literals can be passed to functions without depending on member order:
                  drawline((struct point){.x=1, .y=1},
                        (struct point){.x=3, .y=4});
         Or, if drawline instead expected pointers to struct point:
                  drawline(&(struct point){.x=1, .y=1},
                        &(struct point){.x=3, .y=4});

    11   EXAMPLE 4        A read-only compound literal can be specified through constructions like:
                  (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}

    12   EXAMPLE 5        The following three expressions have different meanings:
                  "/tmp/fileXXXXXX"
                  (char []){"/tmp/fileXXXXXX"}
                  (const char []){"/tmp/fileXXXXXX"}
         The first always has static storage duration and has type array of char, but need not be modifiable; the last
         two have automatic storage duration when they occur within the body of a function, and the first of these
         two is modifiable.

    13   EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory
         and can even be shared. For example,
                  (const char []){"abc"} == "abc"
         might yield 1 if the literals’ storage is shared.

    14   EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
         linked object. For example, there is no way to write a self-referential compound literal that could be used
         as the function argument in place of the named object endless_zeros below:
                  struct int_list { int car; struct int_list *cdr; };
                  struct int_list endless_zeros = {0, &endless_zeros};
                  eval(endless_zeros);

    15   EXAMPLE 8        Each compound literal creates only a single object in a given scope:
                  struct s { int i; };
                  int f (void)
                  {
                        struct s *p = 0, *q;
                        int j = 0;
                  again:
                            q = p, p = &((struct s){ j++ });
                            if (j < 2) goto again;
                            return p == q && q->i == 1;
                  }
         The function f() always returns the value 1.

    16   Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the
         lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
         have an indeterminate value, which would result in undefined behavior.

         Forward references: type names (6.7.7), initialization (6.7.9).

### 6.5.3 [Unary operators]

    1 Syntax
                unary-expression:
                        postfix-expression
                        ++ unary-expression
                        -- unary-expression
                        unary-operator cast-expression
                        sizeof unary-expression
                        sizeof ( type-name )
                        _Alignof ( type-name )
                 unary-operator: one of
                        & * + - ~             !

### 6.5.3.1 [Prefix increment and decrement operators]

    1 Constraints
       The operand of the prefix increment or decrement operator shall have atomic, qualified,
        or unqualified real or pointer type, and shall be a modifiable lvalue.
        Semantics

    2   The value of the operand of the prefix ++ operator is incremented. The result is the new
        value of the operand after incrementation. The expression ++E is equivalent to (E+=1).
        See the discussions of additive operators and compound assignment for information on
        constraints, types, side effects, and conversions and the effects of operations on pointers.

    3   The prefix -- operator is analogous to the prefix ++ operator, except that the value of the
        operand is decremented.
        Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).

### 6.5.3.2 [Address and indirection operators]

    1 Constraints
       The operand of the unary & operator shall be either a function designator, the result of a
        [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
        not declared with the register storage-class specifier.

    2   The operand of the unary * operator shall have pointer type.
        Semantics

    3   The unary & operator yields the address of its operand. If the operand has type ‘‘type’’,
        the result has type ‘‘pointer to type’’. If the operand is the result of a unary * operator,
        neither that operator nor the & operator is evaluated and the result is as if both were
        omitted, except that the constraints on the operators still apply and the result is not an
        lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor
        the unary * that is implied by the [] is evaluated and the result is as if the & operator
        were removed and the [] operator were changed to a + operator. Otherwise, the result is
        a pointer to the object or function designated by its operand.

    4   The unary * operator denotes indirection. If the operand points to a function, the result is
        a function designator; if it points to an object, the result is an lvalue designating the
        object. If the operand has type ‘‘pointer to type’’, the result has type ‘‘type’’. If an
        invalid value has been assigned to the pointer, the behavior of the unary * operator is
        undefined.[102]
        Forward references: storage-class specifiers (6.7.1), structure and union specifiers
        (6.7.2.1).

    Footnote 102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is
             always true that if E is a function designator or an lvalue that is a valid operand of the unary &
             operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of
             an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
             Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an
             address inappropriately aligned for the type of object pointed to, and the address of an object after the
             end of its lifetime.

### 6.5.3.3 [Unary arithmetic operators]

    1 Constraints
       The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
        integer type; of the ! operator, scalar type.
        Semantics

    2   The result of the unary + operator is the value of its (promoted) operand. The integer
        promotions are performed on the operand, and the result has the promoted type.

    3   The result of the unary - operator is the negative of its (promoted) operand. The integer
        promotions are performed on the operand, and the result has the promoted type.

    4   The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,
        each bit in the result is set if and only if the corresponding bit in the converted operand is
        not set). The integer promotions are performed on the operand, and the result has the
        promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
        to the maximum value representable in that type minus E.

    5   The result of the logical negation operator ! is 0 if the value of its operand compares
        unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
        The expression !E is equivalent to (0==E).

### 6.5.3.4 [The sizeof and _Alignof operators]

    1 Constraints
       The sizeof operator shall not be applied to an expression that has function type or an
        incomplete type, to the parenthesized name of such a type, or to an expression that
        designates a bit-field member. The _Alignof operator shall not be applied to a
        function type or an incomplete type.
        Semantics

    2   The sizeof operator yields the size (in bytes) of its operand, which may be an
        expression or the parenthesized name of a type. The size is determined from the type of
        the operand. The result is an integer. If the type of the operand is a variable length array
        type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
        integer constant.

    3   The _Alignof operator yields the alignment requirement of its operand type. The
        operand is not evaluated and the result is an integer constant. When applied to an array
        type, the result is the alignment requirement of the element type.

    4   When sizeof is applied to an operand that has type char, unsigned char, or
        signed char, (or a qualified version thereof) the result is 1. When applied to an
        operand that has array type, the result is the total number of bytes in the array.[103] When
        applied to an operand that has structure or union type, the result is the total number of
        bytes in such an object, including internal and trailing padding.

    Footnote 103) When applied to a parameter declared to have array or function type, the sizeof operator yields the
             size of the adjusted (pointer) type (see 6.9.1).

    5   The value of the result of both operators is implementation-defined, and its type (an
        unsigned integer type) is size_t, defined in <stddef.h> (and other headers).

    6   EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
        allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to
        allocate and return a pointer to void. For example:
                extern void *alloc(size_t);
                double *dp = alloc(sizeof *dp);
        The implementation of the alloc function should ensure that its return value is aligned suitably for
        conversion to a pointer to double.

    7   EXAMPLE 2      Another use of the sizeof operator is to compute the number of elements in an array:
                sizeof array / sizeof array[0]

    8   EXAMPLE 3      In this example, the size of a variable length array is computed and returned from a
        function:
                #include <stddef.h>
                 size_t fsize3(int n)
                 {
                       char b[n+3];                   // variable length array
                       return sizeof b;               // execution time sizeof
                 }
                 int main()
                 {
                       size_t size;
                       size = fsize3(10); // fsize3 returns 13
                       return 0;
                 }

        Forward references: common definitions <stddef.h> (7.19), declarations (6.7),
        structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2).

### 6.5.4 [Cast operators]

    1 Syntax
                cast-expression:
                        unary-expression
                        ( type-name ) cast-expression
        Constraints

    2   Unless the type name specifies a void type, the type name shall specify atomic, qualified,
        or unqualified scalar type, and the operand shall have scalar type.

    3   Conversions that involve pointers, other than where permitted by the constraints of
        6.5.16.1, shall be specified by means of an explicit cast.

    4   A pointer type shall not be converted to any floating type. A floating type shall not be
        converted to any pointer type.
        Semantics

    5   Preceding an expression by a parenthesized type name converts the value of the
        expression to the named type. This construction is called a cast.[104] A cast that specifies
        no conversion has no effect on the type or value of an expression.

    Footnote 104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the
             unqualified version of the type.

    6   If the value of the expression is represented with greater range or precision than required
        by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the
        type of the expression is the same as the named type and removes any extra range and
        precision.
        Forward references: equality operators (6.5.9), function declarators (including
        prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).

### 6.5.5 [Multiplicative operators]

    1 Syntax
                multiplicative-expression:
                         cast-expression
                         multiplicative-expression * cast-expression
                         multiplicative-expression / cast-expression
                         multiplicative-expression % cast-expression
        Constraints

    2   Each of the operands shall have arithmetic type. The operands of the % operator shall
        have integer type.
        Semantics

    3   The usual arithmetic conversions are performed on the operands.

    4   The result of the binary * operator is the product of the operands.

    5   The result of the / operator is the quotient from the division of the first operand by the
        second; the result of the % operator is the remainder. In both operations, if the value of
        the second operand is zero, the behavior is undefined.

    6   When integers are divided, the result of the / operator is the algebraic quotient with any
        fractional part discarded.[105] If the quotient a/b is representable, the expression
        (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is
        undefined.

    Footnote 105) This is often called ‘‘truncation toward zero’’.

### 6.5.6 [Additive operators]

    1 Syntax
                additive-expression:
                        multiplicative-expression
                        additive-expression + multiplicative-expression
                        additive-expression - multiplicative-expression
        Constraints

    2   For addition, either both operands shall have arithmetic type, or one operand shall be a
        pointer to a complete object type and the other shall have integer type. (Incrementing is
        equivalent to adding 1.)

    3   For subtraction, one of the following shall hold:
        — both operands have arithmetic type;
        — both operands are pointers to qualified or unqualified versions of compatible complete
          object types; or
        — the left operand is a pointer to a complete object type and the right operand has
          integer type.
        (Decrementing is equivalent to subtracting 1.)
        Semantics

    4   If both operands have arithmetic type, the usual arithmetic conversions are performed on
        them.

    5   The result of the binary + operator is the sum of the operands.

    6   The result of the binary - operator is the difference resulting from the subtraction of the
        second operand from the first.

    7   For the purposes of these operators, a pointer to an object that is not an element of an
        array behaves the same as a pointer to the first element of an array of length one with the
        type of the object as its element type.

    8   When an expression that has integer type is added to or subtracted from a pointer, the
        result has the type of the pointer operand. If the pointer operand points to an element of
        an array object, and the array is large enough, the result points to an element offset from
        the original element such that the difference of the subscripts of the resulting and original
        array elements equals the integer expression. In other words, if the expression P points to
        the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
        (P)-N (where N has the value n) point to, respectively, the i+n-th and i−n-th elements of
        the array object, provided they exist. Moreover, if the expression P points to the last
        element of an array object, the expression (P)+1 points one past the last element of the
        array object, and if the expression Q points one past the last element of an array object,
        the expression (Q)-1 points to the last element of the array object. If both the pointer
        operand and the result point to elements of the same array object, or one past the last
        element of the array object, the evaluation shall not produce an overflow; otherwise, the
        behavior is undefined. If the result points one past the last element of the array object, it
        shall not be used as the operand of a unary * operator that is evaluated.

    9   When two pointers are subtracted, both shall point to elements of the same array object,
        or one past the last element of the array object; the result is the difference of the
        subscripts of the two array elements. The size of the result is implementation-defined,
        and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header.
        If the result is not representable in an object of that type, the behavior is undefined. In
        other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of
        an array object, the expression (P)-(Q) has the value i−j provided the value fits in an
         object of type ptrdiff_t. Moreover, if the expression P points either to an element of
         an array object or one past the last element of an array object, and the expression Q points
         to the last element of the same array object, the expression ((Q)+1)-(P) has the same
         value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the
         expression P points one past the last element of the array object, even though the
         expression (Q)+1 does not point to an element of the array object.[106]

    Footnote 106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
              this scheme the integer expression added to or subtracted from the converted pointer is first multiplied
              by the size of the object originally pointed to, and the resulting pointer is converted back to the
              original type. For pointer subtraction, the result of the difference between the character pointers is
              similarly divided by the size of the object originally pointed to.
              When viewed in this way, an implementation need only provide one extra byte (which may overlap
              another object in the program) just after the end of the object in order to satisfy the ‘‘one past the last
              element’’ requirements.

    10   EXAMPLE        Pointer arithmetic is well defined with pointers to variable length array types.
                  {
                           int n = 4, m = 3;
                           int a[n][m];
                           int (*p)[m] = a; // p == &a[0]
                           p += 1;           // p == &a[1]
                           (*p)[2] = 99;     // a[1][2] == 99
                           n = p - a;        // n == 1
                  }

    11   If array a in the above example were declared to be an array of known constant size, and pointer p were
         declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
         the same.

         Forward references: array declarators (6.7.6.2), common definitions <stddef.h>
         (7.19).

### 6.5.7 [Bitwise shift operators]

    1 Syntax
                 shift-expression:
                          additive-expression
                          shift-expression << additive-expression
                          shift-expression >> additive-expression
         Constraints

    2    Each of the operands shall have integer type.
         Semantics

    3    The integer promotions are performed on each of the operands. The type of the result is
         that of the promoted left operand. If the value of the right operand is negative or is
        greater than or equal to the width of the promoted left operand, the behavior is undefined.

    4   The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with
        zeros. If E1 has an unsigned type, the value of the result is E1 × 2E2 , reduced modulo
        one more than the maximum value representable in the result type. If E1 has a signed
        type and nonnegative value, and E1 × 2E2 is representable in the result type, then that is
        the resulting value; otherwise, the behavior is undefined.

    5   The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type
        or if E1 has a signed type and a nonnegative value, the value of the result is the integral
        part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
        resulting value is implementation-defined.

### 6.5.8 [Relational operators]

    1 Syntax
                relational-expression:
                         shift-expression
                         relational-expression < shift-expression
                         relational-expression > shift-expression
                         relational-expression <= shift-expression
                         relational-expression >= shift-expression
        Constraints

    2   One of the following shall hold:
        — both operands have real type; or
        — both operands are pointers to qualified or unqualified versions of compatible object
          types.
        Semantics

    3   If both of the operands have arithmetic type, the usual arithmetic conversions are
        performed.

    4   For the purposes of these operators, a pointer to an object that is not an element of an
        array behaves the same as a pointer to the first element of an array of length one with the
        type of the object as its element type.

    5   When two pointers are compared, the result depends on the relative locations in the
        address space of the objects pointed to. If two pointers to object types both point to the
        same object, or both point one past the last element of the same array object, they
        compare equal. If the objects pointed to are members of the same aggregate object,
        pointers to structure members declared later compare greater than pointers to members
        declared earlier in the structure, and pointers to array elements with larger subscript
        values compare greater than pointers to elements of the same array with lower subscript
        values. All pointers to members of the same union object compare equal. If the
        expression P points to an element of an array object and the expression Q points to the
        last element of the same array object, the pointer expression Q+1 compares greater than
        P. In all other cases, the behavior is undefined.

    6   Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=
        (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is
        false.[107] The result has type int.

    Footnote 107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it
             means (a<b)<c; in other words, ‘‘if a is less than b, compare 1 to c; otherwise, compare 0 to c’’.

### 6.5.9 [Equality operators]

    1 Syntax
                equality-expression:
                        relational-expression
                        equality-expression == relational-expression
                        equality-expression != relational-expression
        Constraints

    2   One of the following shall hold:
        — both operands have arithmetic type;
        — both operands are pointers to qualified or unqualified versions of compatible types;
        — one operand is a pointer to an object type and the other is a pointer to a qualified or
          unqualified version of void; or
        — one operand is a pointer and the other is a null pointer constant.
        Semantics

    3   The == (equal to) and != (not equal to) operators are analogous to the relational
        operators except for their lower precedence.[108] Each of the operators yields 1 if the
        specified relation is true and 0 if it is false. The result has type int. For any pair of
        operands, exactly one of the relations is true.

    Footnote 108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.

    4   If both of the operands have arithmetic type, the usual arithmetic conversions are
        performed. Values of complex types are equal if and only if both their real parts are equal
        and also their imaginary parts are equal. Any two values of arithmetic types from
        different type domains are equal if and only if the results of their conversions to the
        (complex) result type determined by the usual arithmetic conversions are equal.

    5   Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a
        null pointer constant, the null pointer constant is converted to the type of the pointer. If
        one operand is a pointer to an object type and the other is a pointer to a qualified or
        unqualified version of void, the former is converted to the type of the latter.

    6   Two pointers compare equal if and only if both are null pointers, both are pointers to the
        same object (including a pointer to an object and a subobject at its beginning) or function,
        both are pointers to one past the last element of the same array object, or one is a pointer
        to one past the end of one array object and the other is a pointer to the start of a different
        array object that happens to immediately follow the first array object in the address
        space.[109]

    Footnote 109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or
             adjacent members of a structure with no padding between them, or because the implementation chose
             to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses
             outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined
             behavior.

    7   For the purposes of these operators, a pointer to an object that is not an element of an
        array behaves the same as a pointer to the first element of an array of length one with the
        type of the object as its element type.

### 6.5.10 [Bitwise AND operator]

    1 Syntax
                AND-expression:
                       equality-expression
                       AND-expression & equality-expression
        Constraints

    2   Each of the operands shall have integer type.
        Semantics

    3   The usual arithmetic conversions are performed on the operands.

    4   The result of the binary & operator is the bitwise AND of the operands (that is, each bit in
        the result is set if and only if each of the corresponding bits in the converted operands is
        set).

### 6.5.11 [Bitwise exclusive OR operator]

    1 Syntax
                exclusive-OR-expression:
                         AND-expression
                         exclusive-OR-expression ^ AND-expression
        Constraints

    2   Each of the operands shall have integer type.
        Semantics

    3   The usual arithmetic conversions are performed on the operands.

    4   The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit
        in the result is set if and only if exactly one of the corresponding bits in the converted
        operands is set).

### 6.5.12 [Bitwise inclusive OR operator]

    1 Syntax
                inclusive-OR-expression:
                         exclusive-OR-expression
                         inclusive-OR-expression | exclusive-OR-expression
        Constraints

    2   Each of the operands shall have integer type.
        Semantics

    3   The usual arithmetic conversions are performed on the operands.

    4   The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in
        the result is set if and only if at least one of the corresponding bits in the converted
        operands is set).

### 6.5.13 [Logical AND operator]

    1 Syntax
                logical-AND-expression:
                         inclusive-OR-expression
                         logical-AND-expression && inclusive-OR-expression
        Constraints

    2   Each of the operands shall have scalar type.
        Semantics

    3   The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it
        yields 0. The result has type int.

    4   Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation;
        if the second operand is evaluated, there is a sequence point between the evaluations of
        the first and second operands. If the first operand compares equal to 0, the second
        operand is not evaluated.

### 6.5.14 [Logical OR operator]

    1 Syntax
                logical-OR-expression:
                         logical-AND-expression
                         logical-OR-expression || logical-AND-expression
        Constraints

    2   Each of the operands shall have scalar type.
        Semantics

    3   The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it
        yields 0. The result has type int.

    4   Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the
        second operand is evaluated, there is a sequence point between the evaluations of the first
        and second operands. If the first operand compares unequal to 0, the second operand is
        not evaluated.

### 6.5.15 [Conditional operator]

    1 Syntax
                conditional-expression:
                        logical-OR-expression
                        logical-OR-expression ? expression : conditional-expression
        Constraints

    2   The first operand shall have scalar type.

    3   One of the following shall hold for the second and third operands:
        — both operands have arithmetic type;
        — both operands have the same structure or union type;
        — both operands have void type;
        — both operands are pointers to qualified or unqualified versions of compatible types;
        — one operand is a pointer and the other is a null pointer constant; or
        — one operand is a pointer to an object type and the other is a pointer to a qualified or
          unqualified version of void.
        Semantics

    4   The first operand is evaluated; there is a sequence point between its evaluation and the
        evaluation of the second or third operand (whichever is evaluated). The second operand
        is evaluated only if the first compares unequal to 0; the third operand is evaluated only if
        the first compares equal to 0; the result is the value of the second or third operand
        (whichever is evaluated), converted to the type described below.[110]

    Footnote 110) A conditional expression does not yield an lvalue.

    5   If both the second and third operands have arithmetic type, the result type that would be
        determined by the usual arithmetic conversions, were they applied to those two operands,
        is the type of the result. If both the operands have structure or union type, the result has
        that type. If both operands have void type, the result has void type.

    6   If both the second and third operands are pointers or one is a null pointer constant and the
        other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers
        of the types referenced by both operands. Furthermore, if both operands are pointers to
        compatible types or to differently qualified versions of compatible types, the result type is
        a pointer to an appropriately qualified version of the composite type; if one operand is a
        null pointer constant, the result has the type of the other operand; otherwise, one operand
        is a pointer to void or a qualified version of void, in which case the result type is a
        pointer to an appropriately qualified version of void.

    7   EXAMPLE The common type that results when the second and third operands are pointers is determined
        in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two
        pointers have compatible types.

    8   Given the declarations
                 const void *c_vp;
                 void *vp;
                 const int *c_ip;
                 volatile int *v_ip;
                 int *ip;
                 const char *c_cp;
        the third column in the following table is the common type that is the result of a conditional expression in
        which the first two columns are the second and third operands (in either order):
                 c_vp     c_ip      const void *
                 v_ip     0         volatile int *
                 c_ip     v_ip      const volatile int *
                 vp       c_cp      const void *
                 ip       c_ip      const int *
                 vp       ip        void *

### 6.5.16 [Assignment operators]

    1 Syntax
                assignment-expression:
                        conditional-expression
                        unary-expression assignment-operator assignment-expression
                 assignment-operator: one of
                        = *= /= %= +=                       -=     <<=      >>=      &=     ^=     |=
        Constraints

    2   An assignment operator shall have a modifiable lvalue as its left operand.
        Semantics

    3   An assignment operator stores a value in the object designated by the left operand. An
        assignment expression has the value of the left operand after the assignment,[111] but is not
        an lvalue. The type of an assignment expression is the type the left operand would have
        after lvalue conversion. The side effect of updating the stored value of the left operand is
        sequenced after the value computations of the left and right operands. The evaluations of
        the operands are unsequenced.

    Footnote 111) The implementation is permitted to read the object to determine the value but is not required to, even
             when the object has volatile-qualified type.

### 6.5.16.1 [Simple assignment]

    1 Constraints
       One of the following shall hold:[112]
        — the left operand has atomic, qualified, or unqualified arithmetic type, and the right has
          arithmetic type;
        — the left operand has an atomic, qualified, or unqualified version of a structure or union
          type compatible with the type of the right;
        — the left operand has atomic, qualified, or unqualified pointer type, and (considering
          the type the left operand would have after lvalue conversion) both operands are
          pointers to qualified or unqualified versions of compatible types, and the type pointed
          to by the left has all the qualifiers of the type pointed to by the right;
        — the left operand has atomic, qualified, or unqualified pointer type, and (considering
          the type the left operand would have after lvalue conversion) one operand is a pointer
          to an object type, and the other is a pointer to a qualified or unqualified version of
          void, and the type pointed to by the left has all the qualifiers of the type pointed to
          by the right;
        — the left operand is an atomic, qualified, or unqualified pointer, and the right is a null
          pointer constant; or
        — the left operand has type atomic, qualified, or unqualified _Bool, and the right is a
          pointer.
        Semantics

    Footnote 112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion
             (specified in 6.3.2.1) that changes lvalues to ‘‘the value of the expression’’ and thus removes any type
             qualifiers that were applied to the type category of the expression (for example, it removes const but
             not volatile from the type int volatile * const).

    2   In simple assignment (=), the value of the right operand is converted to the type of the
        assignment expression and replaces the value stored in the object designated by the left
        operand.

    3   If the value being stored in an object is read from another object that overlaps in any way
        the storage of the first object, then the overlap shall be exact and the two objects shall
        have qualified or unqualified versions of a compatible type; otherwise, the behavior is
        undefined.

    4   EXAMPLE 1       In the program fragment
                int f(void);
                char c;
                /* ... */
                if ((c = f()) == -1)
                        /* ... */
        the int value returned by the function may be truncated when stored in the char, and then converted back
        to int width prior to the comparison. In an implementation in which ‘‘plain’’ char has the same range of
        values as unsigned char (and char is narrower than int), the result of the conversion cannot be
        negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
        variable c should be declared as int.

    5   EXAMPLE 2       In the fragment:
                char c;
                int i;
                long l;
                l = (c = i);
        the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
        of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
        that is, long int type.

    6   EXAMPLE 3       Consider the fragment:
                const char **cpp;
                char *p;
                const char c = 'A';
                cpp = &p;                  // constraint violation
                *cpp = &c;                 // valid
                *p = 0;                    // valid
        The first assignment is unsafe because it would allow the following valid code to attempt to change the
        value of the const object c.

### 6.5.16.2 [Compound assignment]

    1 Constraints
       For the operators += and -= only, either the left operand shall be an atomic, qualified, or
        unqualified pointer to a complete object type, and the right shall have integer type; or the
        left operand shall have atomic, qualified, or unqualified arithmetic type, and the right
        shall have arithmetic type.

    2   For the other operators, the left operand shall have atomic, qualified, or unqualified
        arithmetic type, and (considering the type the left operand would have after lvalue
        conversion) each operand shall have arithmetic type consistent with those allowed by the
        corresponding binary operator.
        Semantics

    3   A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
        expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
        respect to an indeterminately-sequenced function call, the operation of a compound
    assignment is a single evaluation. If E1 has an atomic type, compound assignment is a
    read-modify-write operation with memory_order_seq_cst memory order
    semantics.[113]

    Footnote 113) Where a pointer to an atomic object can be formed and E1 and E2 have integer type, this is equivalent
             to the following code sequence where T1 is the type of E1 and T2 is the type of E2:
                  T1 *addr = &E1;
                  T2 val = (E2);
                  T1 old = *addr;
                  T1 new;
                  do {
                        new = old op val;
                  } while (!atomic_compare_exchange_strong(addr, &old, new));
         with new being the result of the operation.
         If E1 or E2 has floating type, then exceptional conditions or floating-point exceptions encountered
         during discarded evaluations of new should also be discarded in order to satisfy the equivalence of E1
         op = E2 and E1 = E1 op (E2). For example, if annex F is in effect, the floating types involved have
         IEC 60559 formats, and FLT_EVAL_METHOD is 0, the equivalent code would be:
                  #include <fenv.h>
                  #pragma STDC FENV_ACCESS ON
                  /* ... */
                          fenv_t fenv;
                          T1 *addr = &E1;
                          T2 val = E2;
                          T1 old = *addr;
                          T1 new;
                          feholdexcept(&fenv);
                          for (;;) {
                                new = old op val;
                                if (atomic_compare_exchange_strong(addr, &old, new))
                                            break;
                                feclearexcept(FE_ALL_EXCEPT);
                          }
                          feupdateenv(&fenv);
         If FLT_EVAL_METHOD is not 0, then T2 must be a type with the range and precision to which E2 is
         evaluated in order to satisfy the equivalence.

### 6.5.17 [Comma operator]

    1 Syntax
                expression:
                        assignment-expression
                        expression , assignment-expression
        Semantics

    2   The left operand of a comma operator is evaluated as a void expression; there is a
        sequence point between its evaluation and that of the right operand. Then the right
        operand is evaluated; the result has its type and value.[114]

    Footnote 114) A comma operator does not yield an lvalue.

    3   EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
        appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
        of initializers). On the other hand, it can be used within a parenthesized expression or within the second
        expression of a conditional operator in such contexts. In the function call
                 f(a, (t=3, t+2), c)
        the function has three arguments, the second of which has the value 5.

        Forward references: initialization (6.7.9).

### 6.6 [Constant expressions]

    1 Syntax
                constant-expression:
                        conditional-expression
        Description

    2   A constant expression can be evaluated during translation rather than runtime, and
        accordingly may be used in any place that a constant may be.
        Constraints

    3   Constant expressions shall not contain assignment, increment, decrement, function-call,
        or comma operators, except when they are contained within a subexpression that is not
        evaluated.[115]

    Footnote 115) The operand of a sizeof or _Alignof operator is usually not evaluated (6.5.3.4).

    4   Each constant expression shall evaluate to a constant that is in the range of representable
        values for its type.
        Semantics

    5   An expression that evaluates to a constant is required in several contexts. If a floating
        expression is evaluated in the translation environment, the arithmetic range and precision
        shall be at least as great as if the expression were being evaluated in the execution
        environment.[116]

    Footnote 116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
             the translation environment.

    6   An integer constant expression[117] shall have integer type and shall only have operands
        that are integer constants, enumeration constants, character constants, sizeof
        expressions whose results are integer constants, _Alignof expressions, and floating
        constants that are the immediate operands of casts. Cast operators in an integer constant
        expression shall only convert arithmetic types to integer types, except as part of an
        operand to the sizeof or _Alignof operator.

    Footnote 117) An integer constant expression is required in a number of contexts such as the size of a bit-field
             member of a structure, the value of an enumeration constant, and the size of a non-variable length
             array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
             preprocessing directives are discussed in 6.10.1.

    7   More latitude is permitted for constant expressions in initializers. Such a constant
        expression shall be, or evaluate to, one of the following:
        — an arithmetic constant expression,
         — a null pointer constant,
         — an address constant, or
         — an address constant for a complete object type plus or minus an integer constant
           expression.

    8    An arithmetic constant expression shall have arithmetic type and shall only have
         operands that are integer constants, floating constants, enumeration constants, character
         constants, sizeof expressions whose results are integer constants, and _Alignof
         expressions. Cast operators in an arithmetic constant expression shall only convert
         arithmetic types to arithmetic types, except as part of an operand to a sizeof or
         _Alignof operator.

    9    An address constant is a null pointer, a pointer to an lvalue designating an object of static
         storage duration, or a pointer to a function designator; it shall be created explicitly using
         the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
         an expression of array or function type. The array-subscript [] and member-access .
         and -> operators, the address & and indirection * unary operators, and pointer casts may
         be used in the creation of an address constant, but the value of an object shall not be
         accessed by use of these operators.

    10   An implementation may accept other forms of constant expressions.

    11   The semantic rules for the evaluation of a constant expression are the same as for
         nonconstant expressions.[118]
         Forward references: array declarators (6.7.6.2), initialization (6.7.9).

    Footnote 118) Thus, in the following initialization,
                       static int i = 2 || 1 / 0;
              the expression is a valid integer constant expression with value one.

### 6.7 [Declarations]

    1 Syntax
                declaration:
                        declaration-specifiers init-declarator-listopt ;
                        static_assert-declaration
                 declaration-specifiers:
                        storage-class-specifier declaration-specifiersopt
                        type-specifier declaration-specifiersopt
                        type-qualifier declaration-specifiersopt
                        function-specifier declaration-specifiersopt
                        alignment-specifier declaration-specifiersopt
                 init-declarator-list:
                         init-declarator
                         init-declarator-list , init-declarator
                 init-declarator:
                         declarator
                         declarator = initializer
        Constraints

    2   A declaration other than a static_assert declaration shall declare at least a declarator
        (other than the parameters of a function or the members of a structure or union), a tag, or
        the members of an enumeration.

    3   If an identifier has no linkage, there shall be no more than one declaration of the identifier
        (in a declarator or type specifier) with the same scope and in the same name space, except
        that:
        — a typedef name may be redefined to denote the same type as it currently does,
          provided that type is not a variably modified type;
        — tags may be redeclared as specified in 6.7.2.3.

    4   All declarations in the same scope that refer to the same object or function shall specify
        compatible types.
        Semantics

    5   A declaration specifies the interpretation and attributes of a set of identifiers. A definition
        of an identifier is a declaration for that identifier that:
        — for an object, causes storage to be reserved for that object;
        — for a function, includes the function body;[119]
        — for an enumeration constant, is the (only) declaration of the identifier;
        — for a typedef name, is the first (or only) declaration of the identifier.

    Footnote 119) Function definitions have a different syntax, described in 6.9.1.

    6   The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
        storage duration, and part of the type of the entities that the declarators denote. The init-
        declarator-list is a comma-separated sequence of declarators, each of which may have
        additional type information, or an initializer, or both. The declarators contain the
        identifiers (if any) being declared.

    7   If an identifier for an object is declared with no linkage, the type for the object shall be
        complete by the end of its declarator, or by the end of its init-declarator if it has an
        initializer; in the case of function parameters (including in prototypes), it is the adjusted
        type (see 6.7.6.3) that is required to be complete.
        Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
        (6.7.9), type names (6.7.7), type qualifiers (6.7.3).

### 6.7.1 [Storage-class specifiers]

    1 Syntax
                storage-class-specifier:
                        typedef
                        extern
                        static
                        _Thread_local
                        auto
                        register
        Constraints

    2   At most, one storage-class specifier may be given in the declaration specifiers in a
        declaration, except that _Thread_local may appear with static or extern.[120]

    Footnote 120) See ‘‘future language directions’’ (6.11.5).

    3   In the declaration of an object with block scope, if the declaration specifiers include
        _Thread_local, they shall also include either static or extern. If
        _Thread_local appears in any declaration of an object, it shall be present in every
        declaration of that object.

    4   _Thread_local shall not appear in the declaration specifiers of a function declaration.
        Semantics

    5   The typedef specifier is called a ‘‘storage-class specifier’’ for syntactic convenience
        only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations
        were discussed in 6.2.2 and 6.2.4.

    6   A declaration of an identifier for an object with storage-class specifier register
        suggests that access to the object be as fast as possible. The extent to which such
        suggestions are effective is implementation-defined.[121]

    Footnote 121) The implementation may treat any register declaration simply as an auto declaration. However,
             whether or not addressable storage is actually used, the address of any part of an object declared with
             storage-class specifier register cannot be computed, either explicitly (by use of the unary &
             operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
             6.3.2.1). Thus, the only operators that can be applied to an array declared with storage-class specifier
             register are sizeof and _Alignof.

    7   The declaration of an identifier for a function that has block scope shall have no explicit
        storage-class specifier other than extern.

    8   If an aggregate or union object is declared with a storage-class specifier other than
        typedef, the properties resulting from the storage-class specifier, except with respect to
        linkage, also apply to the members of the object, and so on recursively for any aggregate
        or union member objects.
        Forward references: type definitions (6.7.8).

### 6.7.2 [Type specifiers]

    1 Syntax
                type-specifier:
                        void
                        char
                        short
                        int
                        long
                        float
                        double
                        signed
                        unsigned
                        _Bool
                        _Complex
                        atomic-type-specifier
                        struct-or-union-specifier
                        enum-specifier
                        typedef-name
        Constraints

    2   At least one type specifier shall be given in the declaration specifiers in each declaration,
        and in the specifier-qualifier list in each struct declaration and type name. Each list of
        type specifiers shall be one of the following multisets (delimited by commas, when there
        is more than one multiset per item); the type specifiers may occur in any order, possibly
        intermixed with the other declaration specifiers.
        — void
        — char
        — signed char
        — unsigned char
        — short, signed short, short int, or signed short int
        — unsigned short, or unsigned short int
        — int, signed, or signed int
        — unsigned, or unsigned int
        — long, signed long, long int, or signed long int
        — unsigned long, or unsigned long int
        — long long, signed long long, long long int, or
          signed long long int
        — unsigned long long, or unsigned long long int
        — float
        — double
        — long double
        — _Bool
        — float _Complex
        — double _Complex
        — long double _Complex
        — atomic type specifier
        — struct or union specifier
        — enum specifier
        — typedef name

    3   The type specifier _Complex shall not be used if the implementation does not support
        complex types (see 6.10.8.3).
        Semantics

    4   Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1
        through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The
        characteristics of the other types are discussed in 6.2.5.

    5   Each of the comma-separated multisets designates the same type, except that for bit-
        fields, it is implementation-defined whether the specifier int designates the same type as
        signed int or the same type as unsigned int.
        Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2),
        structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).

### 6.7.2.1 [Structure and union specifiers]

    1 Syntax
                struct-or-union-specifier:
                         struct-or-union identifieropt { struct-declaration-list }
                         struct-or-union identifier
                struct-or-union:
                        struct
                        union
                struct-declaration-list:
                        struct-declaration
                        struct-declaration-list struct-declaration
                struct-declaration:
                        specifier-qualifier-list struct-declarator-listopt ;
                        static_assert-declaration
                specifier-qualifier-list:
                        type-specifier specifier-qualifier-listopt
                        type-qualifier specifier-qualifier-listopt
                struct-declarator-list:
                        struct-declarator
                        struct-declarator-list , struct-declarator
                struct-declarator:
                        declarator
                        declaratoropt : constant-expression
        Constraints

    2   A struct-declaration that does not declare an anonymous structure or anonymous union
        shall contain a struct-declarator-list.

    3   A structure or union shall not contain a member with incomplete or function type (hence,
        a structure shall not contain an instance of itself, but may contain a pointer to an instance
        of itself), except that the last member of a structure with more than one named member
        may have incomplete array type; such a structure (and any union containing, possibly
        recursively, a member that is such a structure) shall not be a member of a structure or an
        element of an array.

    4   The expression that specifies the width of a bit-field shall be an integer constant
        expression with a nonnegative value that does not exceed the width of an object of the
        type that would be specified were the colon and expression omitted.[122] If the value is
        zero, the declaration shall have no declarator.

    Footnote 122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and
             value bits) of a _Bool may be just 1 bit.

    5   A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
        int, unsigned int, or some other implementation-defined type. It is
        implementation-defined whether atomic types are permitted.
         Semantics

    6    As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
         storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
         of members whose storage overlap.

    7    Structure and union specifiers have the same form. The keywords struct and union
         indicate that the type being specified is, respectively, a structure type or a union type.

    8    The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
         within a translation unit. The struct-declaration-list is a sequence of declarations for the
         members of the structure or union. If the struct-declaration-list does not contain any
         named members, either directly or via an anonymous structure or anonymous union, the
         behavior is undefined. The type is incomplete until immediately after the } that
         terminates the list, and complete thereafter.

    9    A member of a structure or union may have any complete object type other than a
         variably modified type.[123] In addition, a member may be declared to consist of a
         specified number of bits (including a sign bit, if any). Such a member is called a
         bit-field;[124] its width is preceded by a colon.

    Footnote 123) A structure or union cannot contain a member with a variably modified type because member names
              are not ordinary identifiers as defined in 6.2.3.

    Footnote 124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to
              or arrays of bit-field objects.

    10   A bit-field is interpreted as having a signed or unsigned integer type consisting of the
         specified number of bits.[125] If the value 0 or 1 is stored into a nonzero-width bit-field of
         type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool
         bit-field has the semantics of a _Bool.

    Footnote 125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
              then it is implementation-defined whether the bit-field is signed or unsigned.

    11   An implementation may allocate any addressable storage unit large enough to hold a bit-
         field. If enough space remains, a bit-field that immediately follows another bit-field in a
         structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
         whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
         implementation-defined. The order of allocation of bit-fields within a unit (high-order to
         low-order or low-order to high-order) is implementation-defined. The alignment of the
         addressable storage unit is unspecified.

    12   A bit-field declaration with no declarator, but only a colon and a width, indicates an
         unnamed bit-field.[126] As a special case, a bit-field structure member with a width of 0
         indicates that no further bit-field is to be packed into the unit in which the previous bit-
         field, if any, was placed.

    Footnote 126) An unnamed bit-field structure member is useful for padding to conform to externally imposed
              layouts.

    13   An unnamed member whose type specifier is a structure specifier with no tag is called an
         anonymous structure; an unnamed member whose type specifier is a union specifier with
         no tag is called an anonymous union. The members of an anonymous structure or union
         are considered to be members of the containing structure or union. This applies
         recursively if the containing structure or union is also anonymous.

    14   Each non-bit-field member of a structure or union object is aligned in an implementation-
         defined manner appropriate to its type.

    15   Within a structure object, the non-bit-field members and the units in which bit-fields
         reside have addresses that increase in the order in which they are declared. A pointer to a
         structure object, suitably converted, points to its initial member (or if that member is a
         bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
         padding within a structure object, but not at its beginning.

    16   The size of a union is sufficient to contain the largest of its members. The value of at
         most one of the members can be stored in a union object at any time. A pointer to a
         union object, suitably converted, points to each of its members (or if a member is a bit-
         field, then to the unit in which it resides), and vice versa.

    17   There may be unnamed padding at the end of a structure or union.

    18   As a special case, the last element of a structure with more than one named member may
         have an incomplete array type; this is called a flexible array member. In most situations,
         the flexible array member is ignored. In particular, the size of the structure is as if the
         flexible array member were omitted except that it may have more trailing padding than
         the omission would imply. However, when a . (or ->) operator has a left operand that is
         (a pointer to) a structure with a flexible array member and the right operand names that
         member, it behaves as if that member were replaced with the longest array (with the same
         element type) that would not make the structure larger than the object being accessed; the
         offset of the array shall remain that of the flexible array member, even if this would differ
         from that of the replacement array. If this array would have no elements, it behaves as if
         it had one element but the behavior is undefined if any attempt is made to access that
         element or to generate a pointer one past it.

    19   EXAMPLE 1    The following illustrates anonymous structures and unions:
                struct v {
                      union {      // anonymous union
                             struct { int i, j; };    // anonymous structure
                             struct { long k, l; } w;
                      };
                      int m;
                } v1;
                  v1.i = 2;   // valid
                  v1.k = 3;   // invalid: inner structure is not anonymous
                  v1.w.k = 5; // valid

    20   EXAMPLE 2          After the declaration:
                  struct s { int n; double d[]; };
         the structure struct s has a flexible array member d. A typical way to use this is:
                  int m = /* some value */;
                  struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
         and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
         p had been declared as:
                  struct { int n; double d[m]; } *p;
         (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
         not be the same).

    21   Following the above declaration:
                  struct s t1 = { 0 };                         // valid
                  struct s t2 = { 1, { 4.2 }};                 // invalid
                  t1.n = 4;                                    // valid
                  t1.d[0] = 4.2;                               // might be undefined behavior
         The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
         contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
                  sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
         in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
         code.

    22   After the further declaration:
                  struct ss { int n; };
         the expressions:
                  sizeof (struct s) >= sizeof (struct ss)
                  sizeof (struct s) >= offsetof(struct s, d)
         are always equal to 1.

    23   If sizeof (double) is 8, then after the following code is executed:
                  struct s *s1;
                  struct s *s2;
                  s1 = malloc(sizeof (struct s) + 64);
                  s2 = malloc(sizeof (struct s) + 46);
         and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
         purposes, as if the identifiers had been declared as:
                  struct { int n; double d[8]; } *s1;
                  struct { int n; double d[5]; } *s2;

    24   Following the further successful assignments:
                  s1 = malloc(sizeof (struct s) + 10);
                  s2 = malloc(sizeof (struct s) + 6);
         they then behave as if the declarations were:
                  struct { int n; double d[1]; } *s1, *s2;
         and:
                  double *dp;
                  dp = &(s1->d[0]); // valid
                  *dp = 42;         // valid
                  dp = &(s2->d[0]); // valid
                  *dp = 42;         // undefined behavior

    25   The assignment:
                  *s1 = *s2;
         only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
         of the structure, they might be copied or simply overwritten with indeterminate values.

    26   EXAMPLE 3 Because members of anonymous structures and unions are considered to be members of the
         containing structure or union, struct s in the following example has more than one named member and
         thus the use of a flexible array member is valid:
                  struct s {
                        struct { int i; };
                        int a[];
                  };

         Forward references: declarators (6.7.6), tags (6.7.2.3).

### 6.7.2.2 [Enumeration specifiers]

    1 Syntax
                 enum-specifier:
                        enum identifieropt { enumerator-list }
                        enum identifieropt { enumerator-list , }
                        enum identifier
                  enumerator-list:
                        enumerator
                        enumerator-list , enumerator
                  enumerator:
                        enumeration-constant
                        enumeration-constant = constant-expression
         Constraints

    2    The expression that defines the value of an enumeration constant shall be an integer
         constant expression that has a value representable as an int.
        Semantics

    3   The identifiers in an enumerator list are declared as constants that have type int and
        may appear wherever such are permitted.[127] An enumerator with = defines its
        enumeration constant as the value of the constant expression. If the first enumerator has
        no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
        defines its enumeration constant as the value of the constant expression obtained by
        adding 1 to the value of the previous enumeration constant. (The use of enumerators with
        = may produce enumeration constants with values that duplicate other values in the same
        enumeration.) The enumerators of an enumeration are also known as its members.

    Footnote 127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
             each other and from other identifiers declared in ordinary declarators.

    4   Each enumerated type shall be compatible with char, a signed integer type, or an
        unsigned integer type. The choice of type is implementation-defined,[128] but shall be
        capable of representing the values of all the members of the enumeration. The
        enumerated type is incomplete until immediately after the } that terminates the list of
        enumerator declarations, and complete thereafter.

    Footnote 128) An implementation may delay the choice of which integer type until all enumeration constants have
             been seen.

    5   EXAMPLE       The following fragment:
                enum hue { chartreuse, burgundy, claret=20, winedark };
                enum hue col, *cp;
                col = claret;
                cp = &col;
                if (*cp != burgundy)
                      /* ... */
        makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
        pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.

        Forward references: tags (6.7.2.3).

### 6.7.2.3 [Tags]

    1 Constraints
       A specific type shall have its content defined at most once.

    2   Where two declarations that use the same tag declare the same type, they shall both use
        the same choice of struct, union, or enum.

    3   A type specifier of the form
                enum identifier
        without an enumerator list shall only appear after the type it specifies is complete.
        Semantics

    4   All declarations of structure, union, or enumerated types that have the same scope and
        use the same tag declare the same type. Irrespective of whether there is a tag or what
        other declarations of the type are in the same translation unit, the type is incomplete[129]
        until immediately after the closing brace of the list defining the content, and complete
        thereafter.

    Footnote 129) An incomplete type may only by used when the size of an object of that type is not needed. It is not
             needed, for example, when a typedef name is declared to be a specifier for a structure or union, or
             when a pointer to or a function returning a structure or union is being declared. (See incomplete types
             in 6.2.5.) The specification has to be complete before such a function is called or defined.

    5   Two declarations of structure, union, or enumerated types which are in different scopes or
        use different tags declare distinct types. Each declaration of a structure, union, or
        enumerated type which does not include a tag declares a distinct type.

    6   A type specifier of the form
                 struct-or-union identifieropt { struct-declaration-list }
        or
                 enum identifieropt { enumerator-list }
        or
                 enum identifieropt { enumerator-list , }
        declares a structure, union, or enumerated type. The list defines the structure content,
        union content, or enumeration content. If an identifier is provided,[130] the type specifier
        also declares the identifier to be the tag of that type.

    Footnote 130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration
             of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
             can make use of that typedef name to declare objects having the specified structure, union, or
             enumerated type.

    7   A declaration of the form
                 struct-or-union identifier ;
        specifies a structure or union type and declares the identifier as a tag of that type.[131]

    Footnote 131) A similar construction with enum does not exist.

    8   If a type specifier of the form
                 struct-or-union identifier
        occurs other than as part of one of the above forms, and no other declaration of the
        identifier as a tag is visible, then it declares an incomplete structure or union type, and
        declares the identifier as the tag of that type.[131]

    Footnote 131) A similar construction with enum does not exist.

    9    If a type specifier of the form
                  struct-or-union identifier
         or
                  enum identifier
         occurs other than as part of one of the above forms, and a declaration of the identifier as a
         tag is visible, then it specifies the same type as that other declaration, and does not
         redeclare the tag.

    10   EXAMPLE 1       This mechanism allows declaration of a self-referential structure.
                  struct tnode {
                        int count;
                        struct tnode *left, *right;
                  };
         specifies a structure that contains an integer and two pointers to objects of the same type. Once this
         declaration has been given, the declaration
                  struct tnode s, *sp;
         declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
         these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
         which sp points; the expression s.right->count designates the count member of the right struct
         tnode pointed to from s.

    11   The following alternative formulation uses the typedef mechanism:
                  typedef struct tnode TNODE;
                  struct tnode {
                        int count;
                        TNODE *left, *right;
                  };
                  TNODE s, *sp;

    12   EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
         structures, the declarations
                  struct s1 { struct s2 *s2p; /* ... */ }; // D1
                  struct s2 { struct s1 *s1p; /* ... */ }; // D2
         specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
         declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
         D2. To eliminate this context sensitivity, the declaration
                 struct s2;
         may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
         completes the specification of the new type.

         Forward references: declarators (6.7.6), type definitions (6.7.8).

### 6.7.2.4 [Atomic type specifiers]

    1 Syntax
                atomic-type-specifier:
                        _Atomic ( type-name )
        Constraints

    2   Atomic type specifiers shall not be used if the implementation does not support atomic
        types (see 6.10.8.3).

    3   The type name in an atomic type specifier shall not refer to an array type, a function type,
        an atomic type, or a qualified type.
        Semantics

    4   The properties associated with atomic types are meaningful only for expressions that are
        lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is
        interpreted as a type specifier (with a type name), not as a type qualifier.

### 6.7.3 [Type qualifiers]

    1 Syntax
                type-qualifier:
                        const
                        restrict
                        volatile
                        _Atomic
        Constraints

    2   Types other than pointer types whose referenced type is an object type shall not be
        restrict-qualified.

    3   The type modified by the _Atomic qualifier shall not be an array type or a function
        type.
        Semantics

    4   The properties associated with qualified types are meaningful only for expressions that
        are lvalues.[132]

    Footnote 132) The implementation may place a const object that is not volatile in a read-only region of
             storage. Moreover, the implementation need not allocate storage for such an object if its address is
             never used.

    5   If the same qualifier appears more than once in the same specifier-qualifier-list, either
        directly or via one or more typedefs, the behavior is the same as if it appeared only
        once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier-
         list, the resulting type is the so-qualified atomic type.

    6    If an attempt is made to modify an object defined with a const-qualified type through use
         of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
         made to refer to an object defined with a volatile-qualified type through use of an lvalue
         with non-volatile-qualified type, the behavior is undefined.[133]

    Footnote 133) This applies to those objects that behave as if they were defined with qualified types, even if they are
              never actually defined as objects in the program (such as an object at a memory-mapped input/output
              address).

    7    An object that has volatile-qualified type may be modified in ways unknown to the
         implementation or have other unknown side effects. Therefore any expression referring
         to such an object shall be evaluated strictly according to the rules of the abstract machine,
         as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
         object shall agree with that prescribed by the abstract machine, except as modified by the
         unknown factors mentioned previously.[134] What constitutes an access to an object that
         has volatile-qualified type is implementation-defined.

    Footnote 134) A volatile declaration may be used to describe an object corresponding to a memory-mapped
              input/output port or an object accessed by an asynchronously interrupting function. Actions on
              objects so declared shall not be ‘‘optimized out’’ by an implementation or reordered except as
              permitted by the rules for evaluating expressions.

    8    An object that is accessed through a restrict-qualified pointer has a special association
         with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
         that object use, directly or indirectly, the value of that particular pointer.[135] The intended
         use of the restrict qualifier (like the register storage class) is to promote
         optimization, and deleting all instances of the qualifier from all preprocessing translation
         units composing a conforming program does not change its meaning (i.e., observable
         behavior).

    Footnote 135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this
              association between the allocated object and the pointer.

    9    If the specification of an array type includes any type qualifiers, the element type is so-
         qualified, not the array type. If the specification of a function type includes any type
         qualifiers, the behavior is undefined.[136]

    Footnote 136) Both of these can occur through the use of typedefs.

    10   For two qualified types to be compatible, both shall have the identically qualified version
         of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
         does not affect the specified type.

    11   EXAMPLE 1       An object declared
                  extern const volatile int real_time_clock;
         may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.

    12   EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
         modify an aggregate type:
                  const struct s { int mem; } cs = { 1 };
                  struct s ncs; // the object ncs is modifiable
                  typedef int A[2][3];
                  const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
                  int *pi;
                  const int *pci;
                  ncs = cs;      // valid
                  cs = ncs;      // violates modifiable lvalue constraint for =
                  pi = &ncs.mem; // valid
                  pi = &cs.mem; // violates type constraints for =
                  pci = &cs.mem; // valid
                  pi = a[0];     // invalid: a[0] has type ‘‘const int *’’

    13   EXAMPLE 3        The declaration
                  _Atomic volatile int *p;
         specifies that p has the type ‘‘pointer to volatile atomic int’’, a pointer to a volatile-qualified atomic type.

### 6.7.3.1 [Formal definition of restrict]

    1    Let D be a declaration of an ordinary identifier that provides a means of designating an
         object P as a restrict-qualified pointer to type T.

    2    If D appears inside a block and does not have storage class extern, let B denote the
         block. If D appears in the list of parameter declarations of a function definition, let B
         denote the associated block. Otherwise, let B denote the block of main (or the block of
         whatever function is called at program startup in a freestanding environment).

    3    In what follows, a pointer expression E is said to be based on object P if (at some
         sequence point in the execution of B prior to the evaluation of E) modifying P to point to
         a copy of the array object into which it formerly pointed would change the value of E.[137]
         Note that ‘‘based’’ is defined only for expressions with pointer types.

    Footnote 137) In other words, E depends on the value of P itself rather than on the value of an object referenced
              indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
              expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
              expressions *p and p[1] are not.

    4    During each execution of B, let L be any lvalue that has &L based on P. If L is used to
         access the value of the object X that it designates, and X is also modified (by any means),
         then the following requirements apply: T shall not be const-qualified. Every other lvalue
         used to access the value of X shall also have its address based on P. Every access that
         modifies X shall be considered also to modify P, for the purposes of this subclause. If P
         is assigned the value of a pointer expression E that is based on another restricted pointer
         object P2, associated with block B2, then either the execution of B2 shall begin before
         the execution of B, or the execution of B2 shall end prior to the assignment. If these
         requirements are not met, then the behavior is undefined.

    5    Here an execution of B means that portion of the execution of the program that would
         correspond to the lifetime of an object with scalar type and automatic storage duration
         associated with B.

    6    A translator is free to ignore any or all aliasing implications of uses of restrict.

    7    EXAMPLE 1       The file scope declarations
                  int * restrict a;
                  int * restrict b;
                  extern int c[];
         assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
         program, then it is never accessed using either of the other two.

    8    EXAMPLE 2       The function parameter declarations in the following example
                  void f(int n, int * restrict p, int * restrict q)
                  {
                        while (n-- > 0)
                              *p++ = *q++;
                  }
         assert that, during each execution of the function, if an object is accessed through one of the pointer
         parameters, then it is not also accessed through the other.

    9    The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
         analysis of function f without examining any of the calls of f in the program. The cost is that the
         programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
         second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
         both p and q.
                  void g(void)
                  {
                        extern int d[100];
                        f(50, d + 50, d); // valid
                        f(50, d + 1, d); // undefined behavior
                  }

    10   EXAMPLE 3       The function parameter declarations
                  void h(int n, int * restrict p, int * restrict q, int * restrict r)
                  {
                        int i;
                        for (i = 0; i < n; i++)
                               p[i] = q[i] + r[i];
                  }
         illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
         are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
         modified within function h.

    11   EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
         function call and an equivalent nested block. With one exception, only ‘‘outer-to-inner’’ assignments
         between restricted pointers declared in nested blocks have defined behavior.
                  {
                           int * restrict p1;
                           int * restrict q1;
                           p1 = q1; // undefined behavior
                           {
                                 int * restrict p2 = p1; // valid
                                 int * restrict q2 = q1; // valid
                                 p1 = q2;                 // undefined behavior
                                 p2 = q2;                 // undefined behavior
                           }
                  }

    12   The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
         precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
         example, this permits new_vector to return a vector.
                  typedef struct { int n; float * restrict v; } vector;
                  vector new_vector(int n)
                  {
                        vector t;
                        t.n = n;
                        t.v = malloc(n * sizeof (float));
                        return t;
                  }

### 6.7.4 [Function specifiers]

    1 Syntax
                 function-specifier:
                         inline
                         _Noreturn
         Constraints

    2    Function specifiers shall be used only in the declaration of an identifier for a function.

    3    An inline definition of a function with external linkage shall not contain a definition of a
         modifiable object with static or thread storage duration, and shall not contain a reference
         to an identifier with internal linkage.

    4    In a hosted environment, no function specifier(s) shall appear in a declaration of main.
         Semantics

    5    A function specifier may appear more than once; the behavior is the same as if it
         appeared only once.

    6    A function declared with an inline function specifier is an inline function. Making a
         function an inline function suggests that calls to the function be as fast as possible.[138]
         The extent to which such suggestions are effective is implementation-defined.[139]

    Footnote 138) By using, for example, an alternative to the usual function call mechanism, such as ‘‘inline
              substitution’’. Inline substitution is not textual substitution, nor does it create a new function.
              Therefore, for example, the expansion of a macro used within the body of the function uses the
              definition it had at the point the function body appears, and not where the function is called; and
              identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a
              single address, regardless of the number of inline definitions that occur in addition to the external
              definition.

    Footnote 139) For example, an implementation might never perform inline substitution, or might only perform inline
              substitutions to calls in the scope of an inline declaration.

    7    Any function with internal linkage can be an inline function. For a function with external
         linkage, the following restrictions apply: If a function is declared with an inline
         function specifier, then it shall also be defined in the same translation unit. If all of the
         file scope declarations for a function in a translation unit include the inline function
         specifier without extern, then the definition in that translation unit is an inline
         definition. An inline definition does not provide an external definition for the function,
         and does not forbid an external definition in another translation unit. An inline definition
         provides an alternative to an external definition, which a translator may use to implement
         any call to the function in the same translation unit. It is unspecified whether a call to the
         function uses the inline definition or the external definition.[140]

    Footnote 140) Since an inline definition is distinct from the corresponding external definition and from any other
              corresponding inline definitions in other translation units, all corresponding objects with static storage
              duration are also distinct in each of the definitions.

    8    A function declared with a _Noreturn function specifier shall not return to its caller.
         Recommended practice

    9    The implementation should produce a diagnostic message for a function declared with a
         _Noreturn function specifier that appears to be capable of returning to its caller.

    10   EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
         definition, or a definition available for use only within the translation unit. A file scope declaration with
         extern creates an external definition. The following example shows an entire translation unit.
                  inline double fahr(double t)
                  {
                        return (9.0 * t) / 5.0 + 32.0;
                  }
                  inline double cels(double t)
                  {
                        return (5.0 * (t - 32.0)) / 9.0;
                  }
                  extern double fahr(double);                   // creates an external definition
                  double convert(int is_fahr, double temp)
                  {
                        /* A translator may perform inline substitutions */
                        return is_fahr ? cels(temp) : fahr(temp);
                  }

    11   Note that the definition of fahr is an external definition because fahr is also declared with extern, but
         the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
         external definition has to appear in another translation unit (see 6.9); the inline definition and the external
         definition are distinct and either may be used for the call.

    12   EXAMPLE 2
                  _Noreturn void f () {
                        abort(); // ok
                  }
                  _Noreturn void g (int i) { // causes undefined behavior if i <= 0
                        if (i > 0) abort();
                  }

         Forward references: function definitions (6.9.1).

### 6.7.5 [Alignment specifier]

    1 Syntax
                 alignment-specifier:
                         _Alignas ( type-name )
                        _Alignas ( constant-expression )
         Constraints

    2    An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
         a function, or a parameter, or an object declared with the register storage-class
         specifier.

    3    The constant expression shall be an integer constant expression. It shall evaluate to a
         valid fundamental alignment, or to a valid extended alignment supported by the
         implementation in the context in which it appears, or to zero.

    4    The combined effect of all alignment attributes in a declaration shall not specify an
         alignment that is less strict than the alignment that would otherwise be required for the
         type of the object or member being declared.
         Semantics

    5    The first form is equivalent to _Alignas (_Alignof (type-name)).

    6    The alignment requirement of the declared object or member is taken to be the specified
         alignment. An alignment specification of zero has no effect.[141] When multiple
         alignment specifiers occur in a declaration, the effective alignment requirement is the
         strictest specified alignment.

    Footnote 141) An alignment specification of zero also does not affect other alignment specifications in the same
             declaration.

    7   If the definition of an object has an alignment specifier, any other declaration of that
        object shall either specify equivalent alignment or have no alignment specifier. If the
        definition of an object does not have an alignment specifier, any other declaration of that
        object shall also have no alignment specifier. If declarations of an object in different
        translation units have different alignment specifiers, the behavior is undefined.

### 6.7.6 [Declarators]

    1 Syntax
                declarator:
                        pointeropt direct-declarator
                 direct-declarator:
                         identifier
                         ( declarator )
                         direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
                         direct-declarator [ static type-qualifier-listopt assignment-expression ]
                         direct-declarator [ type-qualifier-list static assignment-expression ]
                         direct-declarator [ type-qualifier-listopt * ]
                         direct-declarator ( parameter-type-list )
                         direct-declarator ( identifier-listopt )
                 pointer:
                        * type-qualifier-listopt
                        * type-qualifier-listopt pointer
                 type-qualifier-list:
                        type-qualifier
                        type-qualifier-list type-qualifier
                 parameter-type-list:
                       parameter-list
                       parameter-list , ...
                 parameter-list:
                       parameter-declaration
                       parameter-list , parameter-declaration
                 parameter-declaration:
                       declaration-specifiers declarator
                       declaration-specifiers abstract-declaratoropt
                identifier-list:
                        identifier
                        identifier-list , identifier
        Semantics

    2   Each declarator declares one identifier, and asserts that when an operand of the same
        form as the declarator appears in an expression, it designates a function or object with the
        scope, storage duration, and type indicated by the declaration specifiers.

    3   A full declarator is a declarator that is not part of another declarator. The end of a full
        declarator is a sequence point. If, in the nested sequence of declarators in a full
        declarator, there is a declarator specifying a variable length array type, the type specified
        by the full declarator is said to be variably modified. Furthermore, any type derived by
        declarator type derivation from a variably modified type is itself variably modified.

    4   In the following subclauses, consider a declaration
                T D1
        where T contains the declaration specifiers that specify a type T (such as int) and D1 is
        a declarator that contains an identifier ident. The type specified for the identifier ident in
        the various forms of declarator is described inductively using this notation.

    5   If, in the declaration ‘‘T D1’’, D1 has the form
                identifier
        then the type specified for ident is T .

    6   If, in the declaration ‘‘T D1’’, D1 has the form
                ( D )
        then ident has the type specified by the declaration ‘‘T D’’. Thus, a declarator in
        parentheses is identical to the unparenthesized declarator, but the binding of complicated
        declarators may be altered by parentheses.
        Implementation limits

    7   As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
        function declarators that modify an arithmetic, structure, union, or void type, either
        directly or via one or more typedefs.
        Forward references: array declarators (6.7.6.2), type definitions (6.7.8).

### 6.7.6.1 [Pointer declarators]

    1 Semantics
       If, in the declaration ‘‘T D1’’, D1 has the form
                * type-qualifier-listopt D
        and the type specified for ident in the declaration ‘‘T D’’ is ‘‘derived-declarator-type-list
        T ’’, then the type specified for ident is ‘‘derived-declarator-type-list type-qualifier-list
        pointer to T ’’. For each type qualifier in the list, ident is a so-qualified pointer.

    2   For two pointer types to be compatible, both shall be identically qualified and both shall
        be pointers to compatible types.

    3   EXAMPLE The following pair of declarations demonstrates the difference between a ‘‘variable pointer
        to a constant value’’ and a ‘‘constant pointer to a variable value’’.
                const int *ptr_to_constant;
                int *const constant_ptr;
        The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
        but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
        int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
        same location.

    4   The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
        type ‘‘pointer to int’’.
                typedef int *int_ptr;
                const int_ptr constant_ptr;
        declares constant_ptr as an object that has type ‘‘const-qualified pointer to int’’.

### 6.7.6.2 [Array declarators]

    1 Constraints
       In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
        an expression or *. If they delimit an expression (which specifies the size of an array), the
        expression shall have an integer type. If the expression is a constant expression, it shall
        have a value greater than zero. The element type shall not be an incomplete or function
        type. The optional type qualifiers and the keyword static shall appear only in a
        declaration of a function parameter with an array type, and then only in the outermost
        array type derivation.

    2   If an identifier is declared as having a variably modified type, it shall be an ordinary
        identifier (as defined in 6.2.3), have no linkage, and have either block scope or function
        prototype scope. If an identifier is declared to be an object with static or thread storage
        duration, it shall not have a variable length array type.
        Semantics

    3   If, in the declaration ‘‘T D1’’, D1 has one of the forms:
                 D[ type-qualifier-listopt assignment-expressionopt ]
                 D[ static type-qualifier-listopt assignment-expression ]
                 D[ type-qualifier-list static assignment-expression ]
                 D[ type-qualifier-listopt * ]
        and the type specified for ident in the declaration ‘‘T D’’ is ‘‘derived-declarator-type-list
        T ’’, then the type specified for ident is ‘‘derived-declarator-type-list array of T ’’.[142]
        (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)

    Footnote 142) When several ‘‘array of’’ specifications are adjacent, a multidimensional array is declared.

    4   If the size is not present, the array type is an incomplete type. If the size is * instead of
        being an expression, the array type is a variable length array type of unspecified size,
        which can only be used in declarations or type names with function prototype scope;[143]
        such arrays are nonetheless complete types. If the size is an integer constant expression
        and the element type has a known constant size, the array type is not a variable length
        array type; otherwise, the array type is a variable length array type. (Variable length
        arrays are a conditional feature that implementations need not support; see 6.10.8.3.)

    Footnote 143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3).

    5   If the size is an expression that is not an integer constant expression: if it occurs in a
        declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
        each time it is evaluated it shall have a value greater than zero. The size of each instance
        of a variable length array type does not change during its lifetime. Where a size
        expression is part of the operand of a sizeof operator and changing the value of the
        size expression would not affect the result of the operator, it is unspecified whether or not
        the size expression is evaluated.

    6   For two array types to be compatible, both shall have compatible element types, and if
        both size specifiers are present, and are integer constant expressions, then both size
        specifiers shall have the same constant value. If the two array types are used in a context
        which requires them to be compatible, it is undefined behavior if the two size specifiers
        evaluate to unequal values.

    7   EXAMPLE 1
                 float fa[11], *afp[17];
        declares an array of float numbers and an array of pointers to float numbers.

    8   EXAMPLE 2       Note the distinction between the declarations
                  extern int *x;
                  extern int y[];
         The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
         (an incomplete type), the storage for which is defined elsewhere.

    9    EXAMPLE 3       The following declarations demonstrate the compatibility rules for variably modified types.
                  extern int n;
                  extern int m;
                  void fcompat(void)
                  {
                        int a[n][6][m];
                        int (*p)[4][n+1];
                        int c[n][n][6][m];
                        int (*r)[n][n][n+1];
                        p = a;       // invalid: not compatible because 4 != 6
                        r = c;       // compatible, but defined behavior only if
                                     // n == 6 and m == n+1
                  }

    10   EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
         function prototype scope. Array objects declared with the _Thread_local, static, or extern
         storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
         the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
         identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
         structures or unions.
                  extern int n;
                  int A[n];                                             // invalid: file scope VLA
                  extern int (*p2)[n];                                  // invalid: file scope VM
                  int B[100];                                           // valid: file scope but not VM
                  void fvla(int m, int C[m][m]);                        // valid: VLA with prototype scope
                  void fvla(int m, int C[m][m])                         // valid: adjusted to auto pointer to VLA
                  {
                        typedef int VLA[m][m];                          // valid: block scope typedef VLA
                           struct tag {
                                 int (*y)[n];                           // invalid: y not ordinary identifier
                                 int z[n];                              // invalid: z not ordinary identifier
                           };
                           int D[m];                                    // valid: auto VLA
                           static int E[m];                             // invalid: static block scope VLA
                           extern int F[m];                             // invalid: F has linkage and is VLA
                           int (*s)[m];                                 // valid: auto pointer to VLA
                           extern int (*r)[m];                          // invalid: r has linkage and points to VLA
                           static int (*q)[m] = &B;                     // valid: q is a static block pointer to VLA
                  }

         Forward references:           function declarators (6.7.6.3), function definitions (6.9.1),
         initialization (6.7.9).

### 6.7.6.3 [Function declarators (including prototypes)]

    1 Constraints
        A function declarator shall not specify a return type that is a function type or an array
         type.

    2    The only storage-class specifier that shall occur in a parameter declaration is register.

    3    An identifier list in a function declarator that is not part of a definition of that function
         shall be empty.

    4    After adjustment, the parameters in a parameter type list in a function declarator that is
         part of a definition of that function shall not have incomplete type.
         Semantics

    5    If, in the declaration ‘‘T D1’’, D1 has the form
                D( parameter-type-list )
         or
                D( identifier-listopt )
         and the type specified for ident in the declaration ‘‘T D’’ is ‘‘derived-declarator-type-list
         T ’’, then the type specified for ident is ‘‘derived-declarator-type-list function returning
         T ’’.

    6    A parameter type list specifies the types of, and may declare identifiers for, the
         parameters of the function.

    7    A declaration of a parameter as ‘‘array of type’’ shall be adjusted to ‘‘qualified pointer to
         type’’, where the type qualifiers (if any) are those specified within the [ and ] of the
         array type derivation. If the keyword static also appears within the [ and ] of the
         array type derivation, then for each call to the function, the value of the corresponding
         actual argument shall provide access to the first element of an array with at least as many
         elements as specified by the size expression.

    8    A declaration of a parameter as ‘‘function returning type’’ shall be adjusted to ‘‘pointer to
         function returning type’’, as in 6.3.2.1.

    9    If the list terminates with an ellipsis (, ...), no information about the number or types
         of the parameters after the comma is supplied.[144]

    Footnote 144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
              correspond to the ellipsis.

    10   The special case of an unnamed parameter of type void as the only item in the list
         specifies that the function has no parameters.

    11   If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
         parameter name, it shall be taken as a typedef name.

    12   If the function declarator is not part of a definition of that function, parameters may have
         incomplete type and may use the [*] notation in their sequences of declarator specifiers
         to specify variable length array types.

    13   The storage-class specifier in the declaration specifiers for a parameter declaration, if
         present, is ignored unless the declared parameter is one of the members of the parameter
         type list for a function definition.

    14   An identifier list declares only the identifiers of the parameters of the function. An empty
         list in a function declarator that is part of a definition of that function specifies that the
         function has no parameters. The empty list in a function declarator that is not part of a
         definition of that function specifies that no information about the number or types of the
         parameters is supplied.[145]

    Footnote 145) See ‘‘future language directions’’ (6.11.6).

    15   For two function types to be compatible, both shall specify compatible return types.[146]
         Moreover, the parameter type lists, if both are present, shall agree in the number of
         parameters and in use of the ellipsis terminator; corresponding parameters shall have
         compatible types. If one type has a parameter type list and the other type is specified by a
         function declarator that is not part of a function definition and that contains an empty
         identifier list, the parameter list shall not have an ellipsis terminator and the type of each
         parameter shall be compatible with the type that results from the application of the
         default argument promotions. If one type has a parameter type list and the other type is
         specified by a function definition that contains a (possibly empty) identifier list, both shall
         agree in the number of parameters, and the type of each prototype parameter shall be
         compatible with the type that results from the application of the default argument
         promotions to the type of the corresponding identifier. (In the determination of type
         compatibility and of a composite type, each parameter declared with function or array
         type is taken as having the adjusted type and each parameter declared with qualified type
         is taken as having the unqualified version of its declared type.)

    Footnote 146) If both function types are ‘‘old style’’, parameter types are not compared.

    16   EXAMPLE 1       The declaration
                  int f(void), *fip(), (*pfi)();
         declares a function f with no parameters returning an int, a function fip with no parameter specification
         returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
         int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
         declaration suggests, and the same construction in an expression requires, the calling of a function fip,
         and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
         extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
         designator, which is then used to call the function; it returns an int.

    17   If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
         declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
         internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
         the identifier of the pointer pfi has block scope and no linkage.

    18   EXAMPLE 2       The declaration
                   int (*apfi[3])(int *x, int *y);
         declares an array apfi of three pointers to functions returning int. Each of these functions has two
         parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
         go out of scope at the end of the declaration of apfi.

    19   EXAMPLE 3       The declaration
                   int (*fpfi(int (*)(long), int))(int, ...);
         declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
         parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
         The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
         additional arguments of any type.

    20   EXAMPLE 4       The following prototype has a variably modified parameter.
                   void addscalar(int n, int m,
                         double a[n][n*m+300], double x);
                   int main()
                   {
                         double b[4][308];
                         addscalar(4, 2, b, 2.17);
                         return 0;
                   }
                   void addscalar(int n, int m,
                         double a[n][n*m+300], double x)
                   {
                         for (int i = 0; i < n; i++)
                               for (int j = 0, k = n*m+300; j < k; j++)
                                     // a is a pointer to a VLA with n*m+300 elements
                                     a[i][j] += x;
                   }

    21   EXAMPLE 5       The following are all compatible function prototype declarators.
                   double maximum(int n, int m, double a[n][m]);
                   double maximum(int n, int m, double a[*][*]);
                   double maximum(int n, int m, double a[ ][*]);
                   double maximum(int n, int m, double a[ ][m]);
         as are:
                   void f(double (* restrict a)[5]);
                   void f(double a[restrict][5]);
                   void f(double a[restrict 3][5]);
                   void f(double a[restrict static 3][5]);
        (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
        non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)

        Forward references: function definitions (6.9.1), type names (6.7.7).

### 6.7.7 [Type names]

    1 Syntax
                type-name:
                        specifier-qualifier-list abstract-declaratoropt
                 abstract-declarator:
                        pointer
                        pointeropt direct-abstract-declarator
                 direct-abstract-declarator:
                         ( abstract-declarator )
                         direct-abstract-declaratoropt [ type-qualifier-listopt
                                        assignment-expressionopt ]
                         direct-abstract-declaratoropt [ static type-qualifier-listopt
                                        assignment-expression ]
                         direct-abstract-declaratoropt [ type-qualifier-list static
                                        assignment-expression ]
                         direct-abstract-declaratoropt [ * ]
                         direct-abstract-declaratoropt ( parameter-type-listopt )
        Semantics

    2   In several contexts, it is necessary to specify a type. This is accomplished using a type
        name, which is syntactically a declaration for a function or an object of that type that
        omits the identifier.[147]

    Footnote 147) As indicated by the syntax, empty parentheses in a type name are interpreted as ‘‘function with no
             parameter specification’’, rather than redundant parentheses around the omitted identifier.

    3   EXAMPLE        The constructions
                 (a)      int
                 (b)      int *
                 (c)      int *[3]
                 (d)      int (*)[3]
                 (e)      int (*)[*]
                 (f)      int *()
                 (g)      int (*)(void)
                 (h)      int (*const [])(unsigned int, ...)
        name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
        array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
        with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
        returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
        parameter that has type unsigned int and an unspecified number of other parameters, returning an
        int.

### 6.7.8 [Type definitions]

    1 Syntax
                typedef-name:
                        identifier
        Constraints

    2   If a typedef name specifies a variably modified type then it shall have block scope.
        Semantics

    3   In a declaration whose storage-class specifier is typedef, each declarator defines an
        identifier to be a typedef name that denotes the type specified for the identifier in the way
        described in 6.7.6. Any array size expressions associated with variable length array
        declarators are evaluated each time the declaration of the typedef name is reached in the
        order of execution. A typedef declaration does not introduce a new type, only a
        synonym for the type so specified. That is, in the following declarations:
                 typedef T type_ident;
                 type_ident D;
        type_ident is defined as a typedef name with the type specified by the declaration
        specifiers in T (known as T ), and the identifier in D has the type ‘‘derived-declarator-
        type-list T ’’ where the derived-declarator-type-list is specified by the declarators of D. A
        typedef name shares the same name space as other identifiers declared in ordinary
        declarators.

    4   EXAMPLE 1       After
                 typedef int MILES, KLICKSP();
                 typedef struct { double hi, lo; } range;
        the constructions
                 MILES distance;
                 extern KLICKSP *metricp;
                 range x;
                 range z, *zp;
        are all valid declarations. The type of distance is int, that of metricp is ‘‘pointer to function with no
        parameter specification returning int’’, and that of x and z is the specified structure; zp is a pointer to
        such a structure. The object distance has a type compatible with any other int object.

    5   EXAMPLE 2       After the declarations
                 typedef struct s1 { int x; } t1, *tp1;
                 typedef struct s2 { int x; } t2, *tp2;
        type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
        s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.

    6   EXAMPLE 3       The following obscure constructions
                 typedef signed int t;
                 typedef int plain;
                 struct tag {
                       unsigned t:4;
                       const t:5;
                       plain r:5;
                 };
        declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
        with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
        qualified bit-field which (if it could be accessed) would contain values in either the range [−15, +15] or
        [−16, +15], and one named r that contains values in one of the ranges [0, 31], [−15, +15], or [−16, +15].
        (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
        unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
        type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
        in an inner scope by
                 t f(t (t));
                 long t;
        then a function f is declared with type ‘‘function returning signed int with one unnamed parameter
        with type pointer to function returning signed int with one unnamed parameter with type signed
        int’’, and an identifier t with type long int.

    7   EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
        following declarations of the signal function specify exactly the same type, the first without making use
        of any typedef names.
                 typedef void fv(int), (*pfv)(int);
                 void (*signal(int, void (*)(int)))(int);
                 fv *signal(int, fv *);
                 pfv signal(int, pfv);

    8   EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
        time the typedef name is defined, not each time it is used:
                 void copyt(int n)
                 {
                       typedef int B[n];   // B is n ints, n evaluated now
                       n += 1;
                       B a;                // a is n ints, n without += 1
                       int b[n];           // a and b are different sizes
                       for (int i = 1; i < n; i++)
                             a[i-1] = b[i];
                 }

### 6.7.9 [Initialization]

    1 Syntax
                initializer:
                          assignment-expression
                          { initializer-list }
                          { initializer-list , }
                 initializer-list:
                          designationopt initializer
                          initializer-list , designationopt initializer
                 designation:
                        designator-list =
                 designator-list:
                        designator
                        designator-list designator
                 designator:
                        [ constant-expression ]
                        . identifier
        Constraints

    2   No initializer shall attempt to provide a value for an object not contained within the entity
        being initialized.

    3   The type of the entity to be initialized shall be an array of unknown size or a complete
        object type that is not a variable length array type.

    4   All the expressions in an initializer for an object that has static or thread storage duration
        shall be constant expressions or string literals.

    5   If the declaration of an identifier has block scope, and the identifier has external or
        internal linkage, the declaration shall have no initializer for the identifier.

    6   If a designator has the form
                 [ constant-expression ]
        then the current object (defined below) shall have array type and the expression shall be
        an integer constant expression. If the array is of unknown size, any nonnegative value is
        valid.

    7   If a designator has the form
                 . identifier
        then the current object (defined below) shall have structure or union type and the
         Semantics

    8    An initializer specifies the initial value stored in an object.

    9    Except where explicitly stated otherwise, for the purposes of this subclause unnamed
         members of objects of structure and union type do not participate in initialization.
         Unnamed members of structure objects have indeterminate value even after initialization.

    10   If an object that has automatic storage duration is not initialized explicitly, its value is
         indeterminate. If an object that has static or thread storage duration is not initialized
         explicitly, then:
         — if it has pointer type, it is initialized to a null pointer;
         — if it has arithmetic type, it is initialized to (positive or unsigned) zero;
         — if it is an aggregate, every member is initialized (recursively) according to these rules,
           and any padding is initialized to zero bits;
         — if it is a union, the first named member is initialized (recursively) according to these
           rules, and any padding is initialized to zero bits;

    11   The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
         initial value of the object is that of the expression (after conversion); the same type
         constraints and conversions as for simple assignment apply, taking the type of the scalar
         to be the unqualified version of its declared type.

    12   The rest of this subclause deals with initializers for objects that have aggregate or union
         type.

    13   The initializer for a structure or union object that has automatic storage duration shall be
         either an initializer list as described below, or a single expression that has compatible
         structure or union type. In the latter case, the initial value of the object, including
         unnamed members, is that of the expression.

    14   An array of character type may be initialized by a character string literal or UTF−8 string
         literal, optionally enclosed in braces. Successive bytes of the string literal (including the
         terminating null character if there is room or if the array is of unknown size) initialize the
         elements of the array.

    15   An array with element type compatible with a qualified or unqualified version of
         wchar_t, char16_t, or char32_t may be initialized by a wide string literal with
         the corresponding encoding prefix (L, u, or U, respectively), optionally enclosed in
         braces. Successive wide characters of the wide string literal (including the terminating
         null wide character if there is room or if the array is of unknown size) initialize the
         elements of the array.

    16   Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
         enclosed list of initializers for the elements or named members.

    17   Each brace-enclosed initializer list has an associated current object. When no
         designations are present, subobjects of the current object are initialized in order according
         to the type of the current object: array elements in increasing subscript order, structure
         members in declaration order, and the first named member of a union.[148] In contrast, a
         designation causes the following initializer to begin initialization of the subobject
         described by the designator. Initialization then continues forward in order, beginning
         with the next subobject after that described by the designator.[149]

    Footnote 148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
              subobjects are initialized as usual, but the subaggregate or contained union does not become the
              current object: current objects are associated only with brace-enclosed initializer lists.

    Footnote 149) After a union member is initialized, the next object is not the next member of the union; instead, it is
              the next subobject of an object containing the union.

    18   Each designator list begins its description with the current object associated with the
         closest surrounding brace pair. Each item in the designator list (in order) specifies a
         particular member of its current object and changes the current object for the next
         designator (if any) to be that member.[150] The current object that results at the end of the
         designator list is the subobject to be initialized by the following initializer.

    Footnote 150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
              the surrounding brace pair. Note, too, that each separate designator list is independent.

    19   The initialization shall occur in initializer list order, each initializer provided for a
         particular subobject overriding any previously listed initializer for the same subobject;[151]
         all subobjects that are not initialized explicitly shall be initialized implicitly the same as
         objects that have static storage duration.

    Footnote 151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
              not be evaluated at all.

    20   If the aggregate or union contains elements or members that are aggregates or unions,
         these rules apply recursively to the subaggregates or contained unions. If the initializer of
         a subaggregate or contained union begins with a left brace, the initializers enclosed by
         that brace and its matching right brace initialize the elements or members of the
         subaggregate or the contained union. Otherwise, only enough initializers from the list are
         taken to account for the elements or members of the subaggregate or the first member of
         the contained union; any remaining initializers are left to initialize the next element or
         member of the aggregate of which the current subaggregate or contained union is a part.

    21   If there are fewer initializers in a brace-enclosed list than there are elements or members
         of an aggregate, or fewer characters in a string literal used to initialize an array of known
         size than there are elements in the array, the remainder of the aggregate shall be
         initialized implicitly the same as objects that have static storage duration.

    22   If an array of unknown size is initialized, its size is determined by the largest indexed
         element with an explicit initializer. The array type is completed at the end of its
         initializer list.

    23   The evaluations of the initialization list expressions are indeterminately sequenced with
         respect to one another and thus the order in which any side effects occur is
         unspecified.[152]

    Footnote 152) In particular, the evaluation order need not be the same as the order of subobject initialization.

    24   EXAMPLE 1        Provided that <complex.h> has been #included, the declarations
                  int i = 3.5;
                  double complex c = 5 + 3 * I;
         define and initialize i with the value 3 and c with the value 5. 0 + i3. 0.

    25   EXAMPLE 2        The declaration
                  int x[] = { 1, 3, 5 };
         defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
         and there are three initializers.

    26   EXAMPLE 3        The declaration
                  int y[4][3] = {
                        { 1, 3, 5 },
                        { 2, 4, 6 },
                        { 3, 5, 7 },
                  };
         is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
         y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
         y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
         been achieved by
                  int y[4][3] = {
                        1, 3, 5, 2, 4, 6, 3, 5, 7
                  };
         The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
         next three are taken successively for y[1] and y[2].

    27   EXAMPLE 4        The declaration
                  int z[4][3] = {
                        { 1 }, { 2 }, { 3 }, { 4 }
                  };
         initializes the first column of z as specified and initializes the rest with zeros.

    28   EXAMPLE 5        The declaration
                  struct { int a[3], b; } w[] = { { 1 }, 2 };
         is a definition with an inconsistently bracketed initialization. It defines an array with two element
         structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.

    29   EXAMPLE 6         The declaration
                   short q[4][3][2] = {
                         { 1 },
                         { 2, 3 },
                         { 4, 5, 6 }
                   };
         contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
         object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
         q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
         q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
         only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
         for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
         respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
         diagnostic message would have been issued. The same initialization result could have been achieved by:
                   short q[4][3][2] = {
                         1, 0, 0, 0, 0, 0,
                         2, 3, 0, 0, 0, 0,
                         4, 5, 6
                   };
         or by:
                   short q[4][3][2] = {
                         {
                               { 1 },
                         },
                         {
                               { 2, 3 },
                         },
                         {
                               { 4, 5 },
                               { 6 },
                         }
                   };
         in a fully bracketed form.

    30   Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
         cause confusion.

    31   EXAMPLE 7         One form of initialization that completes array types involves typedef names. Given the
         declaration
                   typedef int A[];          // OK - declared with block scope
         the declaration
                   A a = { 1, 2 }, b = { 3, 4, 5 };
         is identical to
                   int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
         due to the rules for incomplete types.

    32   EXAMPLE 8       The declaration
                  char s[] = "abc", t[3] = "abc";
         defines ‘‘plain’’ char array objects s and t whose elements are initialized with character string literals.
         This declaration is identical to
                  char s[] = { 'a', 'b', 'c', '\0' },
                       t[] = { 'a', 'b', 'c' };
         The contents of the arrays are modifiable. On the other hand, the declaration
                  char *p = "abc";
         defines p with type ‘‘pointer to char’’ and initializes it to point to an object with type ‘‘array of char’’
         with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
         modify the contents of the array, the behavior is undefined.

    33   EXAMPLE 9       Arrays can be initialized to correspond to the elements of an enumeration by using
         designators:
                  enum { member_one, member_two };
                  const char *nm[] = {
                        [member_two] = "member two",
                        [member_one] = "member one",
                  };

    34   EXAMPLE 10       Structure members can be initialized to nonzero values without depending on their order:
                  div_t answer = { .quot = 2, .rem = -1 };

    35   EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
         might be misunderstood:
                  struct { int a[3], b; } w[] =
                        { [0].a = {1}, [1].a[0] = 2 };

    36   EXAMPLE 12       Space can be ‘‘allocated’’ from both ends of an array by using a single designator:
                  int a[MAX] = {
                        1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
                  };

    37   In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
         than ten, some of the values provided by the first five initializers will be overridden by the second five.

    38   EXAMPLE 13       Any member of a union can be initialized:
                  union { /* ... */ } u = { .any_member = 42 };

         Forward references: common definitions <stddef.h> (7.19).

### 6.7.10 [Static assertions]

    1 Syntax
                static_assert-declaration:
                         _Static_assert ( constant-expression , string-literal ) ;
        Constraints

    2   The constant expression shall compare unequal to 0.
        Semantics

    3   The constant expression shall be an integer constant expression. If the value of the
        constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
        constraint is violated and the implementation shall produce a diagnostic message that
        includes the text of the string literal, except that characters not in the basic source
        character set are not required to appear in the message.
        Forward references: diagnostics (7.2).

### 6.8 [Statements and blocks]

    1 Syntax
                statement:
                        labeled-statement
                        compound-statement
                        expression-statement
                        selection-statement
                        iteration-statement
                        jump-statement
        Semantics

    2   A statement specifies an action to be performed. Except as indicated, statements are
        executed in sequence.

    3   A block allows a set of declarations and statements to be grouped into one syntactic unit.
        The initializers of objects that have automatic storage duration, and the variable length
        array declarators of ordinary identifiers with block scope, are evaluated and the values are
        stored in the objects (including storing an indeterminate value in objects without an
        initializer) each time the declaration is reached in the order of execution, as if it were a
        statement, and within each declaration in the order that declarators appear.

    4   A full expression is an expression that is not part of another expression or of a declarator.
        Each of the following is a full expression: an initializer that is not part of a compound
        literal; the expression in an expression statement; the controlling expression of a selection
        statement (if or switch); the controlling expression of a while or do statement; each
        of the (optional) expressions of a for statement; the (optional) expression in a return
        statement. There is a sequence point between the evaluation of a full expression and the
        evaluation of the next full expression to be evaluated.
        Forward references: expression and null statements (6.8.3), selection statements
        (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).

### 6.8.1 [Labeled statements]

    1 Syntax
                labeled-statement:
                        identifier : statement
                        case constant-expression : statement
                        default : statement
        Constraints

    2   A case or default label shall appear only in a switch statement. Further
        constraints on such labels are discussed under the switch statement.

    3   Label names shall be unique within a function.
        Semantics

    4   Any statement may be preceded by a prefix that declares an identifier as a label name.
        Labels in themselves do not alter the flow of control, which continues unimpeded across
        them.
        Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).

### 6.8.2 [Compound statement]

    1 Syntax
                compound-statement:
                       { block-item-listopt }
                 block-item-list:
                         block-item
                         block-item-list block-item
                 block-item:
                         declaration
                         statement
        Semantics

    2   A compound statement is a block.

### 6.8.3 [Expression and null statements]

    1 Syntax
                expression-statement:
                        expressionopt ;
        Semantics

    2   The expression in an expression statement is evaluated as a void expression for its side
        effects.[153]

    Footnote 153) Such as assignments, and function calls which have side effects.

    3   A null statement (consisting of just a semicolon) performs no operations.

    4   EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
        discarding of its value may be made explicit by converting the expression to a void expression by means of
        a cast:
                 int p(int);
                 /* ... */
                 (void)p(0);

    5   EXAMPLE 2       In the program fragment
                 char *s;
                 /* ... */
                 while (*s++ != '\0')
                         ;
        a null statement is used to supply an empty loop body to the iteration statement.

    6   EXAMPLE 3       A null statement may also be used to carry a label just before the closing } of a compound
        statement.
                 while (loop1) {
                       /* ... */
                       while (loop2) {
                               /* ... */
                               if (want_out)
                                       goto end_loop1;
                               /* ... */
                       }
                       /* ... */
                 end_loop1: ;
                 }

        Forward references: iteration statements (6.8.5).

### 6.8.4 [Selection statements]

    1 Syntax
                selection-statement:
                         if ( expression ) statement
                         if ( expression ) statement else statement
                         switch ( expression ) statement
        Semantics

    2   A selection statement selects among a set of statements depending on the value of a
        controlling expression.

    3   A selection statement is a block whose scope is a strict subset of the scope of its
        enclosing block. Each associated substatement is also a block whose scope is a strict
        subset of the scope of the selection statement.

### 6.8.4.1 [The if statement]

    1 Constraints
       The controlling expression of an if statement shall have scalar type.
        Semantics

    2   In both forms, the first substatement is executed if the expression compares unequal to 0.
        In the else form, the second substatement is executed if the expression compares equal
        to 0. If the first substatement is reached via a label, the second substatement is not
        executed.

    3   An else is associated with the lexically nearest preceding if that is allowed by the
        syntax.

### 6.8.4.2 [The switch statement]

    1 Constraints
       The controlling expression of a switch statement shall have integer type.

    2   If a switch statement has an associated case or default label within the scope of an
        identifier with a variably modified type, the entire switch statement shall be within the
        scope of that identifier.[154]

    Footnote 154) That is, the declaration either precedes the switch statement, or it follows the last case or
             default label associated with the switch that is in the block containing the declaration.

    3   The expression of each case label shall be an integer constant expression and no two of
        the case constant expressions in the same switch statement shall have the same value
        after conversion. There may be at most one default label in a switch statement.
        (Any enclosed switch statement may have a default label or case constant
        expressions with values that duplicate case constant expressions in the enclosing
        switch statement.)
        Semantics

    4   A switch statement causes control to jump to, into, or past the statement that is the
        switch body, depending on the value of a controlling expression, and on the presence of a
        default label and the values of any case labels on or in the switch body. A case or
        default label is accessible only within the closest enclosing switch statement.

    5   The integer promotions are performed on the controlling expression. The constant
        expression in each case label is converted to the promoted type of the controlling
        expression. If a converted value matches that of the promoted controlling expression,
        control jumps to the statement following the matched case label. Otherwise, if there is
        a default label, control jumps to the labeled statement. If no converted case constant
        expression matches and there is no default label, no part of the switch body is
        executed.
        Implementation limits

    6   As discussed in 5.2.4.1, the implementation may limit the number of case values in a
        switch statement.

    7   EXAMPLE        In the artificial program fragment
                 switch (expr)
                 {
                       int i = 4;
                       f(i);
                 case 0:
                       i = 17;
                       /* falls through into default code */
                 default:
                       printf("%d\n", i);
                 }
        the object whose identifier is i exists with automatic storage duration (within the block) but is never
        initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
        access an indeterminate value. Similarly, the call to the function f cannot be reached.

### 6.8.5 [Iteration statements]

    1 Syntax
                iteration-statement:
                         while ( expression ) statement
                         do statement while ( expression ) ;
                         for ( expressionopt ; expressionopt ; expressionopt ) statement
                         for ( declaration expressionopt ; expressionopt ) statement
        Constraints

    2   The controlling expression of an iteration statement shall have scalar type.

    3   The declaration part of a for statement shall only declare identifiers for objects having
        storage class auto or register.
        Semantics

    4   An iteration statement causes a statement called the loop body to be executed repeatedly
        until the controlling expression compares equal to 0. The repetition occurs regardless of
        whether the loop body is entered from the iteration statement or by a jump.[155]

    Footnote 155) Code jumped over is not executed. In particular, the controlling expression of a for or while
             statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.

    5   An iteration statement is a block whose scope is a strict subset of the scope of its
        enclosing block. The loop body is also a block whose scope is a strict subset of the scope
        of the iteration statement.

    6   An iteration statement whose controlling expression is not a constant expression,[156] that
        performs no input/output operations, does not access volatile objects, and performs no
        synchronization or atomic operations in its body, controlling expression, or (in the case of
        a for statement) its expression-3, may be assumed by the implementation to
        terminate.[157]

    Footnote 156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression.

    Footnote 157) This is intended to allow compiler transformations such as removal of empty loops even when
             termination cannot be proven.

### 6.8.5.1 [The while statement]

    1   The evaluation of the controlling expression takes place before each execution of the loop
        body.

### 6.8.5.2 [The do statement]

    1   The evaluation of the controlling expression takes place after each execution of the loop
        body.

### 6.8.5.3 [The for statement]

    1   The statement
                 for ( clause-1 ; expression-2 ; expression-3 ) statement
        behaves as follows: The expression expression-2 is the controlling expression that is
        evaluated before each execution of the loop body. The expression expression-3 is
        evaluated as a void expression after each execution of the loop body. If clause-1 is a
        declaration, the scope of any identifiers it declares is the remainder of the declaration and
        the entire loop, including the other two expressions; it is reached in the order of execution
        before the first evaluation of the controlling expression. If clause-1 is an expression, it is
        evaluated as a void expression before the first evaluation of the controlling expression.[158]

    Footnote 158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
             the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
             such that execution of the loop continues until the expression compares equal to 0; and expression-3
             specifies an operation (such as incrementing) that is performed after each iteration.

    2   Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
        nonzero constant.

### 6.8.6 [Jump statements]

    1 Syntax
                jump-statement:
                        goto identifier ;
                        continue ;
                        break ;
                        return expressionopt ;
        Semantics

    2   A jump statement causes an unconditional jump to another place.

### 6.8.6.1 [The goto statement]

    1 Constraints
       The identifier in a goto statement shall name a label located somewhere in the enclosing
        function. A goto statement shall not jump from outside the scope of an identifier having
        a variably modified type to inside the scope of that identifier.
        Semantics

    2   A goto statement causes an unconditional jump to the statement prefixed by the named
        label in the enclosing function.

    3   EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
        following outline presents one possible approach to a problem based on these three assumptions:
          1.   The general initialization code accesses objects only visible to the current function.
          2.   The general initialization code is too large to warrant duplication.
          3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
             continue statements, for example.)
                /* ... */
                goto first_time;
                for (;;) {
                        // determine next operation
                        /* ... */
                        if (need to reinitialize) {
                                // reinitialize-only code
                                /* ... */
                        first_time:
                                // general initialization code
                                /* ... */
                                continue;
                        }
                        // handle other operations
                        /* ... */
                }

    4   EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
        modified types. A jump within the scope, however, is permitted.
                goto lab3;                         // invalid: going INTO scope of VLA.
                {
                      double a[n];
                      a[j] = 4.4;
                lab3:
                      a[j] = 3.3;
                      goto lab4;                   // valid: going WITHIN scope of VLA.
                      a[j] = 5.5;
                lab4:
                      a[j] = 6.6;
                }
                goto lab4;                         // invalid: going INTO scope of VLA.

### 6.8.6.2 [The continue statement]

    1 Constraints
       A continue statement shall appear only in or as a loop body.
        Semantics

    2   A continue statement causes a jump to the loop-continuation portion of the smallest
        enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
        of the statements
        while (/* ... */) {                  do {                                 for (/* ... */) {
           /* ... */                            /* ... */                            /* ... */
           continue;                            continue;                            continue;
           /* ... */                            /* ... */                            /* ... */
        contin: ;                            contin: ;                            contin: ;
        }                                    } while (/* ... */);                 }
        unless the continue statement shown is in an enclosed iteration statement (in which
        case it is interpreted within that statement), it is equivalent to goto contin;.[159]

    Footnote 159) Following the contin: label is a null statement.

### 6.8.6.3 [The break statement]

    1 Constraints
       A break statement shall appear only in or as a switch body or loop body.
        Semantics

    2   A break statement terminates execution of the smallest enclosing switch or iteration
        statement.

### 6.8.6.4 [The return statement]

    1 Constraints
       A return statement with an expression shall not appear in a function whose return type
        is void. A return statement without an expression shall only appear in a function
        whose return type is void.
        Semantics

    2   A return statement terminates execution of the current function and returns control to
        its caller. A function may have any number of return statements.

    3   If a return statement with an expression is executed, the value of the expression is
        returned to the caller as the value of the function call expression. If the expression has a
        type different from the return type of the function in which it appears, the value is
        converted as if by assignment to an object having the return type of the function.[160]

    Footnote 160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
             apply to the case of function return. The representation of floating-point values may have wider range
             or precision than implied by the type; a cast may be used to remove this extra range and precision.

    4   EXAMPLE       In:
                struct s { double i; } f(void);
                union {
                      struct {
                            int f1;
                            struct s f2;
                      } u1;
                      struct {
                            struct s f3;
                            int f4;
                      } u2;
                } g;
                struct s f(void)
                {
                      return g.u1.f2;
                }
                /* ... */
                g.u2.f3 = f();
        there is no undefined behavior, although there would be if the assignment were done directly (without using
        a function call to fetch the value).

### 6.9 [External definitions]

    1 Syntax
                translation-unit:
                         external-declaration
                         translation-unit external-declaration
                 external-declaration:
                        function-definition
                        declaration
        Constraints

    2   The storage-class specifiers auto and register shall not appear in the declaration
        specifiers in an external declaration.

    3   There shall be no more than one external definition for each identifier declared with
        internal linkage in a translation unit. Moreover, if an identifier declared with internal
        linkage is used in an expression (other than as a part of the operand of a sizeof or
        _Alignof operator whose result is an integer constant), there shall be exactly one
        external definition for the identifier in the translation unit.
        Semantics

    4   As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
        which consists of a sequence of external declarations. These are described as ‘‘external’’
        because they appear outside any function (and hence have file scope). As discussed in
        6.7, a declaration that also causes storage to be reserved for an object or a function named
        by the identifier is a definition.

    5   An external definition is an external declaration that is also a definition of a function
        (other than an inline definition) or an object. If an identifier declared with external
        linkage is used in an expression (other than as part of the operand of a sizeof or
        _Alignof operator whose result is an integer constant), somewhere in the entire
        program there shall be exactly one external definition for the identifier; otherwise, there
        shall be no more than one.[161]

    Footnote 161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
             external definition for it.

### 6.9.1 [Function definitions]

    1 Syntax
                function-definition:
                        declaration-specifiers declarator declaration-listopt compound-statement
                 declaration-list:
                        declaration
                        declaration-list declaration
        Constraints

    2   The identifier declared in a function definition (which is the name of the function) shall
        have a function type, as specified by the declarator portion of the function definition.[162]

    Footnote 162) The intent is that the type category in a function definition cannot be inherited from a typedef:
                      typedef int F(void);                          // type F is ‘‘function with no parameters
                                                                    //                returning int’’
                      F f, g;                                       // f and g both have type compatible with F
                      F f { /* ... */ }                             // WRONG: syntax/constraint error
                      F g() { /* ... */ }                           // WRONG: declares that g returns a function
                      int f(void) { /* ... */ }                     // RIGHT: f has type compatible with F
                      int g() { /* ... */ }                         // RIGHT: g has type compatible with F
                      F *e(void) { /* ... */ }                      // e returns a pointer to a function
                      F *((e))(void) { /* ... */ }                  // same: parentheses irrelevant
                      int (*fp)(void);                              // fp points to a function that has type F
                      F *Fp;                                        // Fp points to a function that has type F

    3   The return type of a function shall be void or a complete object type other than array
        type.

    4   The storage-class specifier, if any, in the declaration specifiers shall be either extern or
        static.

    5   If the declarator includes a parameter type list, the declaration of each parameter shall
        include an identifier, except for the special case of a parameter list consisting of a single
        parameter of type void, in which case there shall not be an identifier. No declaration list
        shall follow.

    6   If the declarator includes an identifier list, each declaration in the declaration list shall
        have at least one declarator, those declarators shall declare only identifiers from the
        identifier list, and every identifier in the identifier list shall be declared. An identifier
        declared as a typedef name shall not be redeclared as a parameter. The declarations in the
        declaration list shall contain no storage-class specifier other than register and no
        initializations.
         Semantics

    7    The declarator in a function definition specifies the name of the function being defined
         and the identifiers of its parameters. If the declarator includes a parameter type list, the
         list also specifies the types of all the parameters; such a declarator also serves as a
         function prototype for later calls to the same function in the same translation unit. If the
         declarator includes an identifier list,[163] the types of the parameters shall be declared in a
         following declaration list. In either case, the type of each parameter is adjusted as
         described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
         type.

    Footnote 163) See ‘‘future language directions’’ (6.11.7).

    8    If a function that accepts a variable number of arguments is defined without a parameter
         type list that ends with the ellipsis notation, the behavior is undefined.

    9    Each parameter has automatic storage duration; its identifier is an lvalue.[164] The layout
         of the storage for parameters is unspecified.

    Footnote 164) A parameter identifier cannot be redeclared in the function body except in an enclosed block.

    10   On entry to the function, the size expressions of each variably modified parameter are
         evaluated and the value of each argument expression is converted to the type of the
         corresponding parameter as if by assignment. (Array expressions and function
         designators as arguments were converted to pointers before the call.)

    11   After all parameters have been assigned, the compound statement that constitutes the
         body of the function definition is executed.

    12   If the } that terminates a function is reached, and the value of the function call is used by
         the caller, the behavior is undefined.

    13   EXAMPLE 1       In the following:
                  extern int max(int a, int b)
                  {
                        return a > b ? a : b;
                  }
         extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
         function declarator; and
                  { return a > b ? a : b; }
         is the function body. The following similar definition uses the identifier-list form for the parameter
         declarations:
                  extern int max(a, b)
                  int a, b;
                  {
                        return a > b ? a : b;
                  }
         Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
         that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
         to the function, whereas the second form does not.

    14   EXAMPLE 2           To pass one function to another, one might say
                              int f(void);
                              /* ... */
                              g(f);
         Then the definition of g might read
                  void g(int (*funcp)(void))
                  {
                        /* ... */
                        (*funcp)(); /* or funcp(); ...                    */
                  }
         or, equivalently,
                  void g(int func(void))
                  {
                        /* ... */
                        func(); /* or (*func)(); ...                   */
                  }

### 6.9.2 [External object definitions]

    1 Semantics
        If the declaration of an identifier for an object has file scope and an initializer, the
         declaration is an external definition for the identifier.

    2    A declaration of an identifier for an object that has file scope without an initializer, and
         without a storage-class specifier or with the storage-class specifier static, constitutes a
         tentative definition. If a translation unit contains one or more tentative definitions for an
         identifier, and the translation unit contains no external definition for that identifier, then
         the behavior is exactly as if the translation unit contains a file scope declaration of that
         identifier, with the composite type as of the end of the translation unit, with an initializer
         equal to 0.

    3    If the declaration of an identifier for an object is a tentative definition and has internal
         linkage, the declared type shall not be an incomplete type.

    4   EXAMPLE 1
                 int i1 = 1;                    // definition, external linkage
                 static int i2 = 2;             // definition, internal linkage
                 extern int i3 = 3;             // definition, external linkage
                 int i4;                        // tentative definition, external linkage
                 static int i5;                 // tentative definition, internal linkage
                 int i1;                        // valid tentative definition, refers to previous
                 int i2;                        // 6.2.2 renders undefined, linkage disagreement
                 int i3;                        // valid tentative definition, refers to previous
                 int i4;                        // valid tentative definition, refers to previous
                 int i5;                        // 6.2.2 renders undefined, linkage disagreement
                 extern int i1;                 // refers to previous, whose linkage is external
                 extern int i2;                 // refers to previous, whose linkage is internal
                 extern int i3;                 // refers to previous, whose linkage is external
                 extern int i4;                 // refers to previous, whose linkage is external
                 extern int i5;                 // refers to previous, whose linkage is internal

    5   EXAMPLE 2       If at the end of the translation unit containing
                 int i[];
        the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
        zero on program startup.

### 6.10 [Preprocessing directives]

    1 Syntax
                preprocessing-file:
                        groupopt
                 group:
                          group-part
                          group group-part
                 group-part:
                        if-section
                        control-line
                        text-line
                        # non-directive
                 if-section:
                          if-group elif-groupsopt else-groupopt endif-line
                 if-group:
                         # if     constant-expression new-line groupopt
                         # ifdef identifier new-line groupopt
                         # ifndef identifier new-line groupopt
                 elif-groups:
                         elif-group
                         elif-groups elif-group
                 elif-group:
                         # elif        constant-expression new-line groupopt
                 else-group:
                         # else        new-line groupopt
                 endif-line:
                         # endif       new-line
                 control-line:
                        # include pp-tokens new-line
                        # define identifier replacement-list new-line
                        # define identifier lparen identifier-listopt )
                                                        replacement-list new-line
                        # define identifier lparen ... ) replacement-list new-line
                        # define identifier lparen identifier-list , ... )
                                                        replacement-list new-line
                        # undef   identifier new-line
                        # line    pp-tokens new-line
                        # error   pp-tokensopt new-line
                        # pragma pp-tokensopt new-line
                        #         new-line
                 text-line:
                         pp-tokensopt new-line
                 non-directive:
                        pp-tokens new-line
                 lparen:
                           a ( character not immediately preceded by white-space
                 replacement-list:
                        pp-tokensopt
                 pp-tokens:
                        preprocessing-token
                        pp-tokens preprocessing-token
                 new-line:
                        the new-line character
        Description

    2   A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
        following constraints: The first token in the sequence is a # preprocessing token that (at
        the start of translation phase 4) is either the first character in the source file (optionally
        after white space containing no new-line characters) or that follows white space
        containing at least one new-line character. The last token in the sequence is the first new-
        line character that follows the first token in the sequence.[165] A new-line character ends
        the preprocessing directive even if it occurs within what would otherwise be an
        invocation of a function-like macro.

    Footnote 165) Thus, preprocessing directives are commonly called ‘‘lines’’. These ‘‘lines’’ have no other syntactic
             significance, as all white space is equivalent except in certain situations during preprocessing (see the
             # character string literal creation operator in 6.10.3.2, for example).

    3   A text line shall not begin with a # preprocessing token. A non-directive shall not begin
        with any of the directive names appearing in the syntax.

    4   When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
        sequence of preprocessing tokens to occur between the directive name and the following
        new-line character.
        Constraints

    5   The only white-space characters that shall appear between preprocessing tokens within a
        preprocessing directive (from just after the introducing # preprocessing token through
        just before the terminating new-line character) are space and horizontal-tab (including
        spaces that have replaced comments or possibly other white-space characters in
        translation phase 3).
        Semantics

    6   The implementation can process and skip sections of source files conditionally, include
        other source files, and replace macros. These capabilities are called preprocessing,
        because conceptually they occur before translation of the resulting translation unit.

    7   The preprocessing tokens within a preprocessing directive are not subject to macro
        expansion unless otherwise stated.

    8   EXAMPLE        In:
                 #define EMPTY
                 EMPTY # include <file.h>
        the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
        begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
        replaced.

### 6.10.1 [Conditional inclusion]

    1 Constraints
       The expression that controls conditional inclusion shall be an integer constant expression
        except that: identifiers (including those lexically identical to keywords) are interpreted as
        described below;[166] and it may contain unary operator expressions of the form
             defined identifier
        or
             defined ( identifier )
        which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is
        predefined or if it has been the subject of a #define preprocessing directive without an
        intervening #undef directive with the same subject identifier), 0 if it is not.

    Footnote 166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
             either are or are not macro names — there simply are no keywords, enumeration constants, etc.

    2   Each preprocessing token that remains (in the list of preprocessing tokens that will
        become the controlling expression) after all macro replacements have occurred shall be in
        the lexical form of a token (6.4).
        Semantics

    3   Preprocessing directives of the forms
           # if   constant-expression new-line groupopt
           # elif constant-expression new-line groupopt
        check whether the controlling constant expression evaluates to nonzero.

    4   Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
        the controlling constant expression are replaced (except for those macro names modified
        by the defined unary operator), just as in normal text. If the token defined is
        generated as a result of this replacement process or use of the defined unary operator
        does not match one of the two specified forms prior to macro replacement, the behavior is
        undefined. After all replacements due to macro expansion and the defined unary
        operator have been performed, all remaining identifiers (including those lexically
        identical to keywords) are replaced with the pp-number 0, and then each preprocessing
        token is converted into a token. The resulting tokens compose the controlling constant
        expression which is evaluated according to the rules of 6.6. For the purposes of this
        token conversion and evaluation, all signed integer types and all unsigned integer types
        act as if they have the same representation as, respectively, the types intmax_t and
        uintmax_t defined in the header <stdint.h>.[167] This includes interpreting
        character constants, which may involve converting escape sequences into execution
        character set members. Whether the numeric value for these character constants matches
        the value obtained when an identical character constant occurs in an expression (other
        than within a #if or #elif directive) is implementation-defined.[168] Also, whether a
        single-character character constant may have a negative value is implementation-defined.

    Footnote 167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
             0x8000 is signed and positive within a #if expression even though it would be unsigned in
             translation phase 7.

    Footnote 168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
             evaluate to the same value in these two contexts.
               #if 'z' - 'a' == 25
               if ('z' - 'a' == 25)

    5   Preprocessing directives of the forms
           # ifdef identifier new-line groupopt
           # ifndef identifier new-line groupopt
        check whether the identifier is or is not currently defined as a macro name. Their
        conditions are equivalent to #if defined identifier and #if !defined identifier
        respectively.

    6   Each directive’s condition is checked in order. If it evaluates to false (zero), the group
        that it controls is skipped: directives are processed only through the name that determines
        the directive in order to keep track of the level of nested conditionals; the rest of the
        directives’ preprocessing tokens are ignored, as are the other preprocessing tokens in the
        group. Only the first group whose control condition evaluates to true (nonzero) is
        processed. If none of the conditions evaluates to true, and there is a #else directive, the
        group controlled by the #else is processed; lacking a #else directive, all the groups
        until the #endif are skipped.[169]
        Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
        integer types (7.20.1.5).

    Footnote 169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
             before the terminating new-line character. However, comments may appear anywhere in a source file,
             including within a preprocessing directive.

### 6.10.2 [Source file inclusion]

    1 Constraints
       A #include directive shall identify a header or source file that can be processed by the
        implementation.
        Semantics

    2   A preprocessing directive of the form
           # include <h-char-sequence> new-line
        searches a sequence of implementation-defined places for a header identified uniquely by
        the specified sequence between the < and > delimiters, and causes the replacement of that
        directive by the entire contents of the header. How the places are specified or the header
        identified is implementation-defined.

    3   A preprocessing directive of the form
           # include "q-char-sequence" new-line
        causes the replacement of that directive by the entire contents of the source file identified
        by the specified sequence between the " delimiters. The named source file is searched
        for in an implementation-defined manner. If this search is not supported, or if the search
        fails, the directive is reprocessed as if it read
           # include <h-char-sequence> new-line
        with the identical contained sequence (including > characters, if any) from the original
        directive.

    4   A preprocessing directive of the form
           # include pp-tokens new-line
        (that does not match one of the two previous forms) is permitted. The preprocessing
        tokens after include in the directive are processed just as in normal text. (Each
        identifier currently defined as a macro name is replaced by its replacement list of
        preprocessing tokens.) The directive resulting after all replacements shall match one of
        the two previous forms.[170] The method by which a sequence of preprocessing tokens
        between a < and a > preprocessing token pair or a pair of " characters is combined into a
        single header name preprocessing token is implementation-defined.

    Footnote 170) Note that adjacent string literals are not concatenated into a single string literal (see the translation
             phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.

    5   The implementation shall provide unique mappings for sequences consisting of one or
        more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
        first character shall not be a digit. The implementation may ignore distinctions of
        alphabetical case and restrict the mapping to eight significant characters before the
        period.

    6   A #include preprocessing directive may appear in a source file that has been read
        because of a #include directive in another file, up to an implementation-defined
        nesting limit (see 5.2.4.1).

    7   EXAMPLE 1       The most common uses of #include preprocessing directives are as in the following:
                 #include <stdio.h>
                 #include "myprog.h"

    8   EXAMPLE 2     This illustrates macro-replaced #include directives:
               #if VERSION == 1
                     #define INCFILE            "vers1.h"
               #elif VERSION == 2
                     #define INCFILE            "vers2.h"        // and so on
               #else
                      #define INCFILE           "versN.h"
               #endif
               #include INCFILE

        Forward references: macro replacement (6.10.3).

### 6.10.3 [Macro replacement]

    1 Constraints
       Two replacement lists are identical if and only if the preprocessing tokens in both have
        the same number, ordering, spelling, and white-space separation, where all white-space
        separations are considered identical.

    2   An identifier currently defined as an object-like macro shall not be redefined by another
        #define preprocessing directive unless the second definition is an object-like macro
        definition and the two replacement lists are identical. Likewise, an identifier currently
        defined as a function-like macro shall not be redefined by another #define
        preprocessing directive unless the second definition is a function-like macro definition
        that has the same number and spelling of parameters, and the two replacement lists are
        identical.

    3   There shall be white-space between the identifier and the replacement list in the definition
        of an object-like macro.

    4   If the identifier-list in the macro definition does not end with an ellipsis, the number of
        arguments (including those arguments consisting of no preprocessing tokens) in an
        invocation of a function-like macro shall equal the number of parameters in the macro
        definition. Otherwise, there shall be more arguments in the invocation than there are
        parameters in the macro definition (excluding the ...). There shall exist a )
        preprocessing token that terminates the invocation.

    5   The identifier _ _VA_ARGS_ _ shall occur only in the replacement-list of a function-like
        macro that uses the ellipsis notation in the parameters.

    6   A parameter identifier in a function-like macro shall be uniquely declared within its
        scope.
        Semantics

    7   The identifier immediately following the define is called the macro name. There is one
        name space for macro names. Any white-space characters preceding or following the
        replacement list of preprocessing tokens are not considered part of the replacement list
         for either form of macro.

    8    If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
         a preprocessing directive could begin, the identifier is not subject to macro replacement.

    9    A preprocessing directive of the form
            # define identifier replacement-list new-line
         defines an object-like macro that causes each subsequent instance of the macro name[171]
         to be replaced by the replacement list of preprocessing tokens that constitute the
         remainder of the directive. The replacement list is then rescanned for more macro names
         as specified below.

    Footnote 171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
              not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
              are never scanned for macro names or parameters.

    10   A preprocessing directive of the form
            # define identifier lparen identifier-listopt ) replacement-list new-line
            # define identifier lparen ... ) replacement-list new-line
            # define identifier lparen identifier-list , ... ) replacement-list new-line
         defines a function-like macro with parameters, whose use is similar syntactically to a
         function call. The parameters are specified by the optional list of identifiers, whose scope
         extends from their declaration in the identifier list until the new-line character that
         terminates the #define preprocessing directive. Each subsequent instance of the
         function-like macro name followed by a ( as the next preprocessing token introduces the
         sequence of preprocessing tokens that is replaced by the replacement list in the definition
         (an invocation of the macro). The replaced sequence of preprocessing tokens is
         terminated by the matching ) preprocessing token, skipping intervening matched pairs of
         left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
         tokens making up an invocation of a function-like macro, new-line is considered a normal
         white-space character.

    11   The sequence of preprocessing tokens bounded by the outside-most matching parentheses
         forms the list of arguments for the function-like macro. The individual arguments within
         the list are separated by comma preprocessing tokens, but comma preprocessing tokens
         between matching inner parentheses do not separate arguments. If there are sequences of
         preprocessing tokens within the list of arguments that would otherwise act as
         preprocessing directives,[172] the behavior is undefined.

    Footnote 172) Despite the name, a non-directive is a preprocessing directive.

    12   If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
         including any separating comma preprocessing tokens, are merged to form a single item:
        the variable arguments. The number of arguments so combined is such that, following
        merger, the number of arguments is one more than the number of parameters in the macro
        definition (excluding the ...).

### 6.10.3.1 [Argument substitution]

    1   After the arguments for the invocation of a function-like macro have been identified,
        argument substitution takes place. A parameter in the replacement list, unless preceded
        by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
        replaced by the corresponding argument after all macros contained therein have been
        expanded. Before being substituted, each argument’s preprocessing tokens are
        completely macro replaced as if they formed the rest of the preprocessing file; no other
        preprocessing tokens are available.

    2   An identifier _ _VA_ARGS_ _ that occurs in the replacement list shall be treated as if it
        were a parameter, and the variable arguments shall form the preprocessing tokens used to
        replace it.

### 6.10.3.2 [The # operator]

    1 Constraints
       Each # preprocessing token in the replacement list for a function-like macro shall be
        followed by a parameter as the next preprocessing token in the replacement list.
        Semantics

    2   If, in the replacement list, a parameter is immediately preceded by a # preprocessing
        token, both are replaced by a single character string literal preprocessing token that
        contains the spelling of the preprocessing token sequence for the corresponding
        argument. Each occurrence of white space between the argument’s preprocessing tokens
        becomes a single space character in the character string literal. White space before the
        first preprocessing token and after the last preprocessing token composing the argument
        is deleted. Otherwise, the original spelling of each preprocessing token in the argument
        is retained in the character string literal, except for special handling for producing the
        spelling of string literals and character constants: a \ character is inserted before each "
        and \ character of a character constant or string literal (including the delimiting "
        characters), except that it is implementation-defined whether a \ character is inserted
        before the \ character beginning a universal character name. If the replacement that
        results is not a valid character string literal, the behavior is undefined. The character
        string literal corresponding to an empty argument is "". The order of evaluation of # and
        ## operators is unspecified.

### 6.10.3.3 [The ## operator]

    1 Constraints
       A ## preprocessing token shall not occur at the beginning or at the end of a replacement
        list for either form of macro definition.
        Semantics

    2   If, in the replacement list of a function-like macro, a parameter is immediately preceded
        or followed by a ## preprocessing token, the parameter is replaced by the corresponding
        argument’s preprocessing token sequence; however, if an argument consists of no
        preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
        instead.[173]

    Footnote 173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
             exist only within translation phase 4.

    3   For both object-like and function-like macro invocations, before the replacement list is
        reexamined for more macro names to replace, each instance of a ## preprocessing token
        in the replacement list (not from an argument) is deleted and the preceding preprocessing
        token is concatenated with the following preprocessing token. Placemarker
        preprocessing tokens are handled specially: concatenation of two placemarkers results in
        a single placemarker preprocessing token, and concatenation of a placemarker with a
        non-placemarker preprocessing token results in the non-placemarker preprocessing token.
        If the result is not a valid preprocessing token, the behavior is undefined. The resulting
        token is available for further macro replacement. The order of evaluation of ## operators
        is unspecified.

    4   EXAMPLE       In the following fragment:
                #define hash_hash # ## #
                #define mkstr(a) # a
                #define in_between(a) mkstr(a)
                #define join(c, d) in_between(c hash_hash d)
                char p[] = join(x, y); // equivalent to
                                       // char p[] = "x ## y";
        The expansion produces, at various stages:
                join(x, y)
                in_between(x hash_hash y)
                in_between(x ## y)
                mkstr(x ## y)
                "x ## y"
        In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
        this new token is not the ## operator.

### 6.10.3.4 [Rescanning and further replacement]

    1   After all parameters in the replacement list have been substituted and # and ##
        processing has taken place, all placemarker preprocessing tokens are removed. The
        resulting preprocessing token sequence is then rescanned, along with all subsequent
        preprocessing tokens of the source file, for more macro names to replace.

    2   If the name of the macro being replaced is found during this scan of the replacement list
        (not including the rest of the source file’s preprocessing tokens), it is not replaced.
        Furthermore, if any nested replacements encounter the name of the macro being replaced,
        it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
        available for further replacement even if they are later (re)examined in contexts in which
        that macro name preprocessing token would otherwise have been replaced.

    3   The resulting completely macro-replaced preprocessing token sequence is not processed
        as a preprocessing directive even if it resembles one, but all pragma unary operator
        expressions within it are then processed as specified in 6.10.9 below.

    4   EXAMPLE There are cases where it is not clear whether a replacement is nested or not. For example,
        given the following macro definitions:
                #define f(a) a*g
                #define g(a) f(a)
        the invocation
                f(2)(9)
        may expand to either
                2*f(9)
        or
                2*9*g
        Strictly conforming programs are not permitted to depend on such unspecified behavior.

### 6.10.3.5 [Scope of macro definitions]

    1   A macro definition lasts (independent of block structure) until a corresponding #undef
        directive is encountered or (if none is encountered) until the end of the preprocessing
        translation unit. Macro definitions have no significance after translation phase 4.

    2   A preprocessing directive of the form
             # undef identifier new-line
        causes the specified identifier no longer to be defined as a macro name. It is ignored if
        the specified identifier is not currently defined as a macro name.

    3   EXAMPLE 1        The simplest use of this facility is to define a ‘‘manifest constant’’, as in
                #define TABSIZE 100
                 int table[TABSIZE];

    4   EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
        It has the advantages of working for any compatible types of the arguments and of generating in-line code
        without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
        arguments a second time (including side effects) and generating more code than a function if invoked
        several times. It also cannot have its address taken, as it has none.
                 #define max(a, b) ((a) > (b) ? (a) : (b))
        The parentheses ensure that the arguments and the resulting expression are bound properly.

    5   EXAMPLE 3      To illustrate the rules for redefinition and reexamination, the sequence
                 #define x      3
                 #define f(a)   f(x * (a))
                 #undef x
                 #define x      2
                 #define g      f
                 #define z      z[0]
                 #define h      g(~
                 #define m(a)   a(w)
                 #define w      0,1
                 #define t(a)   a
                 #define p()    int
                 #define q(x)   x
                 #define r(x,y) x ## y
                 #define str(x) # x
                 f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
                 g(x+(3,4)-w) | h 5) & m
                       (f)^m(m);
                 p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
                 char c[2][6] = { str(hello), str() };
        results in
                 f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
                 f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
                 int i[] = { 1, 23, 4, 5, };
                 char c[2][6] = { "hello", "" };

    6   EXAMPLE 4      To illustrate the rules for creating character string literals and concatenating tokens, the
        sequence
                 #define str(s)      # s
                 #define xstr(s)     str(s)
                 #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
                                         x ## s, x ## t)
                 #define INCFILE(n) vers ## n
                 #define glue(a, b) a ## b
                 #define xglue(a, b) glue(a, b)
                 #define HIGHLOW     "hello"
                 #define LOW         LOW ", world"
                 debug(1, 2);
                 fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
                       == 0) str(: @\n), s);
                 #include xstr(INCFILE(2).h)
                 glue(HIGH, LOW);
                 xglue(HIGH, LOW)
        results in
                 printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
                 fputs(
                   "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
                   s);
                 #include "vers2.h"    (after macro replacement, before file access)
                 "hello";
                 "hello" ", world"
        or, after concatenation of the character string literals,
                 printf("x1= %d, x2= %s", x1, x2);
                 fputs(
                   "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
                   s);
                 #include "vers2.h"    (after macro replacement, before file access)
                 "hello";
                 "hello, world"
        Space around the # and ## tokens in the macro definition is optional.

    7   EXAMPLE 5        To illustrate the rules for placemarker preprocessing tokens, the sequence
                 #define t(x,y,z) x ## y ## z
                 int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
                            t(10,,), t(,11,), t(,,12), t(,,) };
        results in
                 int j[] = { 123, 45, 67, 89,
                             10, 11, 12, };

    8   EXAMPLE 6        To demonstrate the redefinition rules, the following sequence is valid.
                 #define OBJ_LIKE      (1-1)
                 #define OBJ_LIKE      /* white space */ (1-1) /* other */
                 #define FUNC_LIKE(a)   ( a )
                 #define FUNC_LIKE( a )( /* note the white space */ \
                                         a /* other stuff on this line
                                             */ )
        But the following redefinitions are invalid:
                 #define OBJ_LIKE    (0)     // different token sequence
                 #define OBJ_LIKE    (1 - 1) // different white space
                 #define FUNC_LIKE(b) ( a ) // different parameter usage
                 #define FUNC_LIKE(b) ( b ) // different parameter spelling

    9   EXAMPLE 7        Finally, to show the variable argument list macro facilities:
                 #define debug(...)       fprintf(stderr, _ _VA_ARGS_ _)
                 #define showlist(...)    puts(#_ _VA_ARGS_ _)
                 #define report(test, ...) ((test)?puts(#test):\
                             printf(_ _VA_ARGS_ _))
                 debug("Flag");
                 debug("X = %d\n", x);
                 showlist(The first, second, and third items.);
                 report(x>y, "x is %d but y is %d", x, y);
        results in
                 fprintf(stderr, "Flag" );
                 fprintf(stderr, "X = %d\n", x );
                 puts( "The first, second, and third items." );
                 ((x>y)?puts("x>y"):
                             printf("x is %d but y is %d", x, y));

### 6.10.4 [Line control]

    1 Constraints
       The string literal of a #line directive, if present, shall be a character string literal.
        Semantics

    2   The line number of the current source line is one greater than the number of new-line
        characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
        file to the current token.

    3   A preprocessing directive of the form
           # line digit-sequence new-line
        causes the implementation to behave as if the following sequence of source lines begins
        with a source line that has a line number as specified by the digit sequence (interpreted as
        a decimal integer). The digit sequence shall not specify zero, nor a number greater than
        2147483647.

    4   A preprocessing directive of the form
           # line digit-sequence "s-char-sequenceopt" new-line
        sets the presumed line number similarly and changes the presumed name of the source
        file to be the contents of the character string literal.

    5   A preprocessing directive of the form
           # line pp-tokens new-line
        (that does not match one of the two previous forms) is permitted. The preprocessing
        tokens after line on the directive are processed just as in normal text (each identifier
        currently defined as a macro name is replaced by its replacement list of preprocessing
        tokens). The directive resulting after all replacements shall match one of the two
        previous forms and is then processed as appropriate.

### 6.10.5 [Error directive]

    1 Semantics
       A preprocessing directive of the form
           # error pp-tokensopt new-line
        causes the implementation to produce a diagnostic message that includes the specified
        sequence of preprocessing tokens.

### 6.10.6 [Pragma directive]

    1 Semantics
       A preprocessing directive of the form
           # pragma pp-tokensopt new-line
        where the preprocessing token STDC does not immediately follow pragma in the
        directive (prior to any macro replacement)[174] causes the implementation to behave in an
        implementation-defined manner. The behavior might cause translation to fail or cause the
        translator or the resulting program to behave in a non-conforming manner. Any such
        pragma that is not recognized by the implementation is ignored.

    Footnote 174) An implementation is not required to perform macro replacement in pragmas, but it is permitted
             except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
             replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
             implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
             but is not required to.

    2   If the preprocessing token STDC does immediately follow pragma in the directive (prior
        to any macro replacement), then no macro replacement is performed on the directive, and
        the directive shall have one of the following forms[175] whose meanings are described
        elsewhere:
           #pragma STDC FP_CONTRACT on-off-switch
           #pragma STDC FENV_ACCESS on-off-switch
           #pragma STDC CX_LIMITED_RANGE on-off-switch
           on-off-switch: one of
                       ON     OFF           DEFAULT
        Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
        (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).

    Footnote 175) See ‘‘future language directions’’ (6.11.8).

### 6.10.7 [Null directive]

    1 Semantics
       A preprocessing directive of the form
           # new-line
        has no effect.

### 6.10.8 [Predefined macro names]

    1   The values of the predefined macros listed in the following subclauses[176] (except for
        _ _FILE_ _ and _ _LINE_ _) remain constant throughout the translation unit.

    Footnote 176) See ‘‘future language directions’’ (6.11.9).

    2   None of these macro names, nor the identifier defined, shall be the subject of a
        #define or a #undef preprocessing directive. Any other predefined macro names
        shall begin with a leading underscore followed by an uppercase letter or a second
        underscore.

    3   The implementation shall not predefine the macro _ _cplusplus, nor shall it define it
        in any standard header.
        Forward references: standard headers (7.1.2).

### 6.10.8.1 [Mandatory macros]

    1   The following macro names shall be defined by the implementation:
        _ _DATE_ _ The date of translation of the preprocessing translation unit: a character
                   string literal of the form "Mmm dd yyyy", where the names of the
                   months are the same as those generated by the asctime function, and the
                   first character of dd is a space character if the value is less than 10. If the
                   date of translation is not available, an implementation-defined valid date
                   shall be supplied.
        _ _FILE_ _ The presumed name of the current source file (a character string literal).[177]
        _ _LINE_ _ The presumed line number (within the current source file) of the current
                   source line (an integer constant).[177]
        _ _STDC_ _ The integer constant 1, intended to indicate a conforming implementation.
        _ _STDC_HOSTED_ _ The integer constant 1 if the implementation is a hosted
                  implementation or the integer constant 0 if it is not.
        _ _STDC_VERSION_ _ The integer constant 201ymmL.[178]
        _ _TIME_ _ The time of translation of the preprocessing translation unit: a character
                   string literal of the form "hh:mm:ss" as in the time generated by the
                   asctime function. If the time of translation is not available, an
                   implementation-defined valid time shall be supplied.
        Forward references: the asctime function (7.27.3.1).

    Footnote 177) The presumed source file name and line number can be changed by the #line directive.

    Footnote 177) The presumed source file name and line number can be changed by the #line directive.

    Footnote 178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
             ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
             remain an integer constant of type long int that is increased with each revision of this International
             Standard.

### 6.10.8.2 [Environment macros]

    1   The following macro names are conditionally defined by the implementation:
        _ _STDC_ISO_10646_ _ An integer constant of the form yyyymmL (for example,
                  199712L). If this symbol is defined, then every character in the Unicode
                  required set, when stored in an object of type wchar_t, has the same
                  value as the short identifier of that character. The Unicode required set
                  consists of all the characters that are defined by ISO/IEC 10646, along with
                  all amendments and technical corrigenda, as of the specified year and
                  month. If some other encoding is used, the macro shall not be defined and
                  the actual encoding used is implementation-defined.
        _ _STDC_MB_MIGHT_NEQ_WC_ _ The integer constant 1, intended to indicate that, in
                  the encoding for wchar_t, a member of the basic character set need not
                  have a code value equal to its value when used as the lone character in an
                  integer character constant.
        _ _STDC_UTF_16_ _ The integer constant 1, intended to indicate that values of type
                  char16_t are UTF−16 encoded. If some other encoding is used, the
                  macro shall not be defined and the actual encoding used is implementation-
                  defined.
        _ _STDC_UTF_32_ _ The integer constant 1, intended to indicate that values of type
                  char32_t are UTF−32 encoded. If some other encoding is used, the
                  macro shall not be defined and the actual encoding used is implementation-
                  defined.
        Forward references: common definitions (7.19), unicode utilities (7.28).

### 6.10.8.3 [Conditional feature macros]

    1   The following macro names are conditionally defined by the implementation:
        _ _STDC_ANALYZABLE_ _ The integer constant 1, intended to indicate conformance to
                  the specifications in annex L (Analyzability).
        _ _STDC_IEC_559_ _ The integer constant 1, intended to indicate conformance to the
                  specifications in annex F (IEC 60559 floating-point arithmetic).
        _ _STDC_IEC_559_COMPLEX_ _ The integer constant 1, intended to indicate
                  adherence to the specifications in annex G (IEC 60559 compatible complex
                  arithmetic).
        _ _STDC_LIB_EXT1_ _ The integer constant 201ymmL, intended to indicate support
                  for the extensions defined in annex K (Bounds-checking interfaces).[179]
        _ _STDC_NO_ATOMICS_ _ The integer constant 1, intended to indicate that the
                  implementation does not support atomic types (including the _Atomic
                  type qualifier) and the <stdatomic.h> header.
        _ _STDC_NO_COMPLEX_ _ The integer constant 1, intended to indicate that the
                  implementation does not support complex types or the <complex.h>
                  header.
        _ _STDC_NO_THREADS_ _ The integer constant 1, intended to indicate that the
                  implementation does not support the <threads.h> header.
        _ _STDC_NO_VLA_ _ The integer constant 1, intended to indicate that the
                  implementation does not support variable length arrays or variably
                  modified types.

    Footnote 179) The intention is that this will remain an integer constant of type long int that is increased with
             each revision of this International Standard.

    2   An implementation that defines _ _STDC_NO_COMPLEX_ _ shall not define
        _ _STDC_IEC_559_COMPLEX_ _.

### 6.10.9 [Pragma operator]

    1 Semantics
       A unary operator expression of the form:
           _Pragma ( string-literal )
        is processed as follows: The string literal is destringized by deleting any encoding prefix,
        deleting the leading and trailing double-quotes, replacing each escape sequence \" by a
        double-quote, and replacing each escape sequence \\ by a single backslash. The
        resulting sequence of characters is processed through translation phase 3 to produce
        preprocessing tokens that are executed as if they were the pp-tokens in a pragma
        directive. The original four preprocessing tokens in the unary operator expression are
        removed.

    2   EXAMPLE       A directive of the form:
                 #pragma listing on "..\listing.dir"
        can also be expressed as:
                 _Pragma ( "listing on \"..\\listing.dir\"" )
        The latter form is processed in the same way whether it appears literally as shown, or results from macro
        replacement, as in:
                 #define LISTING(x) PRAGMA(listing on #x)
                 #define PRAGMA(x) _Pragma(#x)
                 LISTING ( ..\listing.dir )

### 6.11 [Future language directions]

### 6.11.1 [Floating types]

    1   Future standardization may include additional floating-point types, including those with
        greater range, precision, or both than long double.

### 6.11.2 [Linkages of identifiers]

    1   Declaring an identifier with internal linkage at file scope without the static storage-
        class specifier is an obsolescent feature.

### 6.11.3 [External names]

    1   Restriction of the significance of an external name to fewer than 255 characters
        (considering each universal character name or extended source character as a single
        character) is an obsolescent feature that is a concession to existing implementations.

### 6.11.4 [Character escape sequences]

    1   Lowercase letters as escape sequences are reserved for future standardization. Other
        characters may be used in extensions.

### 6.11.5 [Storage-class specifiers]

    1   The placement of a storage-class specifier other than at the beginning of the declaration
        specifiers in a declaration is an obsolescent feature.

### 6.11.6 [Function declarators]

    1   The use of function declarators with empty parentheses (not prototype-format parameter
        type declarators) is an obsolescent feature.

### 6.11.7 [Function definitions]

    1   The use of function definitions with separate parameter identifier and declaration lists
        (not prototype-format parameter type and identifier declarators) is an obsolescent feature.

### 6.11.8 [Pragma directives]

    1   Pragmas whose first preprocessing token is STDC are reserved for future standardization.

### 6.11.9 [Predefined macro names]

    1   Macro names beginning with _ _STDC_ are reserved for future standardization.

### 7. [Library]

### 7.1 [Introduction]

### 7.1.1 [Definitions of terms]

    1   A string is a contiguous sequence of characters terminated by and including the first null
        character. The term multibyte string is sometimes used instead to emphasize special
        processing given to multibyte characters contained in the string or to avoid confusion
        with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
        character. The length of a string is the number of bytes preceding the null character and
        the value of a string is the sequence of the values of the contained characters, in order.

    2   The decimal-point character is the character used by functions that convert floating-point
        numbers to or from character sequences to denote the beginning of the fractional part of
        such character sequences.[180] It is represented in the text and examples by a period, but
        may be changed by the setlocale function.

    Footnote 180) The functions that make use of the decimal-point character are the numeric conversion functions
             (7.22.1, 7.29.4.1) and the formatted input/output functions (7.21.6, 7.29.2).

    3   A null wide character is a wide character with code value zero.

    4   A wide string is a contiguous sequence of wide characters terminated by and including
        the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
        addressed) wide character. The length of a wide string is the number of wide characters
        preceding the null wide character and the value of a wide string is the sequence of code
        values of the contained wide characters, in order.

    5   A shift sequence is a contiguous sequence of bytes within a multibyte string that
        (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
        corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
        character.[181]
        Forward references: character handling (7.4), the setlocale function (7.11.1.1).

    Footnote 181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
             enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
             sequence of maximum length. Whether these counts provide for more than one shift sequence is the
             implementation’s choice.

### 7.1.2 [Standard headers]

    1   Each library function is declared, with a type that includes a prototype, in a header,[182]
        whose contents are made available by the #include preprocessing directive. The
        header declares a set of related functions, plus any necessary types and additional macros
        needed to facilitate their use. Declarations of types described in this clause shall not
        include type qualifiers, unless explicitly stated otherwise.

    Footnote 182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
             necessarily valid source file names.

    2   The standard headers are[183]
               <assert.h>                      <math.h>                        <stdlib.h>
               <complex.h>                     <setjmp.h>                      <stdnoreturn.h>
               <ctype.h>                       <signal.h>                      <string.h>
               <errno.h>                       <stdalign.h>                    <tgmath.h>
               <fenv.h>                        <stdarg.h>                      <threads.h>
               <float.h>                       <stdatomic.h>                   <time.h>
               <inttypes.h>                    <stdbool.h>                     <uchar.h>
               <iso646.h>                      <stddef.h>                      <wchar.h>
               <limits.h>                      <stdint.h>                      <wctype.h>
               <locale.h>                      <stdio.h>

    Footnote 183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that
             implementations need not support; see 6.10.8.3.

    3   If a file with the same name as one of the above < and > delimited sequences, not
        provided as part of the implementation, is placed in any of the standard places that are
        searched for included source files, the behavior is undefined.

    4   Standard headers may be included in any order; each may be included more than once in
        a given scope, with no effect different from being included only once, except that the
        effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
        used, a header shall be included outside of any external declaration or definition, and it
        shall first be included before the first reference to any of the functions or objects it
        declares, or to any of the types or macros it defines. However, if an identifier is declared
        or defined in more than one header, the second and subsequent associated headers may be
        included after the initial reference to the identifier. The program shall not have any
        macros with names lexically identical to keywords currently defined prior to the inclusion
        of the header or when any macro defined in the header is expanded.

    5   Any definition of an object-like macro described in this clause shall expand to code that is
        fully protected by parentheses where necessary, so that it groups in an arbitrary
        expression as if it were a single identifier.

    6   Any declaration of a library function shall have external linkage.

    7   A summary of the contents of the standard headers is given in annex B.
        Forward references: diagnostics (7.2).

### 7.1.3 [Reserved identifiers]

    1   Each header declares or defines all identifiers listed in its associated subclause, and
        optionally declares or defines identifiers listed in its associated future library directions
        subclause and identifiers which are always reserved either for any use or for use as file
        scope identifiers.
        — All identifiers that begin with an underscore and either an uppercase letter or another
          underscore are always reserved for any use.
        — All identifiers that begin with an underscore are always reserved for use as identifiers
          with file scope in both the ordinary and tag name spaces.
        — Each macro name in any of the following subclauses (including the future library
          directions) is reserved for use as specified if any of its associated headers is included;
          unless explicitly stated otherwise (see 7.1.4).
        — All identifiers with external linkage in any of the following subclauses (including the
          future library directions) and errno are always reserved for use as identifiers with
          external linkage.[184]
        — Each identifier with file scope listed in any of the following subclauses (including the
          future library directions) is reserved for use as a macro name and as an identifier with
          file scope in the same name space if any of its associated headers is included.

    Footnote 184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
             va_copy, and va_end.

    2   No other identifiers are reserved. If the program declares or defines an identifier in a
        context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
        identifier as a macro name, the behavior is undefined.

    3   If the program removes (with #undef) any macro definition of an identifier in the first
        group listed above, the behavior is undefined.

### 7.1.4 [Use of library functions]

    1   Each of the following statements applies unless explicitly stated otherwise in the detailed
        descriptions that follow: If an argument to a function has an invalid value (such as a value
        outside the domain of the function, or a pointer outside the address space of the program,
        or a null pointer, or a pointer to non-modifiable storage when the corresponding
        parameter is not const-qualified) or a type (after promotion) not expected by a function
        with variable number of arguments, the behavior is undefined. If a function argument is
        described as being an array, the pointer actually passed to the function shall have a value
        such that all address computations and accesses to objects (that would be valid if the
        pointer did point to the first element of such an array) are in fact valid. Any function
        declared in a header may be additionally implemented as a function-like macro defined in
        the header, so if a library function is declared explicitly when its header is included, one
        of the techniques shown below can be used to ensure the declaration is not affected by
        such a macro. Any macro definition of a function can be suppressed locally by enclosing
        the name of the function in parentheses, because the name is then not followed by the left
        parenthesis that indicates expansion of a macro function name. For the same syntactic
        reason, it is permitted to take the address of a library function even if it is also defined as
        a macro.[185] The use of #undef to remove any macro definition will also ensure that an
        actual function is referred to. Any invocation of a library function that is implemented as
        a macro shall expand to code that evaluates each of its arguments exactly once, fully
        protected by parentheses where necessary, so it is generally safe to use arbitrary
        expressions as arguments.[186] Likewise, those function-like macros described in the
        following subclauses may be invoked in an expression anywhere a function with a
        compatible return type could be called.[187] All object-like macros listed as expanding to
        integer constant expressions shall additionally be suitable for use in #if preprocessing
        directives.

    Footnote 185) This means that an implementation shall provide an actual function for each library function, even if it
             also provides a macro for that function.

    Footnote 186) Such macros might not contain the sequence points that the corresponding function calls do.

    Footnote 187) Because external identifiers and some macro names beginning with an underscore are reserved,
             implementations may provide special semantics for such names. For example, the identifier
             _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
             appropriate header could specify
                      #define abs(x) _BUILTIN_abs(x)
             for a compiler whose code generator will accept it.
             In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
             function may write
                      #undef abs
             whether the implementation’s header provides a macro implementation of abs or a built-in
             implementation. The prototype for the function, which precedes and is hidden by any macro
             definition, is thereby revealed also.

    2   Provided that a library function can be declared without reference to any type defined in a
        header, it is also permissible to declare the function and use it without including its
        associated header.

    3   There is a sequence point immediately before a library function returns.

    4   The functions in the standard library are not guaranteed to be reentrant and may modify
        objects with static or thread storage duration.[188]

    Footnote 188) Thus, a signal handler cannot, in general, call standard library functions.

    5   Unless explicitly stated otherwise in the detailed descriptions that follow, library
        functions shall prevent data races as follows: A library function shall not directly or
        indirectly access objects accessible by threads other than the current thread unless the
        objects are accessed directly or indirectly via the function’s arguments. A library
        function shall not directly or indirectly modify objects accessible by threads other than
        the current thread unless the objects are accessed directly or indirectly via the function’s
        non-const arguments.[189] Implementations may share their own internal objects between
        threads if the objects are not visible to users and are protected against data races.

    Footnote 189) This means, for example, that an implementation is not permitted to use a static object for internal
             purposes without synchronization because it could cause a data race even in programs that do not
             explicitly share objects between threads. Similarly, an implementation of memcpy is not permitted to
             copy bytes beyond the specified length of the destination object and then restore the original values
             because it could cause a data race if the program shared those bytes between threads.

    6   Unless otherwise specified, library functions shall perform all operations solely within the
        current thread if those operations have effects that are visible to users.[190]

    Footnote 190) This allows implementations to parallelize operations if there are no visible side effects.

    7   EXAMPLE        The function atoi may be used in any of several ways:
        — by use of its associated header (possibly generating a macro expansion)
                     #include <stdlib.h>
                     const char *str;
                     /* ... */
                     i = atoi(str);
        — by use of its associated header (assuredly generating a true function reference)
                #include <stdlib.h>
                #undef atoi
                const char *str;
                /* ... */
                i = atoi(str);
       or
                #include <stdlib.h>
                const char *str;
                /* ... */
                i = (atoi)(str);
    — by explicit declaration
                extern int atoi(const char *);
                const char *str;
                /* ... */
                i = atoi(str);

### 7.2 [Diagnostics <assert.h>]

    1   The header <assert.h> defines the assert and static_assert macros and
        refers to another macro,
                NDEBUG
        which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
        point in the source file where <assert.h> is included, the assert macro is defined
        simply as
                #define assert(ignore) ((void)0)
        The assert macro is redefined according to the current state of NDEBUG each time that
        <assert.h> is included.

    2   The assert macro shall be implemented as a macro, not as an actual function. If the
        macro definition is suppressed in order to access an actual function, the behavior is
        undefined.

    3   The macro
                static_assert
        expands to _Static_assert.

### 7.2.1 [Program diagnostics]

### 7.2.1.1 [The assert macro]

    1 Synopsis
               #include <assert.h>
                void assert(scalar expression);
        Description

    2   The assert macro puts diagnostic tests into programs; it expands to a void expression.
        When it is executed, if expression (which shall have a scalar type) is false (that is,
        compares equal to 0), the assert macro writes information about the particular call that
        failed (including the text of the argument, the name of the source file, the source line
        number, and the name of the enclosing function — the latter are respectively the values of
        the preprocessing macros _ _FILE_ _ and _ _LINE_ _ and of the identifier
        _ _func_ _) on the standard error stream in an implementation-defined format.[191] It
        then calls the abort function.
        Returns

    Footnote 191) The message written might be of the form:
             Assertion failed: expression, function abc, file xyz, line nnn.

    3   The assert macro returns no value.
        Forward references: the abort function (7.22.4.1).

### 7.3 [Complex arithmetic <complex.h>]

### 7.3.1 [Introduction]

    1   The header <complex.h> defines macros and declares functions that support complex
        arithmetic.[192]

    Footnote 192) See ‘‘future library directions’’ (7.31.1).

    2   Implementations that define the macro _ _STDC_NO_COMPLEX_ _ need not provide
        this header nor support any of its facilities.

    3   Each synopsis specifies a family of functions consisting of a principal function with one
        or more double complex parameters and a double complex or double return
        value; and other functions with the same name but with f and l suffixes which are
        corresponding functions with float and long double parameters and return values.

    4   The macro
                 complex
        expands to _Complex; the macro
                 _Complex_I
        expands to a constant expression of type const float _Complex, with the value of
        the imaginary unit.[193]

    Footnote 193) The imaginary unit is a number i such that i 2 = −1.

    5   The macros
                 imaginary
        and
                 _Imaginary_I
        are defined if and only if the implementation supports imaginary types;[194] if defined,
        they expand to _Imaginary and a constant expression of type const float
        _Imaginary with the value of the imaginary unit.

    Footnote 194) A specification for imaginary types is in informative annex G.

    6   The macro
                 I
        expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
        defined, I shall expand to _Complex_I.

    7   Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
        redefine the macros complex, imaginary, and I.
        Forward references: IEC 60559-compatible complex arithmetic (annex G).

### 7.3.2 [Conventions]

    1   Values are interpreted as radians, not degrees. An implementation may set errno but is
        not required to.

### 7.3.3 [Branch cuts]

    1   Some of the functions below have branch cuts, across which the function is
        discontinuous. For implementations with a signed zero (including all IEC 60559
        implementations) that follow the specifications of annex G, the sign of zero distinguishes
        one side of a cut from another so the function is continuous (except for format
        limitations) as the cut is approached from either side. For example, for the square root
        function, which has a branch cut along the negative real axis, the top of the cut, with
        imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
        imaginary part −0, maps to the negative imaginary axis.

    2   Implementations that do not support a signed zero (see annex F) cannot distinguish the
        sides of branch cuts. These implementations shall map a cut so the function is continuous
        as the cut is approached coming around the finite endpoint of the cut in a counter
        clockwise direction. (Branch cuts for the functions specified here have just one finite
        endpoint.) For example, for the square root function, coming counter clockwise around
        the finite endpoint of the cut along the negative real axis approaches the cut from above,
        so the cut maps to the positive imaginary axis.

### 7.3.4 [The CX_LIMITED_RANGE pragma]

    1 Synopsis
              #include <complex.h>
               #pragma STDC CX_LIMITED_RANGE on-off-switch
        Description

    2   The usual mathematical formulas for complex multiply, divide, and absolute value are
        problematic because of their treatment of infinities and because of undue overflow and
        underflow. The CX_LIMITED_RANGE pragma can be used to inform the
        implementation that (where the state is ‘‘on’’) the usual mathematical formulas are
        acceptable.[195] The pragma can occur either outside external declarations or preceding all
        explicit declarations and statements inside a compound statement. When outside external
        declarations, the pragma takes effect from its occurrence until another
        CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
        When inside a compound statement, the pragma takes effect from its occurrence until
        another CX_LIMITED_RANGE pragma is encountered (including within a nested
        compound statement), or until the end of the compound statement; at the end of a
        compound statement the state for the pragma is restored to its condition just before the
        compound statement. If this pragma is used in any other context, the behavior is
        undefined. The default state for the pragma is ‘‘off’’.

    Footnote 195) The purpose of the pragma is to allow the implementation to use the formulas:
                (x + iy) × (u + iv) = (xu − yv) + i(yu + xv)
                (x + iy) / (u + iv) = [(xu + yv) + i(yu − xv)]/(u2 + v 2 )
                | x + iy | = √
                             ⎯⎯⎯⎯⎯
                               x 2 + y2
             where the programmer can determine they are safe.

### 7.3.5 [Trigonometric functions]

### 7.3.5.1 [The cacos functions]

    1 Synopsis
               #include <complex.h>
                double complex cacos(double complex z);
                float complex cacosf(float complex z);
                long double complex cacosl(long double complex z);
        Description

    2   The cacos functions compute the complex arc cosine of z, with branch cuts outside the
        interval [−1, +1] along the real axis.
        Returns

    3   The cacos functions return the complex arc cosine value, in the range of a strip
        mathematically unbounded along the imaginary axis and in the interval [0, π ] along the
        real axis.

### 7.3.5.2 [The casin functions]

    1 Synopsis
               #include <complex.h>
                double complex casin(double complex z);
                float complex casinf(float complex z);
                long double complex casinl(long double complex z);
        Description

    2   The casin functions compute the complex arc sine of z, with branch cuts outside the
        interval [−1, +1] along the real axis.
        Returns

    3   The casin functions return the complex arc sine value, in the range of a strip
        mathematically unbounded along the imaginary axis and in the interval [−π /2, +π /2]
        along the real axis.

### 7.3.5.3 [The catan functions]

    1 Synopsis
              #include <complex.h>
               double complex catan(double complex z);
               float complex catanf(float complex z);
               long double complex catanl(long double complex z);
        Description

    2   The catan functions compute the complex arc tangent of z, with branch cuts outside the
        interval [−i, +i] along the imaginary axis.
        Returns

    3   The catan functions return the complex arc tangent value, in the range of a strip
        mathematically unbounded along the imaginary axis and in the interval [−π /2, +π /2]
        along the real axis.

### 7.3.5.4 [The ccos functions]

    1 Synopsis
              #include <complex.h>
               double complex ccos(double complex z);
               float complex ccosf(float complex z);
               long double complex ccosl(long double complex z);
        Description

    2   The ccos functions compute the complex cosine of z.
        Returns

    3   The ccos functions return the complex cosine value.

### 7.3.5.5 [The csin functions]

    1 Synopsis
              #include <complex.h>
               double complex csin(double complex z);
               float complex csinf(float complex z);
               long double complex csinl(long double complex z);
        Description

    2   The csin functions compute the complex sine of z.
        Returns

    3   The csin functions return the complex sine value.

### 7.3.5.6 [The ctan functions]

    1 Synopsis
              #include <complex.h>
               double complex ctan(double complex z);
               float complex ctanf(float complex z);
               long double complex ctanl(long double complex z);
        Description

    2   The ctan functions compute the complex tangent of z.
        Returns

    3   The ctan functions return the complex tangent value.

### 7.3.6 [Hyperbolic functions]

### 7.3.6.1 [The cacosh functions]

    1 Synopsis
              #include <complex.h>
               double complex cacosh(double complex z);
               float complex cacoshf(float complex z);
               long double complex cacoshl(long double complex z);
        Description

    2   The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
        cut at values less than 1 along the real axis.
        Returns

    3   The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
        half-strip of nonnegative values along the real axis and in the interval [−iπ , +iπ ] along the
        imaginary axis.

### 7.3.6.2 [The casinh functions]

    1 Synopsis
              #include <complex.h>
               double complex casinh(double complex z);
               float complex casinhf(float complex z);
               long double complex casinhl(long double complex z);
        Description

    2   The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
        outside the interval [−i, +i] along the imaginary axis.
        Returns

    3   The casinh functions return the complex arc hyperbolic sine value, in the range of a
        strip mathematically unbounded along the real axis and in the interval [−iπ /2, +iπ /2]
        along the imaginary axis.

### 7.3.6.3 [The catanh functions]

    1 Synopsis
              #include <complex.h>
               double complex catanh(double complex z);
               float complex catanhf(float complex z);
               long double complex catanhl(long double complex z);
        Description

    2   The catanh functions compute the complex arc hyperbolic tangent of z, with branch
        cuts outside the interval [−1, +1] along the real axis.
        Returns

    3   The catanh functions return the complex arc hyperbolic tangent value, in the range of a
        strip mathematically unbounded along the real axis and in the interval [−iπ /2, +iπ /2]
        along the imaginary axis.

### 7.3.6.4 [The ccosh functions]

    1 Synopsis
              #include <complex.h>
               double complex ccosh(double complex z);
               float complex ccoshf(float complex z);
               long double complex ccoshl(long double complex z);
        Description

    2   The ccosh functions compute the complex hyperbolic cosine of z.
        Returns

    3   The ccosh functions return the complex hyperbolic cosine value.

### 7.3.6.5 [The csinh functions]

    1 Synopsis
              #include <complex.h>
               double complex csinh(double complex z);
               float complex csinhf(float complex z);
               long double complex csinhl(long double complex z);
        Description

    2   The csinh functions compute the complex hyperbolic sine of z.
        Returns

    3   The csinh functions return the complex hyperbolic sine value.

### 7.3.6.6 [The ctanh functions]

    1 Synopsis
              #include <complex.h>
               double complex ctanh(double complex z);
               float complex ctanhf(float complex z);
               long double complex ctanhl(long double complex z);
        Description

    2   The ctanh functions compute the complex hyperbolic tangent of z.
        Returns

    3   The ctanh functions return the complex hyperbolic tangent value.

### 7.3.7 [Exponential and logarithmic functions]

### 7.3.7.1 [The cexp functions]

    1 Synopsis
              #include <complex.h>
               double complex cexp(double complex z);
               float complex cexpf(float complex z);
               long double complex cexpl(long double complex z);
        Description

    2   The cexp functions compute the complex base-e exponential of z.
        Returns

    3   The cexp functions return the complex base-e exponential value.

### 7.3.7.2 [The clog functions]

    1 Synopsis
              #include <complex.h>
               double complex clog(double complex z);
               float complex clogf(float complex z);
               long double complex clogl(long double complex z);
        Description

    2   The clog functions compute the complex natural (base-e) logarithm of z, with a branch
        cut along the negative real axis.
        Returns

    3   The clog functions return the complex natural logarithm value, in the range of a strip
        mathematically unbounded along the real axis and in the interval [−iπ , +iπ ] along the
        imaginary axis.

### 7.3.8 [Power and absolute-value functions]

### 7.3.8.1 [The cabs functions]

    1 Synopsis
              #include <complex.h>
               double cabs(double complex z);
               float cabsf(float complex z);
               long double cabsl(long double complex z);
        Description

    2   The cabs functions compute the complex absolute value (also called norm, modulus, or
        magnitude) of z.
        Returns

    3   The cabs functions return the complex absolute value.

### 7.3.8.2 [The cpow functions]

    1 Synopsis
              #include <complex.h>
               double complex cpow(double complex x, double complex y);
               float complex cpowf(float complex x, float complex y);
               long double complex cpowl(long double complex x,
                    long double complex y);
        Description

    2   The cpow functions compute the complex power function xy , with a branch cut for the
        first parameter along the negative real axis.
        Returns

    3   The cpow functions return the complex power function value.

### 7.3.8.3 [The csqrt functions]

    1 Synopsis
              #include <complex.h>
               double complex csqrt(double complex z);
               float complex csqrtf(float complex z);
               long double complex csqrtl(long double complex z);
        Description

    2   The csqrt functions compute the complex square root of z, with a branch cut along the
        negative real axis.
        Returns

    3   The csqrt functions return the complex square root value, in the range of the right half-
        plane (including the imaginary axis).

### 7.3.9 [Manipulation functions]

### 7.3.9.1 [The carg functions]

    1 Synopsis
              #include <complex.h>
               double carg(double complex z);
               float cargf(float complex z);
               long double cargl(long double complex z);
        Description

    2   The carg functions compute the argument (also called phase angle) of z, with a branch
        cut along the negative real axis.
        Returns

    3   The carg functions return the value of the argument in the interval [−π , +π ].

### 7.3.9.2 [The cimag functions]

    1 Synopsis
              #include <complex.h>
               double cimag(double complex z);
               float cimagf(float complex z);
               long double cimagl(long double complex z);
        Description

    2   The cimag functions compute the imaginary part of z.[196]
        Returns

    Footnote 196) For a variable z of complex type, z == creal(z) + cimag(z)*I.

    3   The cimag functions return the imaginary part value (as a real).

### 7.3.9.3 [The CMPLX macros]

    1 Synopsis
              #include <complex.h>
               double complex CMPLX(double x, double y);
               float complex CMPLXF(float x, float y);
               long double complex CMPLXL(long double x, long double y);
        Description

    2   The CMPLX macros expand to an expression of the specified complex type, with the real
        part having the (converted) value of x and the imaginary part having the (converted)
        value of y. The resulting expression shall be suitable for use as an initializer for an object
        with static or thread storage duration, provided both arguments are likewise suitable.
        Returns

    3   The CMPLX macros return the complex value x + i y.

    4   NOTE    These macros act as if the implementation supported imaginary types and the definitions were:
             #define CMPLX(x, y)  ((double complex)((double)(x) + \
                                           _Imaginary_I * (double)(y)))
             #define CMPLXF(x, y) ((float complex)((float)(x) + \
                                           _Imaginary_I * (float)(y)))
             #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
                                           _Imaginary_I * (long double)(y)))

### 7.3.9.4 [The conj functions]

    1 Synopsis
              #include <complex.h>
               double complex conj(double complex z);
               float complex conjf(float complex z);
               long double complex conjl(long double complex z);
        Description

    2   The conj functions compute the complex conjugate of z, by reversing the sign of its
        imaginary part.
        Returns

    3   The conj functions return the complex conjugate value.

### 7.3.9.5 [The cproj functions]

    1 Synopsis
              #include <complex.h>
               double complex cproj(double complex z);
               float complex cprojf(float complex z);
               long double complex cprojl(long double complex z);
        Description

    2   The cproj functions compute a projection of z onto the Riemann sphere: z projects to
        z except that all complex infinities (even those with one infinite part and one NaN part)
        project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
        equivalent to
               INFINITY + I * copysign(0.0, cimag(z))
        Returns

    3   The cproj functions return the value of the projection onto the Riemann sphere.

### 7.3.9.6 [The creal functions]

    1 Synopsis
              #include <complex.h>
               double creal(double complex z);
               float crealf(float complex z);
               long double creall(long double complex z);
        Description

    2   The creal functions compute the real part of z.[197]
        Returns

    Footnote 197) For a variable z of complex type, z == creal(z) + cimag(z)*I.

    3   The creal functions return the real part value.

### 7.4 [Character handling <ctype.h>]

    1   The header <ctype.h> declares several functions useful for classifying and mapping
        characters.[198] In all cases the argument is an int, the value of which shall be
        representable as an unsigned char or shall equal the value of the macro EOF. If the
        argument has any other value, the behavior is undefined.

    Footnote 198) See ‘‘future library directions’’ (7.31.2).

    2   The behavior of these functions is affected by the current locale. Those functions that
        have locale-specific aspects only when not in the "C" locale are noted below.

    3   The term printing character refers to a member of a locale-specific set of characters, each
        of which occupies one printing position on a display device; the term control character
        refers to a member of a locale-specific set of characters that are not printing
        characters.[199] All letters and digits are printing characters.
        Forward references: EOF (7.21.1), localization (7.11).

    Footnote 199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
             whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
             values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).

### 7.4.1 [Character classification functions]

    1   The functions in this subclause return nonzero (true) if and only if the value of the
        argument c conforms to that in the description of the function.

### 7.4.1.1 [The isalnum function]

    1 Synopsis
                #include <ctype.h>
                 int isalnum(int c);
        Description

    2   The isalnum function tests for any character for which isalpha or isdigit is true.

### 7.4.1.2 [The isalpha function]

    1 Synopsis
                #include <ctype.h>
                 int isalpha(int c);
        Description

    2   The isalpha function tests for any character for which isupper or islower is true,
        or any character that is one of a locale-specific set of alphabetic characters for which
        none of iscntrl, isdigit, ispunct, or isspace is true.[200] In the "C" locale,
        isalpha returns true only for the characters for which isupper or islower is true.

    Footnote 200) The functions islower and isupper test true or false separately for each of these additional
             characters; all four combinations are possible.

### 7.4.1.3 [The isblank function]

    1 Synopsis
               #include <ctype.h>
                int isblank(int c);
        Description

    2   The isblank function tests for any character that is a standard blank character or is one
        of a locale-specific set of characters for which isspace is true and that is used to
        separate words within a line of text. The standard blank characters are the following:
        space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
        for the standard blank characters.

### 7.4.1.4 [The iscntrl function]

    1 Synopsis
               #include <ctype.h>
                int iscntrl(int c);
        Description

    2   The iscntrl function tests for any control character.

### 7.4.1.5 [The isdigit function]

    1 Synopsis
               #include <ctype.h>
                int isdigit(int c);
        Description

    2   The isdigit function tests for any decimal-digit character (as defined in 5.2.1).

### 7.4.1.6 [The isgraph function]

    1 Synopsis
               #include <ctype.h>
                int isgraph(int c);
        Description

    2   The isgraph function tests for any printing character except space (' ').

### 7.4.1.7 [The islower function]

    1 Synopsis
              #include <ctype.h>
               int islower(int c);
        Description

    2   The islower function tests for any character that is a lowercase letter or is one of a
        locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
        isspace is true. In the "C" locale, islower returns true only for the lowercase
        letters (as defined in 5.2.1).

### 7.4.1.8 [The isprint function]

    1 Synopsis
              #include <ctype.h>
               int isprint(int c);
        Description

    2   The isprint function tests for any printing character including space (' ').

### 7.4.1.9 [The ispunct function]

    1 Synopsis
              #include <ctype.h>
               int ispunct(int c);
        Description

    2   The ispunct function tests for any printing character that is one of a locale-specific set
        of punctuation characters for which neither isspace nor isalnum is true. In the "C"
        locale, ispunct returns true for every printing character for which neither isspace
        nor isalnum is true.

### 7.4.1.10 [The isspace function]

    1 Synopsis
              #include <ctype.h>
               int isspace(int c);
        Description

    2   The isspace function tests for any character that is a standard white-space character or
        is one of a locale-specific set of characters for which isalnum is false. The standard
        white-space characters are the following: space (' '), form feed ('\f'), new-line
        ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
        "C" locale, isspace returns true only for the standard white-space characters.

### 7.4.1.11 [The isupper function]

    1 Synopsis
              #include <ctype.h>
               int isupper(int c);
        Description

    2   The isupper function tests for any character that is an uppercase letter or is one of a
        locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
        isspace is true. In the "C" locale, isupper returns true only for the uppercase
        letters (as defined in 5.2.1).

### 7.4.1.12 [The isxdigit function]

    1 Synopsis
              #include <ctype.h>
               int isxdigit(int c);
        Description

    2   The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).

### 7.4.2 [Character case mapping functions]

### 7.4.2.1 [The tolower function]

    1 Synopsis
              #include <ctype.h>
               int tolower(int c);
        Description

    2   The tolower function converts an uppercase letter to a corresponding lowercase letter.
        Returns

    3   If the argument is a character for which isupper is true and there are one or more
        corresponding characters, as specified by the current locale, for which islower is true,
        the tolower function returns one of the corresponding characters (always the same one
        for any given locale); otherwise, the argument is returned unchanged.

### 7.4.2.2 [The toupper function]

    1 Synopsis
              #include <ctype.h>
               int toupper(int c);
        Description

    2   The toupper function converts a lowercase letter to a corresponding uppercase letter.
        Returns

    3   If the argument is a character for which islower is true and there are one or more
        corresponding characters, as specified by the current locale, for which isupper is true,
        the toupper function returns one of the corresponding characters (always the same one
        for any given locale); otherwise, the argument is returned unchanged.

### 7.5 [Errors <errno.h>]

    1   The header <errno.h> defines several macros, all relating to the reporting of error
        conditions.

    2   The macros are
                 EDOM
                 EILSEQ
                 ERANGE
        which expand to integer constant expressions with type int, distinct positive values, and
        which are suitable for use in #if preprocessing directives; and
                 errno
        which expands to a modifiable lvalue[201] that has type int and thread local storage
        duration, the value of which is set to a positive error number by several library functions.
        If a macro definition is suppressed in order to access an actual object, or a program
        defines an identifier with the name errno, the behavior is undefined.

    Footnote 201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
             resulting from a function call (for example, *errno()).

    3   The value of errno in the initial thread is zero at program startup (the initial value of
        errno in other threads is an indeterminate value), but is never set to zero by any library
        function.[202] The value of errno may be set to nonzero by a library function call
        whether or not there is an error, provided the use of errno is not documented in the
        description of the function in this International Standard.

    Footnote 202) Thus, a program that uses errno for error checking should set it to zero before a library function call,
             then inspect it before a subsequent library function call. Of course, a library function can save the
             value of errno on entry and then set it to zero, as long as the original value is restored if errno’s
             value is still zero just before the return.

    4   Additional macro definitions, beginning with E and a digit or E and an uppercase
        letter,[203] may also be specified by the implementation.

    Footnote 203) See ‘‘future library directions’’ (7.31.3).

### 7.6 [Floating-point environment <fenv.h>]

    1   The header <fenv.h> defines several macros, and declares types and functions that
        provide access to the floating-point environment. The floating-point environment refers
        collectively to any floating-point status flags and control modes supported by the
        implementation.[204] A floating-point status flag is a system variable whose value is set
        (but never cleared) when a floating-point exception is raised, which occurs as a side effect
        of exceptional floating-point arithmetic to provide auxiliary information.[205] A floating-
        point control mode is a system variable whose value may be set by the user to affect the
        subsequent behavior of floating-point arithmetic.

    Footnote 204) This header is designed to support the floating-point exception status flags and directed-rounding
             control modes required by IEC 60559, and other similar floating-point state information. It is also
             designed to facilitate code portability among all systems.

    Footnote 205) A floating-point status flag is not an object and can be set more than once within an expression.

    2   The floating-point environment has thread storage duration. The initial state for a
        thread’s floating-point environment is the current state of the floating-point environment
        of the thread that creates it at the time of creation.

    3   Certain programming conventions support the intended model of use for the floating-
        point environment:[206]
        — a function call does not alter its caller’s floating-point control modes, clear its caller’s
          floating-point status flags, nor depend on the state of its caller’s floating-point status
          flags unless the function is so documented;
        — a function call is assumed to require default floating-point control modes, unless its
          documentation promises otherwise;
        — a function call is assumed to have the potential for raising floating-point exceptions,
          unless its documentation promises otherwise.

    Footnote 206) With these conventions, a programmer can safely assume default floating-point control modes (or be
             unaware of them). The responsibilities associated with accessing the floating-point environment fall
             on the programmer or program that does so explicitly.

    4   The type
                 fenv_t
        represents the entire floating-point environment.

    5   The type
                 fexcept_t
        represents the floating-point status flags collectively, including any status the
        implementation associates with the flags.

    6   Each of the macros
                 FE_DIVBYZERO
                 FE_INEXACT
                 FE_INVALID
                 FE_OVERFLOW
                 FE_UNDERFLOW
        is defined if and only if the implementation supports the floating-point exception by
        means of the functions in 7.6.2.[207] Additional implementation-defined floating-point
        exceptions, with macro definitions beginning with FE_ and an uppercase letter,[208] may
        also be specified by the implementation. The defined macros expand to integer constant
        expressions with values such that bitwise ORs of all combinations of the macros result in
        distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in
        zero.[209]

    Footnote 207) The implementation supports a floating-point exception if there are circumstances where a call to at
             least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not
             necessary for all the functions to succeed all the time.

    Footnote 208) See ‘‘future library directions’’ (7.31.4).

    Footnote 209) The macros should be distinct powers of two.

    7   The macro
                 FE_ALL_EXCEPT
        is simply the bitwise OR of all floating-point exception macros defined by the
        implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.

    8   Each of the macros
                 FE_DOWNWARD
                 FE_TONEAREST
                 FE_TOWARDZERO
                 FE_UPWARD
        is defined if and only if the implementation supports getting and setting the represented
        rounding direction by means of the fegetround and fesetround functions.
        Additional implementation-defined rounding directions, with macro definitions beginning
        with FE_ and an uppercase letter,[210] may also be specified by the implementation. The
        defined macros expand to integer constant expressions whose values are distinct
        nonnegative values.[211]

    Footnote 210) See ‘‘future library directions’’ (7.31.4).

    Footnote 211) Even though the rounding direction macros may expand to constants corresponding to the values of
             FLT_ROUNDS, they are not required to do so.

    9    The macro
                  FE_DFL_ENV
         represents the default floating-point environment — the one installed at program startup
         — and has type ‘‘pointer to const-qualified fenv_t’’. It can be used as an argument to
         <fenv.h> functions that manage the floating-point environment.

    10   Additional implementation-defined environments, with macro definitions beginning with
         FE_ and an uppercase letter,[212] and having type ‘‘pointer to const-qualified fenv_t’’,
         may also be specified by the implementation.

    Footnote 212) See ‘‘future library directions’’ (7.31.4).

### 7.6.1 [The FENV_ACCESS pragma]

    1 Synopsis
                 #include <fenv.h>
                  #pragma STDC FENV_ACCESS on-off-switch
         Description

    2    The FENV_ACCESS pragma provides a means to inform the implementation when a
         program might access the floating-point environment to test floating-point status flags or
         run under non-default floating-point control modes.[213] The pragma shall occur either
         outside external declarations or preceding all explicit declarations and statements inside a
         compound statement. When outside external declarations, the pragma takes effect from
         its occurrence until another FENV_ACCESS pragma is encountered, or until the end of
         the translation unit. When inside a compound statement, the pragma takes effect from its
         occurrence until another FENV_ACCESS pragma is encountered (including within a
         nested compound statement), or until the end of the compound statement; at the end of a
         compound statement the state for the pragma is restored to its condition just before the
         compound statement. If this pragma is used in any other context, the behavior is
         undefined. If part of a program tests floating-point status flags, sets floating-point control
         modes, or runs under non-default mode settings, but was translated with the state for the
         FENV_ACCESS pragma ‘‘off’’, the behavior is undefined. The default state (‘‘on’’ or
         ‘‘off’’) for the pragma is implementation-defined. (When execution passes from a part of
         the program translated with FENV_ACCESS ‘‘off’’ to a part translated with
         FENV_ACCESS ‘‘on’’, the state of the floating-point status flags is unspecified and the
         floating-point control modes have their default settings.)

    Footnote 213) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
              tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
              folding). In general, if the state of FENV_ACCESS is ‘‘off’’, the translator can assume that default
              modes are in effect and the flags are not tested.

    3   EXAMPLE
                #include <fenv.h>
                void f(double x)
                {
                      #pragma STDC FENV_ACCESS ON
                      void g(double);
                      void h(double);
                      /* ... */
                      g(x + 1);
                      h(x + 1);
                      /* ... */
                }

    4   If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
        x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
        contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.[214]

    Footnote 214) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
             hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is
             ‘‘off’’, just one evaluation of x + 1 would suffice.

### 7.6.2 [Floating-point exceptions]

    1   The following functions provide access to the floating-point status flags.[215] The int
        input argument for the functions represents a subset of floating-point exceptions, and can
        be zero or the bitwise OR of one or more floating-point exception macros, for example
        FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
        functions is undefined.

    Footnote 215) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
             abstraction of flags that are either set or clear. An implementation may endow floating-point status
             flags with more information — for example, the address of the code which first raised the floating-
             point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
             content of flags.

### 7.6.2.1 [The feclearexcept function]

    1 Synopsis
               #include <fenv.h>
                int feclearexcept(int excepts);
        Description

    2   The feclearexcept function attempts to clear the supported floating-point exceptions
        represented by its argument.
        Returns

    3   The feclearexcept function returns zero if the excepts argument is zero or if all
        the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.

### 7.6.2.2 [The fegetexceptflag function]

    1 Synopsis
                #include <fenv.h>
                 int fegetexceptflag(fexcept_t *flagp,
                      int excepts);
        Description

    2   The fegetexceptflag function attempts to store an implementation-defined
        representation of the states of the floating-point status flags indicated by the argument
        excepts in the object pointed to by the argument flagp.
        Returns

    3   The fegetexceptflag function returns zero if the representation was successfully
        stored. Otherwise, it returns a nonzero value.

### 7.6.2.3 [The feraiseexcept function]

    1 Synopsis
                #include <fenv.h>
                 int feraiseexcept(int excepts);
        Description

    2   The feraiseexcept function attempts to raise the supported floating-point exceptions
        represented by its argument.[216] The order in which these floating-point exceptions are
        raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
        additionally raises the ‘‘inexact’’ floating-point exception whenever it raises the
        ‘‘overflow’’ or ‘‘underflow’’ floating-point exception is implementation-defined.
        Returns

    Footnote 216) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
             Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
             in F.8.6 is in the same spirit.

    3   The feraiseexcept function returns zero if the excepts argument is zero or if all
        the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.

### 7.6.2.4 [The fesetexceptflag function]

    1 Synopsis
                #include <fenv.h>
                 int fesetexceptflag(const fexcept_t *flagp,
                      int excepts);
        Description

    2   The fesetexceptflag function attempts to set the floating-point status flags
        indicated by the argument excepts to the states stored in the object pointed to by
        flagp. The value of *flagp shall have been set by a previous call to
        fegetexceptflag whose second argument represented at least those floating-point
        exceptions represented by the argument excepts. This function does not raise floating-
        point exceptions, but only sets the state of the flags.
        Returns

    3   The fesetexceptflag function returns zero if the excepts argument is zero or if
        all the specified flags were successfully set to the appropriate state. Otherwise, it returns
        a nonzero value.

### 7.6.2.5 [The fetestexcept function]

    1 Synopsis
                #include <fenv.h>
                 int fetestexcept(int excepts);
        Description

    2   The fetestexcept function determines which of a specified subset of the floating-
        point exception flags are currently set. The excepts argument specifies the floating-
        point status flags to be queried.[217]
        Returns

    Footnote 217) This mechanism allows testing several floating-point exceptions with just one function call.

    3   The fetestexcept function returns the value of the bitwise OR of the floating-point
        exception macros corresponding to the currently set floating-point exceptions included in
        excepts.

    4   EXAMPLE       Call f if ‘‘invalid’’ is set, then g if ‘‘overflow’’ is set:
               #include <fenv.h>
               /* ... */
               {
                       #pragma STDC FENV_ACCESS ON
                       int set_excepts;
                       feclearexcept(FE_INVALID | FE_OVERFLOW);
                       // maybe raise exceptions
                       set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
                       if (set_excepts & FE_INVALID) f();
                       if (set_excepts & FE_OVERFLOW) g();
                       /* ... */
               }

### 7.6.3 [Rounding]

    1   The fegetround and fesetround functions provide control of rounding direction
        modes.

### 7.6.3.1 [The fegetround function]

    1 Synopsis
              #include <fenv.h>
               int fegetround(void);
        Description

    2   The fegetround function gets the current rounding direction.
        Returns

    3   The fegetround function returns the value of the rounding direction macro
        representing the current rounding direction or a negative value if there is no such
        rounding direction macro or the current rounding direction is not determinable.

### 7.6.3.2 [The fesetround function]

    1 Synopsis
              #include <fenv.h>
               int fesetround(int round);
        Description

    2   The fesetround function establishes the rounding direction represented by its
        argument round. If the argument is not equal to the value of a rounding direction macro,
        the rounding direction is not changed.
        Returns

    3   The fesetround function returns zero if and only if the requested rounding direction
        was established.

    4   EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the
        rounding direction fails.
               #include <fenv.h>
               #include <assert.h>
               void f(int round_dir)
               {
                     #pragma STDC FENV_ACCESS ON
                     int save_round;
                     int setround_ok;
                     save_round = fegetround();
                     setround_ok = fesetround(round_dir);
                     assert(setround_ok == 0);
                     /* ... */
                     fesetround(save_round);
                     /* ... */
               }

### 7.6.4 [Environment]

    1   The functions in this section manage the floating-point environment — status flags and
        control modes — as one entity.

### 7.6.4.1 [The fegetenv function]

    1 Synopsis
              #include <fenv.h>
               int fegetenv(fenv_t *envp);
        Description

    2   The fegetenv function attempts to store the current floating-point environment in the
        object pointed to by envp.
        Returns

    3   The fegetenv function returns zero if the environment was successfully stored.
        Otherwise, it returns a nonzero value.

### 7.6.4.2 [The feholdexcept function]

    1 Synopsis
              #include <fenv.h>
               int feholdexcept(fenv_t *envp);
        Description

    2   The feholdexcept function saves the current floating-point environment in the object
        pointed to by envp, clears the floating-point status flags, and then installs a non-stop
        (continue on floating-point exceptions) mode, if available, for all floating-point
        exceptions.[218]
        Returns

    Footnote 218) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
             handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
             such systems, the feholdexcept function can be used in conjunction with the feupdateenv
             function to write routines that hide spurious floating-point exceptions from their callers.

    3   The feholdexcept function returns zero if and only if non-stop floating-point
        exception handling was successfully installed.

### 7.6.4.3 [The fesetenv function]

    1 Synopsis
               #include <fenv.h>
                int fesetenv(const fenv_t *envp);
        Description

    2   The fesetenv function attempts to establish the floating-point environment represented
        by the object pointed to by envp. The argument envp shall point to an object set by a
        call to fegetenv or feholdexcept, or equal a floating-point environment macro.
        Note that fesetenv merely installs the state of the floating-point status flags
        represented through its argument, and does not raise these floating-point exceptions.
        Returns

    3   The fesetenv function returns zero if the environment was successfully established.
        Otherwise, it returns a nonzero value.

### 7.6.4.4 [The feupdateenv function]

    1 Synopsis
               #include <fenv.h>
                int feupdateenv(const fenv_t *envp);
        Description

    2   The feupdateenv function attempts to save the currently raised floating-point
        exceptions in its automatic storage, install the floating-point environment represented by
        the object pointed to by envp, and then raise the saved floating-point exceptions. The
        argument envp shall point to an object set by a call to feholdexcept or fegetenv,
        or equal a floating-point environment macro.
        Returns

    3   The feupdateenv function returns zero if all the actions were successfully carried out.
        Otherwise, it returns a nonzero value.

    4   EXAMPLE   Hide spurious underflow floating-point exceptions:
             #include <fenv.h>
             double f(double x)
             {
                   #pragma STDC FENV_ACCESS ON
                   double result;
                   fenv_t save_env;
                   if (feholdexcept(&save_env))
                         return /* indication of an environmental problem */;
                   // compute result
                   if (/* test spurious underflow */)
                         if (feclearexcept(FE_UNDERFLOW))
                                  return /* indication of an environmental problem */;
                   if (feupdateenv(&save_env))
                         return /* indication of an environmental problem */;
                   return result;
             }

### 7.7 [Characteristics of floating types <float.h>]

    1   The header <float.h> defines several macros that expand to various limits and
        parameters of the standard floating-point types.

    2   The macros, their meanings, and the constraints (or restrictions) on their values are listed
        in 5.2.4.2.2.

### 7.8 [Format conversion of integer types <inttypes.h>]

    1   The header <inttypes.h> includes the header <stdint.h> and extends it with
        additional facilities provided by hosted implementations.

    2   It declares functions for manipulating greatest-width integers and converting numeric
        character strings to greatest-width integers, and it declares the type
                 imaxdiv_t
        which is a structure type that is the type of the value returned by the imaxdiv function.
        For each type declared in <stdint.h>, it defines corresponding macros for conversion
        specifiers for use with the formatted input/output functions.[219]
        Forward references: integer types <stdint.h> (7.20), formatted input/output
        functions (7.21.6), formatted wide character input/output functions (7.29.2).

    Footnote 219) See ‘‘future library directions’’ (7.31.5).

### 7.8.1 [Macros for format specifiers]

    1   Each of the following object-like macros expands to a character string literal containing a
        conversion specifier, possibly modified by a length modifier, suitable for use within the
        format argument of a formatted input/output function when converting the corresponding
        integer type. These macro names have the general form of PRI (character string literals
        for the fprintf and fwprintf family) or SCN (character string literals for the
        fscanf and fwscanf family),[220] followed by the conversion specifier, followed by a
        name corresponding to a similar type name in 7.20.1. In these names, N represents the
        width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
        format string to print the value of an integer of type int_fast32_t.

    Footnote 220) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
             different format specifiers may be required for fprintf and fscanf, even when the type is the
             same.

    2   The fprintf macros for signed integers are:
               PRIdN             PRIdLEASTN                PRIdFASTN          PRIdMAX             PRIdPTR
               PRIiN             PRIiLEASTN                PRIiFASTN          PRIiMAX             PRIiPTR

    3   The fprintf macros for unsigned integers are:
               PRIoN             PRIoLEASTN                PRIoFASTN          PRIoMAX             PRIoPTR
               PRIuN             PRIuLEASTN                PRIuFASTN          PRIuMAX             PRIuPTR
               PRIxN             PRIxLEASTN                PRIxFASTN          PRIxMAX             PRIxPTR
               PRIXN             PRIXLEASTN                PRIXFASTN          PRIXMAX             PRIXPTR

    4   The fscanf macros for signed integers are:
               SCNdN           SCNdLEASTN               SCNdFASTN              SCNdMAX             SCNdPTR
               SCNiN           SCNiLEASTN               SCNiFASTN              SCNiMAX             SCNiPTR

    5   The fscanf macros for unsigned integers are:
               SCNoN           SCNoLEASTN               SCNoFASTN              SCNoMAX             SCNoPTR
               SCNuN           SCNuLEASTN               SCNuFASTN              SCNuMAX             SCNuPTR
               SCNxN           SCNxLEASTN               SCNxFASTN              SCNxMAX             SCNxPTR

    6   For each type that the implementation provides in <stdint.h>, the corresponding
        fprintf macros shall be defined and the corresponding fscanf macros shall be
        defined unless the implementation does not have a suitable fscanf length modifier for
        the type.

    7   EXAMPLE
                #include <inttypes.h>
                #include <wchar.h>
                int main(void)
                {
                      uintmax_t i = UINTMAX_MAX;    // this type always exists
                      wprintf(L"The largest integer value is %020"
                            PRIxMAX "\n", i);
                      return 0;
                }

### 7.8.2 [Functions for greatest-width integer types]

### 7.8.2.1 [The imaxabs function]

    1 Synopsis
               #include <inttypes.h>
                intmax_t imaxabs(intmax_t j);
        Description

    2   The imaxabs function computes the absolute value of an integer j. If the result cannot
        be represented, the behavior is undefined.[221]
        Returns

    Footnote 221) The absolute value of the most negative number cannot be represented in two’s complement.

    3   The imaxabs function returns the absolute value.

### 7.8.2.2 [The imaxdiv function]

    1 Synopsis
              #include <inttypes.h>
               imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
        Description

    2   The imaxdiv function computes numer / denom and numer % denom in a single
        operation.
        Returns

    3   The imaxdiv function returns a structure of type imaxdiv_t comprising both the
        quotient and the remainder. The structure shall contain (in either order) the members
        quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
        either part of the result cannot be represented, the behavior is undefined.

### 7.8.2.3 [The strtoimax and strtoumax functions]

    1 Synopsis
              #include <inttypes.h>
               intmax_t strtoimax(const char * restrict nptr,
                    char ** restrict endptr, int base);
               uintmax_t strtoumax(const char * restrict nptr,
                    char ** restrict endptr, int base);
        Description

    2   The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
        strtoul, and strtoull functions, except that the initial portion of the string is
        converted to intmax_t and uintmax_t representation, respectively.
        Returns

    3   The strtoimax and strtoumax functions return the converted value, if any. If no
        conversion could be performed, zero is returned. If the correct value is outside the range
        of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
        (according to the return type and sign of the value, if any), and the value of the macro
        ERANGE is stored in errno.
        Forward references: the strtol, strtoll, strtoul, and strtoull functions
        (7.22.1.4).

### 7.8.2.4 [The wcstoimax and wcstoumax functions]

    1 Synopsis
              #include <stddef.h>           // for wchar_t
               #include <inttypes.h>
               intmax_t wcstoimax(const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr, int base);
               uintmax_t wcstoumax(const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr, int base);
        Description

    2   The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
        wcstoul, and wcstoull functions except that the initial portion of the wide string is
        converted to intmax_t and uintmax_t representation, respectively.
        Returns

    3   The wcstoimax function returns the converted value, if any. If no conversion could be
        performed, zero is returned. If the correct value is outside the range of representable
        values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
        return type and sign of the value, if any), and the value of the macro ERANGE is stored in
        errno.
        Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
        (7.29.4.1.2).

### 7.9 [Alternative spellings <iso646.h>]

    1   The header <iso646.h> defines the following eleven macros (on the left) that expand
        to the corresponding tokens (on the right):
              and          &&
              and_eq       &=
              bitand       &
              bitor        |
              compl        ~
              not          !
              not_eq       !=
              or           ||
              or_eq        |=
              xor          ^
              xor_eq       ^=

### 7.10 [Sizes of integer types <limits.h>]

    1   The header <limits.h> defines several macros that expand to various limits and
        parameters of the standard integer types.

    2   The macros, their meanings, and the constraints (or restrictions) on their values are listed
        in 5.2.4.2.1.

### 7.11 [Localization <locale.h>]

    1   The header <locale.h> declares two functions, one type, and defines several macros.

    2   The type is
               struct lconv
        which contains members related to the formatting of numeric values. The structure shall
        contain at least the following members, in any order. The semantics of the members and
        their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
        the values specified in the comments.
               char *decimal_point;                   // "."
               char *thousands_sep;                   // ""
               char *grouping;                        // ""
               char *mon_decimal_point;               // ""
               char *mon_thousands_sep;               // ""
               char *mon_grouping;                    // ""
               char *positive_sign;                   // ""
               char *negative_sign;                   // ""
               char *currency_symbol;                 // ""
               char frac_digits;                      // CHAR_MAX
               char p_cs_precedes;                    // CHAR_MAX
               char n_cs_precedes;                    // CHAR_MAX
               char p_sep_by_space;                   // CHAR_MAX
               char n_sep_by_space;                   // CHAR_MAX
               char p_sign_posn;                      // CHAR_MAX
               char n_sign_posn;                      // CHAR_MAX
               char *int_curr_symbol;                 // ""
               char int_frac_digits;                  // CHAR_MAX
               char int_p_cs_precedes;                // CHAR_MAX
               char int_n_cs_precedes;                // CHAR_MAX
               char int_p_sep_by_space;               // CHAR_MAX
               char int_n_sep_by_space;               // CHAR_MAX
               char int_p_sign_posn;                  // CHAR_MAX
               char int_n_sign_posn;                  // CHAR_MAX

    3   The macros defined are NULL (described in 7.19); and
                 LC_ALL
                 LC_COLLATE
                 LC_CTYPE
                 LC_MONETARY
                 LC_NUMERIC
                 LC_TIME
        which expand to integer constant expressions with distinct values, suitable for use as the
        first argument to the setlocale function.[222] Additional macro definitions, beginning
        with the characters LC_ and an uppercase letter,[223] may also be specified by the
        implementation.

    Footnote 222) ISO/IEC 9945−2 specifies locale and charmap formats that may be used to specify locales for C.

    Footnote 223) See ‘‘future library directions’’ (7.31.6).

### 7.11.1 [Locale control]

### 7.11.1.1 [The setlocale function]

    1 Synopsis
                #include <locale.h>
                 char *setlocale(int category, const char *locale);
        Description

    2   The setlocale function selects the appropriate portion of the program’s locale as
        specified by the category and locale arguments. The setlocale function may be
        used to change or query the program’s entire current locale or portions thereof. The value
        LC_ALL for category names the program’s entire locale; the other values for
        category name only a portion of the program’s locale. LC_COLLATE affects the
        behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
        the character handling functions[224] and the multibyte and wide character functions.
        LC_MONETARY affects the monetary formatting information returned by the
        localeconv function. LC_NUMERIC affects the decimal-point character for the
        formatted input/output functions and the string conversion functions, as well as the
        nonmonetary formatting information returned by the localeconv function. LC_TIME
        affects the behavior of the strftime and wcsftime functions.

    Footnote 224) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
             isxdigit.

    3   A value of "C" for locale specifies the minimal environment for C translation; a value
        of "" for locale specifies the locale-specific native environment. Other
        implementation-defined strings may be passed as the second argument to setlocale.

    4   At program startup, the equivalent of
                setlocale(LC_ALL, "C");
        is executed.

    5   A call to the setlocale function may introduce a data race with other calls to the
        setlocale function or with calls to functions that are affected by the current locale.
        The implementation shall behave as if no library function calls the setlocale function.
        Returns

    6   If a pointer to a string is given for locale and the selection can be honored, the
        setlocale function returns a pointer to the string associated with the specified
        category for the new locale. If the selection cannot be honored, the setlocale
        function returns a null pointer and the program’s locale is not changed.

    7   A null pointer for locale causes the setlocale function to return a pointer to the
        string associated with the category for the program’s current locale; the program’s
        locale is not changed.[225]

    Footnote 225) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
             locale when category has the value LC_ALL.

    8   The pointer to string returned by the setlocale function is such that a subsequent call
        with that string value and its associated category will restore that part of the program’s
        locale. The string pointed to shall not be modified by the program, but may be
        overwritten by a subsequent call to the setlocale function.
        Forward references: formatted input/output functions (7.21.6), multibyte/wide
        character conversion functions (7.22.7), multibyte/wide string conversion functions
        (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.24.4.3), the
        strftime function (7.27.3.5), the strxfrm function (7.24.4.5).

### 7.11.2 [Numeric formatting convention inquiry]

### 7.11.2.1 [The localeconv function]

    1 Synopsis
               #include <locale.h>
                struct lconv *localeconv(void);
        Description

    2   The localeconv function sets the components of an object with type struct lconv
        with values appropriate for the formatting of numeric quantities (monetary and otherwise)
        according to the rules of the current locale.

    3   The members of the structure with type char * are pointers to strings, any of which
        (except decimal_point) can point to "", to indicate that the value is not available in
        the current locale or is of zero length. Apart from grouping and mon_grouping, the
        strings shall start and end in the initial shift state. The members with type char are
        nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
        available in the current locale. The members include the following:
        char *decimal_point
                  The decimal-point character used to format nonmonetary quantities.
        char *thousands_sep
                  The character used to separate groups of digits before the decimal-point
                  character in formatted nonmonetary quantities.
        char *grouping
                  A string whose elements indicate the size of each group of digits in
                  formatted nonmonetary quantities.
        char *mon_decimal_point
                  The decimal-point used to format monetary quantities.
        char *mon_thousands_sep
                  The separator for groups of digits before the decimal-point in formatted
                  monetary quantities.
        char *mon_grouping
                  A string whose elements indicate the size of each group of digits in
                  formatted monetary quantities.
        char *positive_sign
                  The string used to indicate a nonnegative-valued formatted monetary
                  quantity.
        char *negative_sign
                  The string used to indicate a negative-valued formatted monetary quantity.
        char *currency_symbol
                  The local currency symbol applicable to the current locale.
        char frac_digits
                  The number of fractional digits (those after the decimal-point) to be
                  displayed in a locally formatted monetary quantity.
        char p_cs_precedes
                  Set to 1 or 0 if the currency_symbol respectively precedes or
                  succeeds the value for a nonnegative locally formatted monetary quantity.
    char n_cs_precedes
              Set to 1 or 0 if the currency_symbol respectively precedes or
              succeeds the value for a negative locally formatted monetary quantity.
    char p_sep_by_space
              Set to a value indicating the separation of the currency_symbol, the
              sign string, and the value for a nonnegative locally formatted monetary
              quantity.
    char n_sep_by_space
              Set to a value indicating the separation of the currency_symbol, the
              sign string, and the value for a negative locally formatted monetary
              quantity.
    char p_sign_posn
              Set to a value indicating the positioning of the positive_sign for a
              nonnegative locally formatted monetary quantity.
    char n_sign_posn
              Set to a value indicating the positioning of the negative_sign for a
              negative locally formatted monetary quantity.
    char *int_curr_symbol
              The international currency symbol applicable to the current locale. The
              first three characters contain the alphabetic international currency symbol
              in accordance with those specified in ISO 4217. The fourth character
              (immediately preceding the null character) is the character used to separate
              the international currency symbol from the monetary quantity.
    char int_frac_digits
              The number of fractional digits (those after the decimal-point) to be
              displayed in an internationally formatted monetary quantity.
    char int_p_cs_precedes
              Set to 1 or 0 if the int_curr_symbol respectively precedes or
              succeeds the value for a nonnegative internationally formatted monetary
              quantity.
    char int_n_cs_precedes
              Set to 1 or 0 if the int_curr_symbol respectively precedes or
              succeeds the value for a negative internationally formatted monetary
              quantity.
    char int_p_sep_by_space
              Set to a value indicating the separation of the int_curr_symbol, the
              sign string, and the value for a nonnegative internationally formatted
              monetary quantity.
        char int_n_sep_by_space
                  Set to a value indicating the separation of the int_curr_symbol, the
                  sign string, and the value for a negative internationally formatted monetary
                  quantity.
        char int_p_sign_posn
                  Set to a value indicating the positioning of the positive_sign for a
                  nonnegative internationally formatted monetary quantity.
        char int_n_sign_posn
                  Set to a value indicating the positioning of the negative_sign for a
                  negative internationally formatted monetary quantity.

    4   The elements of grouping and mon_grouping are interpreted according to the
        following:
        CHAR_MAX      No further grouping is to be performed.
        0             The previous element is to be repeatedly used for the remainder of the
                      digits.
        other         The integer value is the number of digits that compose the current group.
                      The next element is examined to determine the size of the next group of
                      digits before the current group.

    5   The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
        and int_n_sep_by_space are interpreted according to the following:
        0   No space separates the currency symbol and value.
        1   If the currency symbol and sign string are adjacent, a space separates them from the
            value; otherwise, a space separates the currency symbol from the value.
        2   If the currency symbol and sign string are adjacent, a space separates them;
            otherwise, a space separates the sign string from the value.
        For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
        int_curr_symbol is used instead of a space.

    6   The values of p_sign_posn, n_sign_posn, int_p_sign_posn,                            and
        int_n_sign_posn are interpreted according to the following:
        0   Parentheses surround the quantity and currency symbol.
        1   The sign string precedes the quantity and currency symbol.
        2   The sign string succeeds the quantity and currency symbol.
        3   The sign string immediately precedes the currency symbol.
        4   The sign string immediately succeeds the currency symbol.

    7    The implementation shall behave as if no library function calls the localeconv
         function.
         Returns

    8    The localeconv function returns a pointer to the filled-in object. The structure
         pointed to by the return value shall not be modified by the program, but may be
         overwritten by a subsequent call to the localeconv function. In addition, calls to the
         setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
         overwrite the contents of the structure.

    9    EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
         monetary quantities.
                                       Local format                                  International format

         Country            Positive                  Negative                 Positive               Negative

         Country1     1.234,56 mk             -1.234,56 mk                  FIM 1.234,56        FIM -1.234,56
         Country2     L.1.234                 -L.1.234                      ITL 1.234           -ITL 1.234
         Country3     ƒ 1.234,56              ƒ -1.234,56                   NLG 1.234,56        NLG -1.234,56
         Country4     SFrs.1,234.56           SFrs.1,234.56C                CHF 1,234.56        CHF 1,234.56C

    10   For these four countries, the respective values for the monetary members of the structure returned by
         localeconv could be:
                                           Country1              Country2           Country3            Country4

         mon_decimal_point                 ","                   ""                ","                 "."
         mon_thousands_sep                 "."                   "."               "."                 ","
         mon_grouping                      "\3"                  "\3"              "\3"                "\3"
         positive_sign                     ""                    ""                ""                  ""
         negative_sign                     "-"                   "-"               "-"                 "C"
         currency_symbol                   "mk"                  "L."              "\u0192"            "SFrs."
         frac_digits                       2                     0                 2                   2
         p_cs_precedes                     0                     1                 1                   1
         n_cs_precedes                     0                     1                 1                   1
         p_sep_by_space                    1                     0                 1                   0
         n_sep_by_space                    1                     0                 2                   0
         p_sign_posn                       1                     1                 1                   1
         n_sign_posn                       1                     1                 4                   2
         int_curr_symbol                   "FIM "                "ITL "            "NLG "              "CHF "
         int_frac_digits                   2                     0                 2                   2
         int_p_cs_precedes                 1                     1                 1                   1
         int_n_cs_precedes                 1                     1                 1                   1
         int_p_sep_by_space                1                     1                 1                   1
         int_n_sep_by_space                2                     1                 2                   1
         int_p_sign_posn                   1                     1                 1                   1
         int_n_sign_posn                   4                     1                 4                   2

    11   EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
         affect the formatted value.
                                                                       p_sep_by_space

         p_cs_precedes           p_sign_posn                0                   1                  2

                         0                    0         (1.25$)            (1.25 $)            (1.25$)
                                              1         +1.25$             +1.25 $             + 1.25$
                                              2         1.25$+             1.25 $+             1.25$ +
                                              3         1.25+$             1.25 +$             1.25+ $
                                              4         1.25$+             1.25 $+             1.25$ +

                         1                    0         ($1.25)            ($ 1.25)            ($1.25)
                                              1         +$1.25             +$ 1.25             + $1.25
                                              2         $1.25+             $ 1.25+             $1.25 +
                                              3         +$1.25             +$ 1.25             + $1.25
                                              4         $+1.25             $+ 1.25             $ +1.25

### 7.12 [Mathematics <math.h>]

    1   The header <math.h> declares two types and many mathematical functions and defines
        several macros. Most synopses specify a family of functions consisting of a principal
        function with one or more double parameters, a double return value, or both; and
        other functions with the same name but with f and l suffixes, which are corresponding
        functions with float and long double parameters, return values, or both.[226]
        Integer arithmetic functions and conversion functions are discussed later.

    Footnote 226) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
             and return values in wider format than the synopsis prototype indicates.

    2   The types
                float_t
                double_t
        are floating types at least as wide as float and double, respectively, and such that
        double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
        float_t and double_t are float and double, respectively; if
        FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
        2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
        otherwise implementation-defined.[227]

    Footnote 227) The types float_t and double_t are intended to be the implementation’s most efficient types at
             least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the
             type float_t is the narrowest type used by the implementation to evaluate floating expressions.

    3   The macro
                HUGE_VAL
        expands to a positive double constant expression, not necessarily representable as a
        float. The macros
                HUGE_VALF
                HUGE_VALL
        are respectively float and long double analogs of HUGE_VAL.[228]

    Footnote 228) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
             supports infinities.

    4   The macro
                INFINITY
        expands to a constant expression of type float representing positive or unsigned
        infinity, if available; else to a positive constant of type float that overflows at
        translation time.[229]

    Footnote 229) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.

    5   The macro
                 NAN
        is defined if and only if the implementation supports quiet NaNs for the float type. It
        expands to a constant expression of type float representing a quiet NaN.

    6   The number classification macros
                 FP_INFINITE
                 FP_NAN
                 FP_NORMAL
                 FP_SUBNORMAL
                 FP_ZERO
        represent the mutually exclusive kinds of floating-point values. They expand to integer
        constant expressions with distinct values. Additional implementation-defined floating-
        point classifications, with macro definitions beginning with FP_ and an uppercase letter,
        may also be specified by the implementation.

    7   The macro
                 FP_FAST_FMA
        is optionally defined. If defined, it indicates that the fma function generally executes
        about as fast as, or faster than, a multiply and an add of double operands.[230] The
        macros
                 FP_FAST_FMAF
                 FP_FAST_FMAL
        are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
        these macros expand to the integer constant 1.

    Footnote 230) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
             directly with a hardware multiply-add instruction. Software implementations are expected to be
             substantially slower.

    8   The macros
                 FP_ILOGB0
                 FP_ILOGBNAN
        expand to integer constant expressions whose values are returned by ilogb(x) if x is
        zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
        -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.

    9   The macros
                MATH_ERRNO
                MATH_ERREXCEPT
        expand to the integer constants 1 and 2, respectively; the macro
                math_errhandling
        expands to an expression that has type int and the value MATH_ERRNO,
        MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
        constant for the duration of the program. It is unspecified whether
        math_errhandling is a macro or an identifier with external linkage. If a macro
        definition is suppressed or a program defines an identifier with the name
        math_errhandling, the behavior is undefined.              If the expression
        math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
        shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
        <fenv.h>.

### 7.12.1 [Treatment of error conditions]

    1   The behavior of each of the functions in <math.h> is specified for all representable
        values of its input arguments, except where stated otherwise. Each function shall execute
        as if it were a single operation without raising SIGFPE and without generating any of the
        floating-point exceptions ‘‘invalid’’, ‘‘divide-by-zero’’, or ‘‘overflow’’ except to reflect
        the result of the function.

    2   For all functions, a domain error occurs if an input argument is outside the domain over
        which the mathematical function is defined. The description of each function lists any
        required domain errors; an implementation may define additional domain errors, provided
        that such errors are consistent with the mathematical definition of the function.[231] On a
        domain error, the function returns an implementation-defined value; if the integer
        expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
        errno acquires the value EDOM; if the integer expression math_errhandling &
        MATH_ERREXCEPT is nonzero, the ‘‘invalid’’ floating-point exception is raised.

    Footnote 231) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
             error if the mathematical domain of the function does not include the infinity.

    3   Similarly, a pole error (also known as a singularity or infinitary) occurs if the
        mathematical function has an exact infinite result as the finite input argument(s) are
        approached in the limit (for example, log(0.0)). The description of each function lists
        any required pole errors; an implementation may define additional pole errors, provided
        that such errors are consistent with the mathematical definition of the function. On a pole
        error, the function returns an implementation-defined value; if the integer expression
        math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
        acquires the value ERANGE; if the integer expression math_errhandling &
        MATH_ERREXCEPT is nonzero, the ‘‘divide-by-zero’’ floating-point exception is raised.

    4   Likewise, a range error occurs if the mathematical result of the function cannot be
        represented in an object of the specified type, due to extreme magnitude.

    5   A floating result overflows if the magnitude of the mathematical result is finite but so
        large that the mathematical result cannot be represented without extraordinary roundoff
        error in an object of the specified type. If a floating result overflows and default rounding
        is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or
        HUGE_VALL according to the return type, with the same sign as the correct value of the
        function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
        the integer expression errno acquires the value ERANGE; if the integer expression
        math_errhandling & MATH_ERREXCEPT is nonzero, the ‘‘overflow’’ floating-
        point exception is raised.

    6   The result underflows if the magnitude of the mathematical result is so small that the
        mathematical result cannot be represented, without extraordinary roundoff error, in an
        object of the specified type.[232] If the result underflows, the function returns an
        implementation-defined value whose magnitude is no greater than the smallest
        normalized positive number in the specified type; if the integer expression
        math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
        value     ERANGE       is    implementation-defined;     if   the integer  expression
        math_errhandling & MATH_ERREXCEPT is nonzero, whether the ‘‘underflow’’
        floating-point exception is raised is implementation-defined.

    Footnote 232) The term underflow here is intended to encompass both ‘‘gradual underflow’’ as in IEC 60559 and
             also ‘‘flush-to-zero’’ underflow.

    7   If a domain, pole, or range error occurs and the integer expression
        math_errhandling & MATH_ERRNO is zero,[233] then errno shall either be set to
        the value corresponding to the error or left unmodified. If no such error occurs, errno
        shall be left unmodified regardless of the setting of math_errhandling.

    Footnote 233) Math errors are being indicated by the floating-point exception flags rather than by errno.

### 7.12.2 [The FP_CONTRACT pragma]

    1 Synopsis
                #include <math.h>
                 #pragma STDC FP_CONTRACT on-off-switch
        Description

    2   The FP_CONTRACT pragma can be used to allow (if the state is ‘‘on’’) or disallow (if the
        state is ‘‘off’’) the implementation to contract expressions (6.5). Each pragma can occur
        either outside external declarations or preceding all explicit declarations and statements
        inside a compound statement. When outside external declarations, the pragma takes
        effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
        the end of the translation unit. When inside a compound statement, the pragma takes
        effect from its occurrence until another FP_CONTRACT pragma is encountered
        (including within a nested compound statement), or until the end of the compound
        statement; at the end of a compound statement the state for the pragma is restored to its
        condition just before the compound statement. If this pragma is used in any other
        context, the behavior is undefined. The default state (‘‘on’’ or ‘‘off’’) for the pragma is
        implementation-defined.

### 7.12.3 [Classification macros]

    1   In the synopses in this subclause, real-floating indicates that the argument shall be an
        expression of real floating type.

### 7.12.3.1 [The fpclassify macro]

    1 Synopsis
                #include <math.h>
                 int fpclassify(real-floating x);
        Description

    2   The fpclassify macro classifies its argument value as NaN, infinite, normal,
        subnormal, zero, or into another implementation-defined category. First, an argument
        represented in a format wider than its semantic type is converted to its semantic type.
        Then classification is based on the type of the argument.[234]
        Returns

    Footnote 234) Since an expression can be evaluated with more range and precision than its type has, it is important to
             know the type that classification is based on. For example, a normal long double value might
             become subnormal when converted to double, and zero when converted to float.

    3   The fpclassify macro returns the value of the number classification macro
        appropriate to the value of its argument.

### 7.12.3.2 [The isfinite macro]

    1 Synopsis
               #include <math.h>
                int isfinite(real-floating x);
        Description

    2   The isfinite macro determines whether its argument has a finite value (zero,
        subnormal, or normal, and not infinite or NaN). First, an argument represented in a
        format wider than its semantic type is converted to its semantic type. Then determination
        is based on the type of the argument.
        Returns

    3   The isfinite macro returns a nonzero value if and only if its argument has a finite
        value.

### 7.12.3.3 [The isinf macro]

    1 Synopsis
               #include <math.h>
                int isinf(real-floating x);
        Description

    2   The isinf macro determines whether its argument value is an infinity (positive or
        negative). First, an argument represented in a format wider than its semantic type is
        converted to its semantic type. Then determination is based on the type of the argument.
        Returns

    3   The isinf macro returns a nonzero value if and only if its argument has an infinite
        value.

### 7.12.3.4 [The isnan macro]

    1 Synopsis
               #include <math.h>
                int isnan(real-floating x);
        Description

    2   The isnan macro determines whether its argument value is a NaN. First, an argument
        represented in a format wider than its semantic type is converted to its semantic type.
        Then determination is based on the type of the argument.[235]
        Returns

    Footnote 235) For the isnan macro, the type for determination does not matter unless the implementation supports
             NaNs in the evaluation type but not in the semantic type.

    3   The isnan macro returns a nonzero value if and only if its argument has a NaN value.

### 7.12.3.5 [The isnormal macro]

    1 Synopsis
               #include <math.h>
                int isnormal(real-floating x);
        Description

    2   The isnormal macro determines whether its argument value is normal (neither zero,
        subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
        semantic type is converted to its semantic type. Then determination is based on the type
        of the argument.
        Returns

    3   The isnormal macro returns a nonzero value if and only if its argument has a normal
        value.

### 7.12.3.6 [The signbit macro]

    1 Synopsis
               #include <math.h>
                int signbit(real-floating x);
        Description

    2   The signbit macro determines whether the sign of its argument value is negative.[236]
        Returns

    Footnote 236) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
             unsigned, it is treated as positive.

    3   The signbit macro returns a nonzero value if and only if the sign of its argument value
        is negative.

### 7.12.4 [Trigonometric functions]

### 7.12.4.1 [The acos functions]

    1 Synopsis
              #include <math.h>
               double acos(double x);
               float acosf(float x);
               long double acosl(long double x);
        Description

    2   The acos functions compute the principal value of the arc cosine of x. A domain error
        occurs for arguments not in the interval [−1, +1].
        Returns

    3   The acos functions return arccos x in the interval [0, π ] radians.

### 7.12.4.2 [The asin functions]

    1 Synopsis
              #include <math.h>
               double asin(double x);
               float asinf(float x);
               long double asinl(long double x);
        Description

    2   The asin functions compute the principal value of the arc sine of x. A domain error
        occurs for arguments not in the interval [−1, +1].
        Returns

    3   The asin functions return arcsin x in the interval [−π /2, +π /2] radians.

### 7.12.4.3 [The atan functions]

    1 Synopsis
              #include <math.h>
               double atan(double x);
               float atanf(float x);
               long double atanl(long double x);
        Description

    2   The atan functions compute the principal value of the arc tangent of x.
        Returns

    3   The atan functions return arctan x in the interval [−π /2, +π /2] radians.

### 7.12.4.4 [The atan2 functions]

    1 Synopsis
              #include <math.h>
               double atan2(double y, double x);
               float atan2f(float y, float x);
               long double atan2l(long double y, long double x);
        Description

    2   The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
        arguments to determine the quadrant of the return value. A domain error may occur if
        both arguments are zero.
        Returns

    3   The atan2 functions return arctan y/x in the interval [−π , +π ] radians.

### 7.12.4.5 [The cos functions]

    1 Synopsis
              #include <math.h>
               double cos(double x);
               float cosf(float x);
               long double cosl(long double x);
        Description

    2   The cos functions compute the cosine of x (measured in radians).
        Returns

    3   The cos functions return cos x.

### 7.12.4.6 [The sin functions]

    1 Synopsis
              #include <math.h>
               double sin(double x);
               float sinf(float x);
               long double sinl(long double x);
        Description

    2   The sin functions compute the sine of x (measured in radians).
        Returns

    3   The sin functions return sin x.

### 7.12.4.7 [The tan functions]

    1 Synopsis
              #include <math.h>
               double tan(double x);
               float tanf(float x);
               long double tanl(long double x);
        Description

    2   The tan functions return the tangent of x (measured in radians).
        Returns

    3   The tan functions return tan x.

### 7.12.5 [Hyperbolic functions]

### 7.12.5.1 [The acosh functions]

    1 Synopsis
              #include <math.h>
               double acosh(double x);
               float acoshf(float x);
               long double acoshl(long double x);
        Description

    2   The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
        error occurs for arguments less than 1.
        Returns

    3   The acosh functions return arcosh x in the interval [0, +∞].

### 7.12.5.2 [The asinh functions]

    1 Synopsis
              #include <math.h>
               double asinh(double x);
               float asinhf(float x);
               long double asinhl(long double x);
        Description

    2   The asinh functions compute the arc hyperbolic sine of x.
        Returns

    3   The asinh functions return arsinh x.

### 7.12.5.3 [The atanh functions]

    1 Synopsis
              #include <math.h>
               double atanh(double x);
               float atanhf(float x);
               long double atanhl(long double x);
        Description

    2   The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
        for arguments not in the interval [−1, +1]. A pole error may occur if the argument equals
        −1 or +1.
        Returns

    3   The atanh functions return artanh x.

### 7.12.5.4 [The cosh functions]

    1 Synopsis
              #include <math.h>
               double cosh(double x);
               float coshf(float x);
               long double coshl(long double x);
        Description

    2   The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
        magnitude of x is too large.
        Returns

    3   The cosh functions return cosh x.

### 7.12.5.5 [The sinh functions]

    1 Synopsis
              #include <math.h>
               double sinh(double x);
               float sinhf(float x);
               long double sinhl(long double x);
        Description

    2   The sinh functions compute the hyperbolic sine of x. A range error occurs if the
        magnitude of x is too large.
        Returns

    3   The sinh functions return sinh x.

### 7.12.5.6 [The tanh functions]

    1 Synopsis
              #include <math.h>
               double tanh(double x);
               float tanhf(float x);
               long double tanhl(long double x);
        Description

    2   The tanh functions compute the hyperbolic tangent of x.
        Returns

    3   The tanh functions return tanh x.

### 7.12.6 [Exponential and logarithmic functions]

### 7.12.6.1 [The exp functions]

    1 Synopsis
              #include <math.h>
               double exp(double x);
               float expf(float x);
               long double expl(long double x);
        Description

    2   The exp functions compute the base-e exponential of x. A range error occurs if the
        magnitude of x is too large.
        Returns

    3   The exp functions return ex .

### 7.12.6.2 [The exp2 functions]

    1 Synopsis
              #include <math.h>
               double exp2(double x);
               float exp2f(float x);
               long double exp2l(long double x);
        Description

    2   The exp2 functions compute the base-2 exponential of x. A range error occurs if the
        magnitude of x is too large.
        Returns

    3   The exp2 functions return 2x .

### 7.12.6.3 [The expm1 functions]

    1 Synopsis
               #include <math.h>
                double expm1(double x);
                float expm1f(float x);
                long double expm1l(long double x);
        Description

    2   The expm1 functions compute the base-e exponential of the argument, minus 1. A range
        error occurs if x is too large.[237]
        Returns

    Footnote 237) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.

    3   The expm1 functions return ex − 1.

### 7.12.6.4 [The frexp functions]

    1 Synopsis
               #include <math.h>
                double frexp(double value, int *exp);
                float frexpf(float value, int *exp);
                long double frexpl(long double value, int *exp);
        Description

    2   The frexp functions break a floating-point number into a normalized fraction and an
        integral power of 2. They store the integer in the int object pointed to by exp.
        Returns

    3   If value is not a floating-point number or if the integral power of 2 is outside the range
        of int, the results are unspecified. Otherwise, the frexp functions return the value x,
        such that x has a magnitude in the interval [1/2, [1] or zero, and value equals x × 2*exp .
        If value is zero, both parts of the result are zero.

    Footnote 1) This International Standard is designed to promote the portability of C programs among a variety of
             data-processing systems. It is intended for use by implementors and programmers.

### 7.12.6.5 [The ilogb functions]

    1 Synopsis
              #include <math.h>
               int ilogb(double x);
               int ilogbf(float x);
               int ilogbl(long double x);
        Description

    2   The ilogb functions extract the exponent of x as a signed int value. If x is zero they
        compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
        a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
        the corresponding logb function and casting the returned value to type int. A domain
        error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
        the range of the return type, the numeric result is unspecified.
        Returns

    3   The ilogb functions return the exponent of x as a signed int value.
        Forward references: the logb functions (7.12.6.11).

### 7.12.6.6 [The ldexp functions]

    1 Synopsis
              #include <math.h>
               double ldexp(double x, int exp);
               float ldexpf(float x, int exp);
               long double ldexpl(long double x, int exp);
        Description

    2   The ldexp functions multiply a floating-point number by an integral power of 2. A
        range error may occur.
        Returns

    3   The ldexp functions return x × 2exp .

### 7.12.6.7 [The log functions]

    1 Synopsis
              #include <math.h>
               double log(double x);
               float logf(float x);
               long double logl(long double x);
        Description

    2   The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
        the argument is negative. A pole error may occur if the argument is zero.
        Returns

    3   The log functions return loge x.

### 7.12.6.8 [The log10 functions]

    1 Synopsis
               #include <math.h>
                double log10(double x);
                float log10f(float x);
                long double log10l(long double x);
        Description

    2   The log10 functions compute the base-10 (common) logarithm of x. A domain error
        occurs if the argument is negative. A pole error may occur if the argument is zero.
        Returns

    3   The log10 functions return log10 x.

### 7.12.6.9 [The log1p functions]

    1 Synopsis
               #include <math.h>
                double log1p(double x);
                float log1pf(float x);
                long double log1pl(long double x);
        Description

    2   The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.[238]
        A domain error occurs if the argument is less than −1. A pole error may occur if the
        argument equals −1.
        Returns

    Footnote 238) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).

    3   The log1p functions return loge (1 + x).

### 7.12.6.10 [The log2 functions]

    1 Synopsis
              #include <math.h>
               double log2(double x);
               float log2f(float x);
               long double log2l(long double x);
        Description

    2   The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
        argument is less than zero. A pole error may occur if the argument is zero.
        Returns

    3   The log2 functions return log2 x.

### 7.12.6.11 [The logb functions]

    1 Synopsis
              #include <math.h>
               double logb(double x);
               float logbf(float x);
               long double logbl(long double x);
        Description

    2   The logb functions extract the exponent of x, as a signed integer value in floating-point
        format. If x is subnormal it is treated as though it were normalized; thus, for positive
        finite x,
              1 ≤ x × FLT_RADIX−logb(x) < FLT_RADIX
        A domain error or pole error may occur if the argument is zero.
        Returns

    3   The logb functions return the signed exponent of x.

### 7.12.6.12 [The modf functions]

    1 Synopsis
              #include <math.h>
               double modf(double value, double *iptr);
               float modff(float value, float *iptr);
               long double modfl(long double value, long double *iptr);
        Description

    2   The modf functions break the argument value into integral and fractional parts, each of
        which has the same type and sign as the argument. They store the integral part (in
        floating-point format) in the object pointed to by iptr.
        Returns

    3   The modf functions return the signed fractional part of value.

### 7.12.6.13 [The scalbn and scalbln functions]

    1 Synopsis
              #include <math.h>
               double scalbn(double x, int n);
               float scalbnf(float x, int n);
               long double scalbnl(long double x, int n);
               double scalbln(double x, long int n);
               float scalblnf(float x, long int n);
               long double scalblnl(long double x, long int n);
        Description

    2   The scalbn and scalbln functions compute x × FLT_RADIXn efficiently, not
        normally by computing FLT_RADIXn explicitly. A range error may occur.
        Returns

    3   The scalbn and scalbln functions return x × FLT_RADIXn .

### 7.12.7 [Power and absolute-value functions]

### 7.12.7.1 [The cbrt functions]

    1 Synopsis
              #include <math.h>
               double cbrt(double x);
               float cbrtf(float x);
               long double cbrtl(long double x);
        Description

    2   The cbrt functions compute the real cube root of x.
        Returns

    3   The cbrt functions return x1/3 .

### 7.12.7.2 [The fabs functions]

    1 Synopsis
              #include <math.h>
               double fabs(double x);
               float fabsf(float x);
               long double fabsl(long double x);
        Description

    2   The fabs functions compute the absolute value of a floating-point number x.
        Returns

    3   The fabs functions return | x |.

### 7.12.7.3 [The hypot functions]

    1 Synopsis
              #include <math.h>
               double hypot(double x, double y);
               float hypotf(float x, float y);
               long double hypotl(long double x, long double y);
        Description

    2   The hypot functions compute the square root of the sum of the squares of x and y,
        without undue overflow or underflow. A range error may occur.

    3   Returns

    4   The hypot functions return √
                                   ⎯⎯⎯⎯⎯⎯
                                     x2 + y 2 .

### 7.12.7.4 [The pow functions]

    1 Synopsis
              #include <math.h>
               double pow(double x, double y);
               float powf(float x, float y);
               long double powl(long double x, long double y);
        Description

    2   The pow functions compute x raised to the power y. A domain error occurs if x is finite
        and negative and y is finite and not an integer value. A range error may occur. A domain
        error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
        zero and y is less than zero.
        Returns

    3   The pow functions return xy .

### 7.12.7.5 [The sqrt functions]

    1 Synopsis
              #include <math.h>
               double sqrt(double x);
               float sqrtf(float x);
               long double sqrtl(long double x);
        Description

    2   The sqrt functions compute the nonnegative square root of x. A domain error occurs if
        the argument is less than zero.
        Returns

    3   The sqrt functions return √
                                  ⎯⎯x.

### 7.12.8 [Error and gamma functions]

### 7.12.8.1 [The erf functions]

    1 Synopsis
              #include <math.h>
               double erf(double x);
               float erff(float x);
               long double erfl(long double x);
        Description

    2   The erf functions compute the error function of x.
        Returns

    3                                      2   x

                                           ⎯⎯π ∫
                                                   −t 2
        The erf functions return erf x =         e dt.
                                           √   0

### 7.12.8.2 [The erfc functions]

    1 Synopsis
              #include <math.h>
               double erfc(double x);
               float erfcf(float x);
               long double erfcl(long double x);
        Description

    2   The erfc functions compute the complementary error function of x. A range error
        Returns

    3                                                     2   ∞
                                                         ⎯⎯π ∫
                                                                  −t 2
        The erfc functions return erfc x = 1 − erf x =         e dt.
                                                         √    x

### 7.12.8.3 [The lgamma functions]

    1 Synopsis
              #include <math.h>
               double lgamma(double x);
               float lgammaf(float x);
               long double lgammal(long double x);
        Description

    2   The lgamma functions compute the natural logarithm of the absolute value of gamma of
        x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
        or zero.
        Returns

    3   The lgamma functions return loge | Γ(x) |.

### 7.12.8.4 [The tgamma functions]

    1 Synopsis
              #include <math.h>
               double tgamma(double x);
               float tgammaf(float x);
               long double tgammal(long double x);
        Description

    2   The tgamma functions compute the gamma function of x. A domain error or pole error
        may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
        too large and may occur if the magnitude of x is too small.
        Returns

    3   The tgamma functions return Γ(x).

### 7.12.9 [Nearest integer functions]

### 7.12.9.1 [The ceil functions]

    1 Synopsis
              #include <math.h>
               double ceil(double x);
               float ceilf(float x);
               long double ceill(long double x);
        Description

    2   The ceil functions compute the smallest integer value not less than x.
        Returns

    3   The ceil functions return ⎡x⎤, expressed as a floating-point number.

### 7.12.9.2 [The floor functions]

    1 Synopsis
              #include <math.h>
               double floor(double x);
               float floorf(float x);
               long double floorl(long double x);
        Description

    2   The floor functions compute the largest integer value not greater than x.
        Returns

    3   The floor functions return ⎣x⎦, expressed as a floating-point number.

### 7.12.9.3 [The nearbyint functions]

    1 Synopsis
              #include <math.h>
               double nearbyint(double x);
               float nearbyintf(float x);
               long double nearbyintl(long double x);
        Description

    2   The nearbyint functions round their argument to an integer value in floating-point
        format, using the current rounding direction and without raising the ‘‘inexact’’ floating-
        point exception.
        Returns

    3   The nearbyint functions return the rounded integer value.

### 7.12.9.4 [The rint functions]

    1 Synopsis
              #include <math.h>
               double rint(double x);
               float rintf(float x);
               long double rintl(long double x);
        Description

    2   The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
        rint functions may raise the ‘‘inexact’’ floating-point exception if the result differs in
        value from the argument.
        Returns

    3   The rint functions return the rounded integer value.

### 7.12.9.5 [The lrint and llrint functions]

    1 Synopsis
              #include <math.h>
               long int lrint(double x);
               long int lrintf(float x);
               long int lrintl(long double x);
               long long int llrint(double x);
               long long int llrintf(float x);
               long long int llrintl(long double x);
        Description

    2   The lrint and llrint functions round their argument to the nearest integer value,
        rounding according to the current rounding direction. If the rounded value is outside the
        range of the return type, the numeric result is unspecified and a domain error or range
        error may occur.
        Returns

    3   The lrint and llrint functions return the rounded integer value.

### 7.12.9.6 [The round functions]

    1 Synopsis
              #include <math.h>
               double round(double x);
               float roundf(float x);
               long double roundl(long double x);
        Description

    2   The round functions round their argument to the nearest integer value in floating-point
        format, rounding halfway cases away from zero, regardless of the current rounding
        direction.
        Returns

    3   The round functions return the rounded integer value.

### 7.12.9.7 [The lround and llround functions]

    1 Synopsis
              #include <math.h>
               long int lround(double x);
               long int lroundf(float x);
               long int lroundl(long double x);
               long long int llround(double x);
               long long int llroundf(float x);
               long long int llroundl(long double x);
        Description

    2   The lround and llround functions round their argument to the nearest integer value,
        rounding halfway cases away from zero, regardless of the current rounding direction. If
        the rounded value is outside the range of the return type, the numeric result is unspecified
        and a domain error or range error may occur.
        Returns

    3   The lround and llround functions return the rounded integer value.

### 7.12.9.8 [The trunc functions]

    1 Synopsis
              #include <math.h>
               double trunc(double x);
               float truncf(float x);
               long double truncl(long double x);
        Description

    2   The trunc functions round their argument to the integer value, in floating format,
        nearest to but no larger in magnitude than the argument.
        Returns

    3   The trunc functions return the truncated integer value.

### 7.12.10 [Remainder functions]

### 7.12.10.1 [The fmod functions]

    1 Synopsis
                #include <math.h>
                 double fmod(double x, double y);
                 float fmodf(float x, float y);
                 long double fmodl(long double x, long double y);
        Description

    2   The fmod functions compute the floating-point remainder of x/y.
        Returns

    3   The fmod functions return the value x − ny, for some integer n such that, if y is nonzero,
        the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
        whether a domain error occurs or the fmod functions return zero is implementation-
        defined.

### 7.12.10.2 [The remainder functions]

    1 Synopsis
                #include <math.h>
                 double remainder(double x, double y);
                 float remainderf(float x, float y);
                 long double remainderl(long double x, long double y);
        Description

    2   The remainder functions compute the remainder x REM y required by IEC 60559.[239]
        Returns

    Footnote 239) ‘‘When y ≠ 0, the remainder r = x REM y is defined regardless of the rounding mode by the
             mathematical relation r = x − ny, where n is the integer nearest the exact value of x/y; whenever
             | n − x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.’’ This definition is applicable for
             all implementations.

    3   The remainder functions return x REM y. If y is zero, whether a domain error occurs
        or the functions return zero is implementation defined.

### 7.12.10.3 [The remquo functions]

    1 Synopsis
              #include <math.h>
               double remquo(double x, double y, int *quo);
               float remquof(float x, float y, int *quo);
               long double remquol(long double x, long double y,
                    int *quo);
        Description

    2   The remquo functions compute the same remainder as the remainder functions. In
        the object pointed to by quo they store a value whose sign is the sign of x/y and whose
        magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
        n is an implementation-defined integer greater than or equal to 3.
        Returns

    3   The remquo functions return x REM y. If y is zero, the value stored in the object
        pointed to by quo is unspecified and whether a domain error occurs or the functions
        return zero is implementation defined.

### 7.12.11 [Manipulation functions]

### 7.12.11.1 [The copysign functions]

    1 Synopsis
              #include <math.h>
               double copysign(double x, double y);
               float copysignf(float x, float y);
               long double copysignl(long double x, long double y);
        Description

    2   The copysign functions produce a value with the magnitude of x and the sign of y.
        They produce a NaN (with the sign of y) if x is a NaN. On implementations that
        represent a signed zero but do not treat negative zero consistently in arithmetic
        operations, the copysign functions regard the sign of zero as positive.
        Returns

    3   The copysign functions return a value with the magnitude of x and the sign of y.

### 7.12.11.2 [The nan functions]

    1 Synopsis
               #include <math.h>
                double nan(const char *tagp);
                float nanf(const char *tagp);
                long double nanl(const char *tagp);
        Description

    2   The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
        sequence)",     (char**)       NULL); the call nan("") is equivalent to
        strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
        sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
        NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
        and strtold.
        Returns

    3   The nan functions return a quiet NaN, if available, with content indicated through tagp.
        If the implementation does not support quiet NaNs, the functions return zero.
        Forward references: the strtod, strtof, and strtold functions (7.22.1.3).

### 7.12.11.3 [The nextafter functions]

    1 Synopsis
               #include <math.h>
                double nextafter(double x, double y);
                float nextafterf(float x, float y);
                long double nextafterl(long double x, long double y);
        Description

    2   The nextafter functions determine the next representable value, in the type of the
        function, after x in the direction of y, where x and y are first converted to the type of the
        function.[240] The nextafter functions return y if x equals y. A range error may occur
        if the magnitude of x is the largest finite value representable in the type and the result is
        infinite or not representable in the type.
        Returns

    Footnote 240) The argument values are converted to the type of the function, even by a macro implementation of the
             function.

    3   The nextafter functions return the next representable value in the specified format
        after x in the direction of y.

### 7.12.11.4 [The nexttoward functions]

    1 Synopsis
               #include <math.h>
                double nexttoward(double x, long double y);
                float nexttowardf(float x, long double y);
                long double nexttowardl(long double x, long double y);
        Description

    2   The nexttoward functions are equivalent to the nextafter functions except that the
        second parameter has type long double and the functions return y converted to the
        type of the function if x equals y.[241]

    Footnote 241) The result of the nexttoward functions is determined in the type of the function, without loss of
             range or precision in a floating second argument.

### 7.12.12 [Maximum, minimum, and positive difference functions]

### 7.12.12.1 [The fdim functions]

    1 Synopsis
               #include <math.h>
                double fdim(double x, double y);
                float fdimf(float x, float y);
                long double fdiml(long double x, long double y);
        Description

    2   The fdim functions determine the positive difference between their arguments:
              ⎧x − y if x > y
              ⎨
              ⎩+0     if x ≤ y
        A range error may occur.
        Returns

    3   The fdim functions return the positive difference value.

### 7.12.12.2 [The fmax functions]

    1 Synopsis
               #include <math.h>
                double fmax(double x, double y);
                float fmaxf(float x, float y);
                long double fmaxl(long double x, long double y);
        Description

    2   The fmax functions determine the maximum numeric value of their arguments.[242]
        Returns

    Footnote 242) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the
             fmax functions choose the numeric value. See F.10.9.2.

    3   The fmax functions return the maximum numeric value of their arguments.

### 7.12.12.3 [The fmin functions]

    1 Synopsis
               #include <math.h>
                double fmin(double x, double y);
                float fminf(float x, float y);
                long double fminl(long double x, long double y);
        Description

    2   The fmin functions determine the minimum numeric value of their arguments.[243]
        Returns

    Footnote 243) The fmin functions are analogous to the fmax functions in their treatment of NaNs.

    3   The fmin functions return the minimum numeric value of their arguments.

### 7.12.13 [Floating multiply-add]

### 7.12.13.1 [The fma functions]

    1 Synopsis
               #include <math.h>
                double fma(double x, double y, double z);
                float fmaf(float x, float y, float z);
                long double fmal(long double x, long double y,
                     long double z);
        Description

    2   The fma functions compute (x × y) + z, rounded as one ternary operation: they compute
        the value (as if) to infinite precision and round once to the result format, according to the
        current rounding mode. A range error may occur.
        Returns

    3   The fma functions return (x × y) + z, rounded as one ternary operation.

### 7.12.14 [Comparison macros]

    1   The relational and equality operators support the usual mathematical relationships
        between numeric values. For any ordered pair of numeric values exactly one of the
        relationships — less, greater, and equal — is true. Relational operators may raise the
        ‘‘invalid’’ floating-point exception when argument values are NaNs. For a NaN and a
        numeric value, or for two NaNs, just the unordered relationship is true.[244] The following
        subclauses provide macros that are quiet (non floating-point exception raising) versions
        of the relational operators, and other comparison macros that facilitate writing efficient
        code that accounts for NaNs without suffering the ‘‘invalid’’ floating-point exception. In
        the synopses in this subclause, real-floating indicates that the argument shall be an
        expression of real floating type[245] (both arguments need not have the same type).[246]

    Footnote 244) IEC 60559 requires that the built-in relational operators raise the ‘‘invalid’’ floating-point exception if
             the operands compare unordered, as an error indicator for programs written without consideration of
             NaNs; the result in these cases is false.

    Footnote 245) If any argument is of integer type, or any other type that is not a real floating type, the behavior is
             undefined.

    Footnote 246) Whether an argument represented in a format wider than its semantic type is converted to the semantic
             type is unspecified.

### 7.12.14.1 [The isgreater macro]

    1 Synopsis
                #include <math.h>
                 int isgreater(real-floating x, real-floating y);
        Description

    2   The isgreater macro determines whether its first argument is greater than its second
        argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
        unlike (x) > (y), isgreater(x, y) does not raise the ‘‘invalid’’ floating-point
        exception when x and y are unordered.
        Returns

    3   The isgreater macro returns the value of (x) > (y).

### 7.12.14.2 [The isgreaterequal macro]

    1 Synopsis
                #include <math.h>
                 int isgreaterequal(real-floating x, real-floating y);
        Description

    2   The isgreaterequal macro determines whether its first argument is greater than or
        equal to its second argument. The value of isgreaterequal(x, y) is always equal
        to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
        not raise the ‘‘invalid’’ floating-point exception when x and y are unordered.
        Returns

    3   The isgreaterequal macro returns the value of (x) >= (y).

### 7.12.14.3 [The isless macro]

    1 Synopsis
             #include <math.h>
              int isless(real-floating x, real-floating y);
        Description

    2   The isless macro determines whether its first argument is less than its second
        argument. The value of isless(x, y) is always equal to (x) < (y); however,
        unlike (x) < (y), isless(x, y) does not raise the ‘‘invalid’’ floating-point
        exception when x and y are unordered.
        Returns

    3   The isless macro returns the value of (x) < (y).

### 7.12.14.4 [The islessequal macro]

    1 Synopsis
             #include <math.h>
              int islessequal(real-floating x, real-floating y);
        Description

    2   The islessequal macro determines whether its first argument is less than or equal to
        its second argument. The value of islessequal(x, y) is always equal to
        (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
        the ‘‘invalid’’ floating-point exception when x and y are unordered.
        Returns

    3   The islessequal macro returns the value of (x) <= (y).

### 7.12.14.5 [The islessgreater macro]

    1 Synopsis
              #include <math.h>
               int islessgreater(real-floating x, real-floating y);
        Description

    2   The islessgreater macro determines whether its first argument is less than or
        greater than its second argument. The islessgreater(x, y) macro is similar to
        (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
        the ‘‘invalid’’ floating-point exception when x and y are unordered (nor does it evaluate x
        and y twice).
        Returns

    3   The islessgreater macro returns the value of (x) < (y) || (x) > (y).

### 7.12.14.6 [The isunordered macro]

    1 Synopsis
              #include <math.h>
               int isunordered(real-floating x, real-floating y);
        Description

    2   The isunordered macro determines whether its arguments are unordered.
        Returns

    3   The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.

### 7.13 [Nonlocal jumps <setjmp.h>]

    1   The header <setjmp.h> defines the macro setjmp, and declares one function and
        one type, for bypassing the normal function call and return discipline.[247]

    Footnote 247) These functions are useful for dealing with unusual conditions encountered in a low-level function of
             a program.

    2   The type declared is
                jmp_buf
        which is an array type suitable for holding the information needed to restore a calling
        environment. The environment of a call to the setjmp macro consists of information
        sufficient for a call to the longjmp function to return execution to the correct block and
        invocation of that block, were it called recursively. It does not include the state of the
        floating-point status flags, of open files, or of any other component of the abstract
        machine.

    3   It is unspecified whether setjmp is a macro or an identifier declared with external
        linkage. If a macro definition is suppressed in order to access an actual function, or a
        program defines an external identifier with the name setjmp, the behavior is undefined.

### 7.13.1 [Save calling environment]

### 7.13.1.1 [The setjmp macro]

    1 Synopsis
               #include <setjmp.h>
                int setjmp(jmp_buf env);
        Description

    2   The setjmp macro saves its calling environment in its jmp_buf argument for later use
        by the longjmp function.
        Returns

    3   If the return is from a direct invocation, the setjmp macro returns the value zero. If the
        return is from a call to the longjmp function, the setjmp macro returns a nonzero
        value.
        Environmental limits

    4   An invocation of the setjmp macro shall appear only in one of the following contexts:
        — the entire controlling expression of a selection or iteration statement;
        — one operand of a relational or equality operator with the other operand an integer
          constant expression, with the resulting expression being the entire controlling
            expression of a selection or iteration statement;
        — the operand of a unary ! operator with the resulting expression being the entire
          controlling expression of a selection or iteration statement; or
        — the entire expression of an expression statement (possibly cast to void).

    5   If the invocation appears in any other context, the behavior is undefined.

### 7.13.2 [Restore calling environment]

### 7.13.2.1 [The longjmp function]

    1 Synopsis
                #include <setjmp.h>
                 _Noreturn void longjmp(jmp_buf env, int val);
        Description

    2   The longjmp function restores the environment saved by the most recent invocation of
        the setjmp macro in the same invocation of the program with the corresponding
        jmp_buf argument. If there has been no such invocation, or if the invocation was from
        another thread of execution, or if the function containing the invocation of the setjmp
        macro has terminated execution[248] in the interim, or if the invocation of the setjmp
        macro was within the scope of an identifier with variably modified type and execution has
        left that scope in the interim, the behavior is undefined.

    Footnote 248) For example, by executing a return statement or because another longjmp call has caused a
             transfer to a setjmp invocation in a function earlier in the set of nested calls.

    3   All accessible objects have values, and all other components of the abstract machine[249]
        have state, as of the time the longjmp function was called, except that the values of
        objects of automatic storage duration that are local to the function containing the
        invocation of the corresponding setjmp macro that do not have volatile-qualified type
        and have been changed between the setjmp invocation and longjmp call are
        indeterminate.
        Returns

    Footnote 249) This includes, but is not limited to, the floating-point status flags and the state of open files.

    4   After longjmp is completed, thread execution continues as if the corresponding
        invocation of the setjmp macro had just returned the value specified by val. The
        longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
        the setjmp macro returns the value 1.

    5   EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
        might cause memory associated with a variable length array object to be squandered.
    #include <setjmp.h>
    jmp_buf buf;
    void g(int n);
    void h(int n);
    int n = 6;
    void f(void)
    {
          int x[n];          // valid: f is not terminated
          setjmp(buf);
          g(n);
    }
    void g(int n)
    {
          int a[n];          // a may remain allocated
          h(n);
    }
    void h(int n)
    {
          int b[n];          // b may remain allocated
          longjmp(buf, 2);   // might cause memory loss
    }

### 7.14 [Signal handling <signal.h>]

    1   The header <signal.h> declares a type and two functions and defines several macros,
        for handling various signals (conditions that may be reported during program execution).

    2   The type defined is
                 sig_atomic_t
        which is the (possibly volatile-qualified) integer type of an object that can be accessed as
        an atomic entity, even in the presence of asynchronous interrupts.

    3   The macros defined are
                 SIG_DFL
                 SIG_ERR
                 SIG_IGN
        which expand to constant expressions with distinct values that have type compatible with
        the second argument to, and the return value of, the signal function, and whose values
        compare unequal to the address of any declarable function; and the following, which
        expand to positive integer constant expressions with type int and distinct values that are
        the signal numbers, each corresponding to the specified condition:
                 SIGABRT abnormal termination, such as is initiated by the abort function
                 SIGFPE        an erroneous arithmetic operation, such as zero divide or an operation
                               resulting in overflow
                 SIGILL        detection of an invalid function image, such as an invalid instruction
                 SIGINT        receipt of an interactive attention signal
                 SIGSEGV an invalid access to storage
                 SIGTERM a termination request sent to the program

    4   An implementation need not generate any of these signals, except as a result of explicit
        calls to the raise function. Additional signals and pointers to undeclarable functions,
        with macro definitions beginning, respectively, with the letters SIG and an uppercase
        letter or with SIG_ and an uppercase letter,[250] may also be specified by the
        implementation. The complete set of signals, their semantics, and their default handling
        is implementation-defined; all signal numbers shall be positive.

    Footnote 250) See ‘‘future library directions’’ (7.31.7). The names of the signal numbers reflect the following terms
             (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
             and termination.

### 7.14.1 [Specify signal handling]

### 7.14.1.1 [The signal function]

    1 Synopsis
                #include <signal.h>
                 void (*signal(int sig, void (*func)(int)))(int);
        Description

    2   The signal function chooses one of three ways in which receipt of the signal number
        sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
        for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
        Otherwise, func shall point to a function to be called when that signal occurs. An
        invocation of such a function because of a signal, or (recursively) of any further functions
        called by that invocation (other than functions in the standard library),[251] is called a
        signal handler.

    Footnote 251) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler
             called via the abort function).

    3   When a signal occurs and func points to a function, it is implementation-defined
        whether the equivalent of signal(sig, SIG_DFL); is executed or the
        implementation prevents some implementation-defined set of signals (at least including
        sig) from occurring until the current signal handling has completed; in the case of
        SIGILL, the implementation may alternatively define that no action is taken. Then the
        equivalent of (*func)(sig); is executed. If and when the function returns, if the
        value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
        value corresponding to a computational exception, the behavior is undefined; otherwise
        the program will resume execution at the point it was interrupted.

    4   If the signal occurs as the result of calling the abort or raise function, the signal
        handler shall not call the raise function.

    5   If the signal occurs other than as the result of calling the abort or raise function, the
        behavior is undefined if the signal handler refers to any object with static or thread
        storage duration that is not a lock-free atomic object other than by assigning a value to an
        object declared as volatile sig_atomic_t, or the signal handler calls any function
        in the standard library other than the abort function, the _Exit function, the
        quick_exit function, or the signal function with the first argument equal to the
        signal number corresponding to the signal that caused the invocation of the handler.
        Furthermore, if such a call to the signal function results in a SIG_ERR return, the
        value of errno is indeterminate.[252]

    Footnote 252) If any signal is generated by an asynchronous signal handler, the behavior is undefined.

    6   At program startup, the equivalent of
               signal(sig, SIG_IGN);
        may be executed for some signals selected in an implementation-defined manner; the
        equivalent of
               signal(sig, SIG_DFL);
        is executed for all other signals defined by the implementation.

    7   Use of this function in a multi-threaded program results in undefined behavior. The
        implementation shall behave as if no library function calls the signal function.
        Returns

    8   If the request can be honored, the signal function returns the value of func for the
        most recent successful call to signal for the specified signal sig. Otherwise, a value of
        SIG_ERR is returned and a positive value is stored in errno.
        Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
        _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).

### 7.14.2 [Send signal]

### 7.14.2.1 [The raise function]

    1 Synopsis
              #include <signal.h>
               int raise(int sig);
        Description

    2   The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
        signal handler is called, the raise function shall not return until after the signal handler
        does.
        Returns

    3   The raise function returns zero if successful, nonzero if unsuccessful.

### 7.15 [Alignment <stdalign.h>]

    1   The header <stdalign.h> defines four macros.

    2   The macro
               alignas
        expands to _Alignas; the macro
               alignof
        expands to _Alignof.

    3   The remaining macros are suitable for use in #if preprocessing directives. They are
               _ _alignas_is_defined
        and
               _ _alignof_is_defined
        which both expand to the integer constant 1.

### 7.16 [Variable arguments <stdarg.h>]

    1   The header <stdarg.h> declares a type and defines four macros, for advancing
        through a list of arguments whose number and types are not known to the called function
        when it is translated.

    2   A function may be called with a variable number of arguments of varying types. As
        described in 6.9.1, its parameter list contains one or more parameters. The rightmost
        parameter plays a special role in the access mechanism, and will be designated parmN in
        this description.

    3   The type declared is
                va_list
        which is a complete object type suitable for holding information needed by the macros
        va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
        desired, the called function shall declare an object (generally referred to as ap in this
        subclause) having type va_list. The object ap may be passed as an argument to
        another function; if that function invokes the va_arg macro with parameter ap, the
        value of ap in the calling function is indeterminate and shall be passed to the va_end
        macro prior to any further reference to ap.[253]

    Footnote 253) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
             case the original function may make further use of the original list after the other function returns.

### 7.16.1 [Variable argument list access macros]

    1   The va_start and va_arg macros described in this subclause shall be implemented
        as macros, not functions. It is unspecified whether va_copy and va_end are macros or
        identifiers declared with external linkage. If a macro definition is suppressed in order to
        access an actual function, or a program defines an external identifier with the same name,
        the behavior is undefined. Each invocation of the va_start and va_copy macros
        shall be matched by a corresponding invocation of the va_end macro in the same
        function.

### 7.16.1.1 [The va_arg macro]

    1 Synopsis
               #include <stdarg.h>
                type va_arg(va_list ap, type);
        Description

    2   The va_arg macro expands to an expression that has the specified type and the value of
        the next argument in the call. The parameter ap shall have been initialized by the
        va_start or va_copy macro (without an intervening invocation of the va_end
        macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
        values of successive arguments are returned in turn. The parameter type shall be a type
        name specified such that the type of a pointer to an object that has the specified type can
        be obtained simply by postfixing a * to type. If there is no actual next argument, or if
        type is not compatible with the type of the actual next argument (as promoted according
        to the default argument promotions), the behavior is undefined, except for the following
        cases:
        — one type is a signed integer type, the other type is the corresponding unsigned integer
          type, and the value is representable in both types;
        — one type is pointer to void and the other is a pointer to a character type.
        Returns

    3   The first invocation of the va_arg macro after that of the va_start macro returns the
        value of the argument after that specified by parmN . Successive invocations return the
        values of the remaining arguments in succession.

### 7.16.1.2 [The va_copy macro]

    1 Synopsis
              #include <stdarg.h>
               void va_copy(va_list dest, va_list src);
        Description

    2   The va_copy macro initializes dest as a copy of src, as if the va_start macro had
        been applied to dest followed by the same sequence of uses of the va_arg macro as
        had previously been used to reach the present state of src. Neither the va_copy nor
        va_start macro shall be invoked to reinitialize dest without an intervening
        invocation of the va_end macro for the same dest.
        Returns

    3   The va_copy macro returns no value.

### 7.16.1.3 [The va_end macro]

    1 Synopsis
              #include <stdarg.h>
               void va_end(va_list ap);
        Description

    2   The va_end macro facilitates a normal return from the function whose variable
        argument list was referred to by the expansion of the va_start macro, or the function
        containing the expansion of the va_copy macro, that initialized the va_list ap. The
        va_end macro may modify ap so that it is no longer usable (without being reinitialized
        by the va_start or va_copy macro). If there is no corresponding invocation of the
        va_start or va_copy macro, or if the va_end macro is not invoked before the
        return, the behavior is undefined.
        Returns

    3   The va_end macro returns no value.

### 7.16.1.4 [The va_start macro]

    1 Synopsis
               #include <stdarg.h>
                void va_start(va_list ap, parmN);
        Description

    2   The va_start macro shall be invoked before any access to the unnamed arguments.

    3   The va_start macro initializes ap for subsequent use by the va_arg and va_end
        macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
        without an intervening invocation of the va_end macro for the same ap.

    4   The parameter parmN is the identifier of the rightmost parameter in the variable
        parameter list in the function definition (the one just before the , ...). If the parameter
        parmN is declared with the register storage class, with a function or array type, or
        with a type that is not compatible with the type that results after application of the default
        argument promotions, the behavior is undefined.
        Returns

    5   The va_start macro returns no value.

    6   EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
        more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
        pointers is specified by the first argument to f1.
                #include <stdarg.h>
                #define MAXARGS   31
                void f1(int n_ptrs, ...)
                {
                      va_list ap;
                      char *array[MAXARGS];
                      int ptr_no = 0;
                          if (n_ptrs > MAXARGS)
                                n_ptrs = MAXARGS;
                          va_start(ap, n_ptrs);
                          while (ptr_no < n_ptrs)
                                array[ptr_no++] = va_arg(ap, char *);
                          va_end(ap);
                          f2(n_ptrs, array);
                 }
        Each call to f1 is required to have visible the definition of the function or a declaration such as
                 void f1(int, ...);

    7   EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
        indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
        is gathered again and passed to function f4.
                 #include <stdarg.h>
                 #define MAXARGS 31
                 void f3(int n_ptrs, int f4_after, ...)
                 {
                       va_list ap, ap_save;
                       char *array[MAXARGS];
                       int ptr_no = 0;
                       if (n_ptrs > MAXARGS)
                             n_ptrs = MAXARGS;
                       va_start(ap, f4_after);
                       while (ptr_no < n_ptrs) {
                             array[ptr_no++] = va_arg(ap, char *);
                             if (ptr_no == f4_after)
                                   va_copy(ap_save, ap);
                       }
                       va_end(ap);
                       f2(n_ptrs, array);
                          // Now process the saved copy.
                          n_ptrs -= f4_after;
                          ptr_no = 0;
                          while (ptr_no < n_ptrs)
                                array[ptr_no++] = va_arg(ap_save, char *);
                          va_end(ap_save);
                          f4(n_ptrs, array);
                 }

### 7.17 [Atomics <stdatomic.h>]

### 7.17.1 [Introduction]

    1   The header <stdatomic.h> defines several macros and declares several types and
        functions for performing atomic operations on data shared between threads.[254]

    Footnote 254) See ‘‘future library directions’’ (7.31.8).

    2   Implementations that define the macro _ _STDC_NO_ATOMICS_ _ need not provide
        this header nor support any of its facilities.

    3   The macros defined are the atomic lock-free macros
                 ATOMIC_BOOL_LOCK_FREE
                 ATOMIC_CHAR_LOCK_FREE
                 ATOMIC_CHAR16_T_LOCK_FREE
                 ATOMIC_CHAR32_T_LOCK_FREE
                 ATOMIC_WCHAR_T_LOCK_FREE
                 ATOMIC_SHORT_LOCK_FREE
                 ATOMIC_INT_LOCK_FREE
                 ATOMIC_LONG_LOCK_FREE
                 ATOMIC_LLONG_LOCK_FREE
                 ATOMIC_POINTER_LOCK_FREE
        which indicate the lock-free property of the corresponding atomic types (both signed and
        unsigned); and
                 ATOMIC_FLAG_INIT
        which expands to an initializer for an object of type atomic_flag.

    4   The types include
                 memory_order
        which is an enumerated type whose enumerators identify memory ordering constraints;
                 atomic_flag
        which is a structure type representing a lock-free, primitive atomic flag; and several ∗
        atomic analogs of integer types.

    5   In the following synopses:
        — An A refers to one of the atomic types.
        — A C refers to its corresponding non-atomic type.                                         ∗
        — An M refers to the type of the other argument for arithmetic operations. For atomic
          integer types, M is C. For atomic pointer types, M is ptrdiff_t.
        — The functions not ending in _explicit have the same semantics as the
          corresponding _explicit function with memory_order_seq_cst for the
          memory_order argument.

    6   NOTE Many operations are volatile-qualified. The ‘‘volatile as device register’’ semantics have not
        changed in the standard. This qualification means that volatility is preserved when applying these
        operations to volatile objects.

### 7.17.2 [Initialization]

### 7.17.2.1 [The ATOMIC_VAR_INIT macro]

    1 Synopsis
               #include <stdatomic.h>
                #define ATOMIC_VAR_INIT(C value)
        Description

    2   The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
        atomic object of a type that is initialization-compatible with value. An atomic object
        with automatic storage duration that is not explicitly initialized using
        ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
        initialization for objects with static or thread-local storage duration is guaranteed to
        produce a valid state.

    3   Concurrent access to the variable being initialized, even via an atomic operation,
        constitutes a data race.

    4   EXAMPLE
                atomic_int guide = ATOMIC_VAR_INIT(42);

### 7.17.2.2 [The atomic_init generic function]

    1 Synopsis
               #include <stdatomic.h>
                void atomic_init(volatile A *obj, C value);
        Description

    2   The atomic_init generic function initializes the atomic object pointed to by obj to
        the value value, while also initializing any additional state that the implementation
        might need to carry for the atomic object.

    3   Although this function initializes an atomic object, it does not avoid data races;
        concurrent access to the variable being initialized, even via an atomic operation,
        constitutes a data race.
        Returns

    4   The atomic_init generic function returns no value.

    5   EXAMPLE
                 atomic_int guide;
                 atomic_init(&guide, 42);

### 7.17.3 [Order and consistency]

    1   The enumerated type memory_order specifies the detailed regular (non-atomic)
        memory synchronization operations as defined in 5.1.2.4 and may provide for operation
        ordering. Its enumeration constants are as follows:[255]
                 memory_order_relaxed
                 memory_order_consume
                 memory_order_acquire
                 memory_order_release
                 memory_order_acq_rel
                 memory_order_seq_cst

    Footnote 255) See ‘‘future library directions’’ (7.31.8).

    2   For memory_order_relaxed, no operation orders memory.

    3   For       memory_order_release,       memory_order_acq_rel,             and
        memory_order_seq_cst, a store operation performs a release operation on the
        affected memory location.

    4   For       memory_order_acquire,       memory_order_acq_rel,             and
        memory_order_seq_cst, a load operation performs an acquire operation on the
        affected memory location.

    5   For memory_order_consume, a load operation performs a consume operation on the
        affected memory location.

    6   There shall be a single total order S on all memory_order_seq_cst operations,
        consistent with the ‘‘happens before’’ order and modification orders for all affected
        locations, such that each memory_order_seq_cst operation B that loads a value
        from an atomic object M observes one of the following values:
        — the result of the last modification A of M that precedes B in S, if it exists, or
        — if A exists, the result of some modification of M in the visible sequence of side
          effects with respect to B that is not memory_order_seq_cst and that does not
          happen before A, or
         — if A does not exist, the result of some modification of M in the visible sequence of
            side effects with respect to B that is not memory_order_seq_cst.

    7    NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
         an order that does include lock and unlock operations, since the ordering between those is already included
         in the ‘‘happens before’’ ordering.

    8    NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
         memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic
         object be indivisible with respect to all other atomic accesses to that object.

    9    For an atomic operation B that reads the value of an atomic object M, if there is a
         memory_order_seq_cst fence X sequenced before B, then B observes either the
         last memory_order_seq_cst modification of M preceding X in the total order S or
         a later modification of M in its modification order.

    10   For atomic operations A and B on an atomic object M, where A modifies M and B takes
         its value, if there is a memory_order_seq_cst fence X such that A is sequenced
         before X and B follows X in S, then B observes either the effects of A or a later
         modification of M in its modification order.

    11   For atomic operations A and B on an atomic object M, where A modifies M and B takes
         its value, if there are memory_order_seq_cst fences X and Y such that A is
         sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes
         either the effects of A or a later modification of M in its modification order.

    12   Atomic read-modify-write operations shall always read the last value (in the modification
         order) stored before the write associated with the read-modify-write operation.

    13   An atomic store shall only store a value that has been computed from constants and
         program input values by a finite sequence of program evaluations, such that each
         evaluation observes the values of variables as computed by the last prior assignment in
         the sequence.[256] The ordering of evaluations in this sequence shall be such that
         — If an evaluation B observes a value computed by A in a different thread, then B does
           not happen before A.
         — If an evaluation A is included in the sequence, then all evaluations that assign to the
           same variable and happen before A are also included.

    Footnote 256) Among other implications, atomic variables shall not decay.

    14   NOTE 3 The second requirement disallows ‘‘out-of-thin-air’’, or ‘‘speculative’’ stores of atomics when
         relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
         sequence out of thread order. For example, with x and y initially zero,
                 // Thread 1:
                 r1 = atomic_load_explicit(&y, memory_order_relaxed);
                 atomic_store_explicit(&x, r1, memory_order_relaxed);

                 // Thread 2:
                 r2 = atomic_load_explicit(&x, memory_order_relaxed);
                 atomic_store_explicit(&y, 42, memory_order_relaxed);
         is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:
                 atomic_store_explicit(&y, 42, memory_order_relaxed);
                 r1 = atomic_load_explicit(&y, memory_order_relaxed);
                 atomic_store_explicit(&x, r1, memory_order_relaxed);
                 r2 = atomic_load_explicit(&x, memory_order_relaxed);
         On the other hand,
                 // Thread 1:
                 r1 = atomic_load_explicit(&y, memory_order_relaxed);
                 atomic_store_explicit(&x, r1, memory_order_relaxed);

                 // Thread 2:
                 r2 = atomic_load_explicit(&x, memory_order_relaxed);
                 atomic_store_explicit(&y, r2, memory_order_relaxed);
         is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results
         in the computation of 42. In the absence of ‘‘relaxed’’ operations and read-modify-write operations with
         weaker than memory_order_acq_rel ordering, the second requirement has no impact.

         Recommended practice

    15   The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
         with x and y initially zero:
                 // Thread 1:
                 r1 = atomic_load_explicit(&x, memory_order_relaxed);
                 if (r1 == 42)
                      atomic_store_explicit(&y, r1, memory_order_relaxed);

                 // Thread 2:
                 r2 = atomic_load_explicit(&y, memory_order_relaxed);
                 if (r2 == 42)
                      atomic_store_explicit(&x, 42, memory_order_relaxed);
         However, this is not useful behavior, and implementations should not allow it.

    16   Implementations should make atomic stores visible to atomic loads within a reasonable
         amount of time.

### 7.17.3.1 [The kill_dependency macro]

    1 Synopsis
              #include <stdatomic.h>
               type kill_dependency(type y);
        Description

    2   The kill_dependency macro terminates a dependency chain; the argument does not
        carry a dependency to the return value.
        Returns

    3   The kill_dependency macro returns the value of y.

### 7.17.4 [Fences]

    1   This subclause introduces synchronization primitives called fences. Fences can have
        acquire semantics, release semantics, or both. A fence with acquire semantics is called
        an acquire fence; a fence with release semantics is called a release fence.

    2   A release fence A synchronizes with an acquire fence B if there exist atomic operations
        X and Y , both operating on some atomic object M, such that A is sequenced before X, X
        modifies M, Y is sequenced before B, and Y reads the value written by X or a value
        written by any side effect in the hypothetical release sequence X would head if it were a
        release operation.

    3   A release fence A synchronizes with an atomic operation B that performs an acquire
        operation on an atomic object M if there exists an atomic operation X such that A is
        sequenced before X, X modifies M, and B reads the value written by X or a value written
        by any side effect in the hypothetical release sequence X would head if it were a release
        operation.

    4   An atomic operation A that is a release operation on an atomic object M synchronizes
        with an acquire fence B if there exists some atomic operation X on M such that X is
        sequenced before B and reads the value written by A or a value written by any side effect
        in the release sequence headed by A.

### 7.17.4.1 [The atomic_thread_fence function]

    1 Synopsis
              #include <stdatomic.h>
               void atomic_thread_fence(memory_order order);
        Description

    2   Depending on the value of order, this operation:
        — has no effects, if order == memory_order_relaxed;
        — is an acquire fence, if order == memory_order_acquire or order ==
          memory_order_consume;
        — is a release fence, if order == memory_order_release;
        — is both an acquire fence                    and     a    release    fence,     if   order        ==
          memory_order_acq_rel;
        — is a sequentially consistent acquire and release fence, if order                                 ==
          memory_order_seq_cst.
        Returns

    3   The atomic_thread_fence function returns no value.

### 7.17.4.2 [The atomic_signal_fence function]

    1 Synopsis
               #include <stdatomic.h>
                void atomic_signal_fence(memory_order order);
        Description

    2   Equivalent to atomic_thread_fence(order), except that the resulting ordering
        constraints are established only between a thread and a signal handler executed in the
        same thread.

    3   NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
        performed by the thread become visible to the signal handler.

    4   NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
        atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
        have inserted are not emitted.

        Returns

    5   The atomic_signal_fence function returns no value.

### 7.17.5 [Lock-free property]

    1   The atomic lock-free macros indicate the lock-free property of integer and address atomic
        types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
        the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.

    2   NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
        memory location via two different addresses will communicate atomically. The implementation should not
        depend on any per-process state. This restriction enables communication via memory mapped into a
        process more than once and memory shared between two processes.

### 7.17.5.1 [The atomic_is_lock_free generic function]

    1 Synopsis
                #include <stdatomic.h>
                 _Bool atomic_is_lock_free(const volatile A *obj);
        Description

    2   The atomic_is_lock_free generic function indicates whether or not the object
        pointed to by obj is lock-free.                                              ∗
        Returns

    3   The atomic_is_lock_free generic function returns nonzero (true) if and only if the
        object’s operations are lock-free. The result of a lock-free query on one object cannot be
        inferred from the result of a lock-free query on another object.

### 7.17.6 [Atomic integer types]

    1   For each line in the following table,[257] the atomic type name is declared as a type that
        has the same representation and alignment requirements as the corresponding direct
        type.[258]
                   Atomic type name                           Direct type
               atomic_bool                           _Atomic _Bool
               atomic_char                           _Atomic char
               atomic_schar                          _Atomic signed char
               atomic_uchar                          _Atomic unsigned char
               atomic_short                          _Atomic short
               atomic_ushort                         _Atomic unsigned short
               atomic_int                            _Atomic int
               atomic_uint                           _Atomic unsigned int
               atomic_long                           _Atomic long
               atomic_ulong                          _Atomic unsigned long
               atomic_llong                          _Atomic long long
               atomic_ullong                         _Atomic unsigned long long
               atomic_char16_t                       _Atomic char16_t
               atomic_char32_t                       _Atomic char32_t
               atomic_wchar_t                        _Atomic wchar_t
               atomic_int_least8_t                   _Atomic int_least8_t
               atomic_uint_least8_t                  _Atomic uint_least8_t
               atomic_int_least16_t                  _Atomic int_least16_t
               atomic_uint_least16_t                 _Atomic uint_least16_t
               atomic_int_least32_t                  _Atomic int_least32_t
               atomic_uint_least32_t                 _Atomic uint_least32_t
               atomic_int_least64_t                  _Atomic int_least64_t
               atomic_uint_least64_t                 _Atomic uint_least64_t
               atomic_int_fast8_t                    _Atomic int_fast8_t
               atomic_uint_fast8_t                   _Atomic uint_fast8_t
               atomic_int_fast16_t                   _Atomic int_fast16_t
               atomic_uint_fast16_t                  _Atomic uint_fast16_t
               atomic_int_fast32_t                   _Atomic int_fast32_t
               atomic_uint_fast32_t                  _Atomic uint_fast32_t
               atomic_int_fast64_t                   _Atomic int_fast64_t
               atomic_uint_fast64_t                  _Atomic uint_fast64_t
               atomic_intptr_t                       _Atomic intptr_t
               atomic_uintptr_t                      _Atomic uintptr_t
               atomic_size_t                         _Atomic size_t
               atomic_ptrdiff_t                      _Atomic ptrdiff_t
               atomic_intmax_t                       _Atomic intmax_t
               atomic_uintmax_t                      _Atomic uintmax_t

    Footnote 257) See ‘‘future library directions’’ (7.31.8).

    Footnote 258) The same representation and alignment requirements are meant to imply interchangeability as
             arguments to functions, return values from functions, and members of unions.

    2   The semantics of the operations on these types are defined in 7.17.7.     ∗

    3   NOTE The representation of atomic integer types need not have the same size as their corresponding
        regular types. They should have the same size whenever possible, as it eases effort required to port existing
        code.

### 7.17.7 [Operations on atomic types]

    1   There are only a few kinds of operations on atomic types, though there are many
        instances of those kinds. This subclause specifies each general kind.

### 7.17.7.1 [The atomic_store generic functions]

    1 Synopsis
                #include <stdatomic.h>
                 void atomic_store(volatile A *object, C desired);
                 void atomic_store_explicit(volatile A *object,
                      C desired, memory_order order);
        Description

    2   The      order      argument    shall    not    be    memory_order_acquire,
        memory_order_consume, nor memory_order_acq_rel. Atomically replace the
        value pointed to by object with the value of desired. Memory is affected according
        to the value of order.
        Returns

    3   The atomic_store generic functions return no value.

### 7.17.7.2 [The atomic_load generic functions]

    1 Synopsis
                #include <stdatomic.h>
                 C atomic_load(volatile A *object);
                 C atomic_load_explicit(volatile A *object,
                      memory_order order);
        Description

    2   The order argument shall not be memory_order_release nor
        memory_order_acq_rel. Memory is affected according to the value of order.
        Returns
        Atomically returns the value pointed to by object.

### 7.17.7.3 [The atomic_exchange generic functions]

    1 Synopsis
                #include <stdatomic.h>
                 C atomic_exchange(volatile A *object, C desired);
                 C atomic_exchange_explicit(volatile A *object,
                      C desired, memory_order order);
        Description

    2   Atomically replace the value pointed to by object with desired. Memory is affected
        according to the value of order. These operations are read-modify-write operations
        (5.1.2.4).
        Returns

    3   Atomically returns the value pointed to by object immediately before the effects.

### 7.17.7.4 [The atomic_compare_exchange generic functions]

    1 Synopsis
                #include <stdatomic.h>
                 _Bool atomic_compare_exchange_strong(volatile A *object,
                      C *expected, C desired);
                 _Bool atomic_compare_exchange_strong_explicit(
                      volatile A *object, C *expected, C desired,
                      memory_order success, memory_order failure);
                 _Bool atomic_compare_exchange_weak(volatile A *object,
                      C *expected, C desired);
                 _Bool atomic_compare_exchange_weak_explicit(
                      volatile A *object, C *expected, C desired,
                      memory_order success, memory_order failure);
        Description

    2   The failure argument shall not be memory_order_release nor
        memory_order_acq_rel. The failure argument shall be no stronger than the
        success argument. Atomically, compares the value pointed to by object for equality
        with that in expected, and if true, replaces the value pointed to by object with
        desired, and if false, updates the value in expected with the value pointed to by
        object. Further, if the comparison is true, memory is affected according to the value of
        success, and if the comparison is false, memory is affected according to the value of
        failure. These operations are atomic read-modify-write operations (5.1.2.4).

    3   NOTE 1    For example, the effect of atomic_compare_exchange_strong is
                 if (memcmp(object, expected, sizeof (*object)) == 0)
                       memcpy(object, &desired, sizeof (*object));
                 else
                       memcpy(expected, object, sizeof (*object));

    4   A weak compare-and-exchange operation may fail spuriously. That is, even when the
        contents of memory referred to by expected and object are equal, it may return zero
        and store back to expected the same memory contents that were originally there.

    5   NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
        machines, e.g. load-locked store-conditional machines.

    6   EXAMPLE         A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
        be in a loop.
                 exp = atomic_load(&cur);
                 do {
                       des = function(exp);
                 } while (!atomic_compare_exchange_weak(&cur, &exp, des));
        When a compare-and-exchange is in a loop, the weak version will yield better performance on some
        platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
        strong one is preferable.

        Returns

    7   The result of the comparison.

### 7.17.7.5 [The atomic_fetch and modify generic functions]

    1   The following operations perform arithmetic and bitwise computations. All of these
        operations are applicable to an object of any atomic integer type. None of these ∗
        operations is applicable to atomic_bool. The key, operator, and computation
        correspondence is:
         key            op          computation
         add            +       addition
         sub            -       subtraction
         or             |       bitwise inclusive or
         xor            ˆ       bitwise exclusive or
         and            &       bitwise and
        Synopsis

    2            #include <stdatomic.h>
                 C atomic_fetch_key(volatile A *object, M operand);
                 C atomic_fetch_key_explicit(volatile A *object,
                      M operand, memory_order order);
        Description

    3   Atomically replaces the value pointed to by object with the result of the computation
        applied to the value pointed to by object and the given operand. Memory is affected
        according to the value of order. These operations are atomic read-modify-write
        operations (5.1.2.4). For signed integer types, arithmetic is defined to use two’s
        complement representation with silent wrap-around on overflow; there are no undefined
        results. For address types, the result may be an undefined address, but the operations
        otherwise have no undefined behavior.
        Returns

    4   Atomically, the value pointed to by object immediately before the effects.

    5   NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
        operation of the corresponding op= compound assignment operators. The only differences are that the
        compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
        compound assignment operator is the updated value of the object, whereas the value returned by the
        atomic_fetch and modify generic functions is the previous value of the atomic object.

### 7.17.8 [Atomic flag type and operations]

    1   The atomic_flag type provides the classic test-and-set functionality. It has two
        states, set and clear.

    2   Operations on an object of type atomic_flag shall be lock free.

    3   NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
        the atomic_flag type is the minimum hardware-implemented type needed to conform to this
        International standard. The remaining types can be emulated with atomic_flag, though with less than
        ideal properties.

    4   The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
        clear state. An atomic_flag that is not explicitly initialized with
        ATOMIC_FLAG_INIT is initially in an indeterminate state.

    5   EXAMPLE
                atomic_flag guard = ATOMIC_FLAG_INIT;

### 7.17.8.1 [The atomic_flag_test_and_set functions]

    1 Synopsis
               #include <stdatomic.h>
                _Bool atomic_flag_test_and_set(
                     volatile atomic_flag *object);
                _Bool atomic_flag_test_and_set_explicit(
                     volatile atomic_flag *object, memory_order order);
        Description

    2   Atomically sets the value pointed to by object to true. Memory is affected according
        to the value of order. These operations are atomic read-modify-write operations
        (5.1.2.4).
        Returns

    3   Atomically, the value of the object immediately before the effects.

### 7.17.8.2 [The atomic_flag_clear functions]

    1 Synopsis
              #include <stdatomic.h>
               void atomic_flag_clear(volatile atomic_flag *object);
               void atomic_flag_clear_explicit(
                    volatile atomic_flag *object, memory_order order);
        Description

    2   The order argument shall not be memory_order_acquire nor
        memory_order_acq_rel. Atomically sets the value pointed to by object to false.
        Memory is affected according to the value of order.
        Returns

    3   The atomic_flag_clear functions return no value.

### 7.18 [Boolean type and values <stdbool.h>]

    1   The header <stdbool.h> defines four macros.

    2   The macro
                 bool
        expands to _Bool.

    3   The remaining three macros are suitable for use in #if preprocessing directives. They
        are
                 true
        which expands to the integer constant 1,
                 false
        which expands to the integer constant 0, and
                 _ _bool_true_false_are_defined
        which expands to the integer constant 1.

    4   Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
        redefine the macros bool, true, and false.[259]

    Footnote 259) See ‘‘future library directions’’ (7.31.9).

### 7.19 [Common definitions <stddef.h>]

    1   The header <stddef.h> defines the following macros and declares the following types.
        Some are also defined in other headers, as noted in their respective subclauses.

    2   The types are
               ptrdiff_t
        which is the signed integer type of the result of subtracting two pointers;
               size_t
        which is the unsigned integer type of the result of the sizeof operator;
               max_align_t
        which is an object type whose alignment is as great as is supported by the implementation
        in all contexts; and
               wchar_t
        which is an integer type whose range of values can represent distinct codes for all
        members of the largest extended character set specified among the supported locales; the
        null character shall have the code value zero. Each member of the basic character set
        shall have a code value equal to its value when used as the lone character in an integer
        character      constant     if     an      implementation      does      not      define
        _ _STDC_MB_MIGHT_NEQ_WC_ _.

    3   The macros are
               NULL
        which expands to an implementation-defined null pointer constant; and
               offsetof(type, member-designator)
        which expands to an integer constant expression that has type size_t, the value of
        which is the offset in bytes, to the structure member (designated by member-designator),
        from the beginning of its structure (designated by type). The type and member designator
        shall be such that given
               static type t;
        then the expression &(t.member-designator) evaluates to an address constant. (If the
        specified member is a bit-field, the behavior is undefined.)
        Recommended practice

    4   The types used for size_t and ptrdiff_t should not have an integer conversion rank
        greater than that of signed long int unless the implementation supports objects
        large enough to make this necessary.                                               ∗

### 7.20 [Integer types <stdint.h>]

    1   The header <stdint.h> declares sets of integer types having specified widths, and
        defines corresponding sets of macros.[260] It also defines macros that specify limits of
        integer types corresponding to types defined in other standard headers.

    Footnote 260) See ‘‘future library directions’’ (7.31.10).

    2   Types are defined in the following categories:
        — integer types having certain exact widths;
        — integer types having at least certain specified widths;
        — fastest integer types having at least certain specified widths;
        — integer types wide enough to hold pointers to objects;
        — integer types having greatest width.
        (Some of these types may denote the same type.)

    3   Corresponding macros specify limits of the declared types and construct suitable
        constants.

    4   For each type described herein that the implementation provides,[261] <stdint.h> shall
        declare that typedef name and define the associated macros. Conversely, for each type
        described herein that the implementation does not provide, <stdint.h> shall not
        declare that typedef name nor shall it define the associated macros. An implementation
        shall provide those types described as ‘‘required’’, but need not provide any of the others
        (described as ‘‘optional’’).

    Footnote 261) Some of these types may denote implementation-defined extended integer types.

### 7.20.1 [Integer types]

    1   When typedef names differing only in the absence or presence of the initial u are defined,
        they shall denote corresponding signed and unsigned types as described in 6.2.5; an
        implementation providing one of these corresponding types shall also provide the other.

    2   In the following descriptions, the symbol N represents an unsigned decimal integer with
        no leading zeros (e.g., 8 or 24, but not 04 or 048).

### 7.20.1.1 [Exact-width integer types]

    1   The typedef name intN_t designates a signed integer type with width N , no padding
        bits, and a two’s complement representation. Thus, int8_t denotes such a signed
        integer type with a width of exactly 8 bits.

    2   The typedef name uintN_t designates an unsigned integer type with width N and no
        padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
        exactly 24 bits.

    3   These types are optional. However, if an implementation provides integer types with
        widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
        two’s complement representation, it shall define the corresponding typedef names.

### 7.20.1.2 [Minimum-width integer types]

    1   The typedef name int_leastN_t designates a signed integer type with a width of at
        least N , such that no signed integer type with lesser size has at least the specified width.
        Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.

    2   The typedef name uint_leastN_t designates an unsigned integer type with a width
        of at least N , such that no unsigned integer type with lesser size has at least the specified
        width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
        least 16 bits.

    3   The following types are required:
                 int_least8_t                                      uint_least8_t
                 int_least16_t                                     uint_least16_t
                 int_least32_t                                     uint_least32_t
                 int_least64_t                                     uint_least64_t
        All other types of this form are optional.

### 7.20.1.3 [Fastest minimum-width integer types]

    1   Each of the following types designates an integer type that is usually fastest[262] to operate
        with among all integer types that have at least the specified width.

    Footnote 262) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
             grounds for choosing one type over another, it will simply pick some integer type satisfying the
             signedness and width requirements.

    2   The typedef name int_fastN_t designates the fastest signed integer type with a width
        of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
        type with a width of at least N .

    3   The following types are required:
               int_fast8_t                             uint_fast8_t
               int_fast16_t                            uint_fast16_t
               int_fast32_t                            uint_fast32_t
               int_fast64_t                            uint_fast64_t
        All other types of this form are optional.

### 7.20.1.4 [Integer types capable of holding object pointers]

    1   The following type designates a signed integer type with the property that any valid
        pointer to void can be converted to this type, then converted back to pointer to void,
        and the result will compare equal to the original pointer:
               intptr_t
        The following type designates an unsigned integer type with the property that any valid
        pointer to void can be converted to this type, then converted back to pointer to void,
        and the result will compare equal to the original pointer:
               uintptr_t
        These types are optional.

### 7.20.1.5 [Greatest-width integer types]

    1   The following type designates a signed integer type capable of representing any value of
        any signed integer type:
               intmax_t
        The following type designates an unsigned integer type capable of representing any value
        of any unsigned integer type:
               uintmax_t
        These types are required.

### 7.20.2 [Limits of specified-width integer types]

    1   The following object-like macros specify the minimum and maximum limits of the types
        declared in <stdint.h>. Each macro name corresponds to a similar type name in
        7.20.1.

    2   Each instance of any defined macro shall be replaced by a constant expression suitable
        for use in #if preprocessing directives, and this expression shall have the same type as
        would an expression that is an object of the corresponding type converted according to
        the integer promotions. Its implementation-defined value shall be equal to or greater in
        magnitude (absolute value) than the corresponding value given below, with the same sign,
        except where stated to be exactly the given value.

### 7.20.2.1 [Limits of exact-width integer types]

    1   — minimum values of exact-width signed integer types
           INTN_MIN                                  exactly −(2 N −1 )
        — maximum values of exact-width signed integer types
           INTN_MAX                                  exactly 2 N −1 − 1
        — maximum values of exact-width unsigned integer types
           UINTN_MAX                                 exactly 2 N − 1

### 7.20.2.2 [Limits of minimum-width integer types]

    1   — minimum values of minimum-width signed integer types
           INT_LEASTN_MIN                                      −(2 N −1 − 1)
        — maximum values of minimum-width signed integer types
           INT_LEASTN_MAX                                      2 N −1 − 1
        — maximum values of minimum-width unsigned integer types
           UINT_LEASTN_MAX                                     2N − 1

### 7.20.2.3 [Limits of fastest minimum-width integer types]

    1   — minimum values of fastest minimum-width signed integer types
           INT_FASTN_MIN                                       −(2 N −1 − 1)
        — maximum values of fastest minimum-width signed integer types
           INT_FASTN_MAX                                       2 N −1 − 1
        — maximum values of fastest minimum-width unsigned integer types
           UINT_FASTN_MAX                                      2N − 1

### 7.20.2.4 [Limits of integer types capable of holding object pointers]

    1   — minimum value of pointer-holding signed integer type
           INTPTR_MIN                                          −(215 − 1)
        — maximum value of pointer-holding signed integer type
           INTPTR_MAX                                          215 − 1
        — maximum value of pointer-holding unsigned integer type
           UINTPTR_MAX                                         216 − 1

### 7.20.2.5 [Limits of greatest-width integer types]

    1   — minimum value of greatest-width signed integer type
            INTMAX_MIN                                                    −(263 − 1)
        — maximum value of greatest-width signed integer type
            INTMAX_MAX                                                    263 − 1
        — maximum value of greatest-width unsigned integer type
            UINTMAX_MAX                                                   264 − 1

### 7.20.3 [Limits of other integer types]

    1   The following object-like macros specify the minimum and maximum limits of integer
        types corresponding to types defined in other standard headers.

    2   Each instance of these macros shall be replaced by a constant expression suitable for use
        in #if preprocessing directives, and this expression shall have the same type as would an
        expression that is an object of the corresponding type converted according to the integer
        promotions. Its implementation-defined value shall be equal to or greater in magnitude
        (absolute value) than the corresponding value given below, with the same sign. An
        implementation shall define only the macros corresponding to those typedef names it
        actually provides.[263]
        — limits of ptrdiff_t
            PTRDIFF_MIN                                                 −65535
            PTRDIFF_MAX                                                 +65535
        — limits of sig_atomic_t
            SIG_ATOMIC_MIN                                              see below
            SIG_ATOMIC_MAX                                              see below
        — limit of size_t
            SIZE_MAX                                                      65535
        — limits of wchar_t
            WCHAR_MIN                                                   see below
            WCHAR_MAX                                                   see below
        — limits of wint_t
            WINT_MIN                                              see below
            WINT_MAX                                              see below

    Footnote 263) A freestanding implementation need not provide all of these types.

    3   If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
        SIG_ATOMIC_MIN shall be no greater than −127 and the value of SIG_ATOMIC_MAX
        shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
        type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
        SIG_ATOMIC_MAX shall be no less than 255.

    4   If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
        shall be no greater than −127 and the value of WCHAR_MAX shall be no less than 127;
        otherwise, wchar_t is defined as an unsigned integer type, and the value of
        WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.[264]

    Footnote 264) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
             character set.

    5   If wint_t (see 7.29) is defined as a signed integer type, the value of WINT_MIN shall
        be no greater than −32767 and the value of WINT_MAX shall be no less than 32767;
        otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
        shall be 0 and the value of WINT_MAX shall be no less than 65535.

### 7.20.4 [Macros for integer constants]

    1   The following function-like macros expand to integer constants suitable for initializing
        objects that have integer types corresponding to types defined in <stdint.h>. Each
        macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.

    2   The argument in any instance of these macros shall be an unsuffixed integer constant (as
        defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.

    3   Each invocation of one of these macros shall expand to an integer constant expression
        suitable for use in #if preprocessing directives. The type of the expression shall have
        the same type as would an expression of the corresponding type converted according to
        the integer promotions. The value of the expression shall be that of the argument.

### 7.20.4.1 [Macros for minimum-width integer constants]

    1   The macro INTN_C(value) shall expand to an integer constant expression
        corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
        to an integer constant expression corresponding to the type uint_leastN_t. For
        example, if uint_least64_t is a name for the type unsigned long long int,
        then UINT64_C(0x123) might expand to the integer constant 0x123ULL.

### 7.20.4.2 [Macros for greatest-width integer constants]

    1   The following macro expands to an integer constant expression having the value specified
        by its argument and the type intmax_t:
               INTMAX_C(value)
        The following macro expands to an integer constant expression having the value specified
        by its argument and the type uintmax_t:
               UINTMAX_C(value)

### 7.21 [Input/output <stdio.h>]

### 7.21.1 [Introduction]

    1   The header <stdio.h> defines several macros, and declares three types and many
        functions for performing input and output.

    2   The types declared are size_t (described in 7.19);
               FILE
        which is an object type capable of recording all the information needed to control a
        stream, including its file position indicator, a pointer to its associated buffer (if any), an
        error indicator that records whether a read/write error has occurred, and an end-of-file
        indicator that records whether the end of the file has been reached; and
               fpos_t
        which is a complete object type other than an array type capable of recording all the
        information needed to specify uniquely every position within a file.

    3   The macros are NULL (described in 7.19);
               _IOFBF
               _IOLBF
               _IONBF
        which expand to integer constant expressions with distinct values, suitable for use as the
        third argument to the setvbuf function;
               BUFSIZ
        which expands to an integer constant expression that is the size of the buffer used by the
        setbuf function;
               EOF
        which expands to an integer constant expression, with type int and a negative value, that
        is returned by several functions to indicate end-of-file, that is, no more input from a
        stream;
               FOPEN_MAX
        which expands to an integer constant expression that is the minimum number of files that
        the implementation guarantees can be open simultaneously;
               FILENAME_MAX
        which expands to an integer constant expression that is the size needed for an array of
        char large enough to hold the longest file name string that the implementation
        guarantees can be opened;[265]
                 L_tmpnam
        which expands to an integer constant expression that is the size needed for an array of
        char large enough to hold a temporary file name string generated by the tmpnam
        function;
                 SEEK_CUR
                 SEEK_END
                 SEEK_SET
        which expand to integer constant expressions with distinct values, suitable for use as the
        third argument to the fseek function;
                 TMP_MAX
        which expands to an integer constant expression that is the minimum number of unique
        file names that can be generated by the tmpnam function;
                 stderr
                 stdin
                 stdout
        which are expressions of type ‘‘pointer to FILE’’ that point to the FILE objects
        associated, respectively, with the standard error, input, and output streams.

    Footnote 265) If the implementation imposes no practical limit on the length of file name strings, the value of
             FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
             string. Of course, file name string contents are subject to other system-specific constraints; therefore
             all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.

    4   The header <wchar.h> declares a number of functions useful for wide character input
        and output. The wide character input/output functions described in that subclause
        provide operations analogous to most of those described here, except that the
        fundamental units internal to the program are wide characters. The external
        representation (in the file) is a sequence of ‘‘generalized’’ multibyte characters, as
        described further in 7.21.3.

    5   The input/output functions are given the following collective terms:
        — The wide character input functions — those functions described in 7.29 that perform
          input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
          fwscanf, wscanf, vfwscanf, and vwscanf.
        — The wide character output functions — those functions described in 7.29 that perform
          output from wide characters and wide strings: fputwc, fputws, putwc,
          putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.
        — The wide character input/output functions — the union of the ungetwc function, the
          wide character input functions, and the wide character output functions.
        — The byte input/output functions — those functions described in this subclause that
          perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
          fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf,
          ungetc, vfprintf, vfscanf, vprintf, and vscanf.
        Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
        tmpnam function (7.21.4.4), <wchar.h> (7.29).

### 7.21.2 [Streams]

    1   Input and output, whether to or from physical devices such as terminals and tape drives,
        or whether to or from files supported on structured storage devices, are mapped into
        logical data streams, whose properties are more uniform than their various inputs and
        outputs. Two forms of mapping are supported, for text streams and for binary
        streams.[266]

    Footnote 266) An implementation need not distinguish between text streams and binary streams. In such an
             implementation, there need be no new-line characters in a text stream nor any limit to the length of a
             line.

    2   A text stream is an ordered sequence of characters composed into lines, each line
        consisting of zero or more characters plus a terminating new-line character. Whether the
        last line requires a terminating new-line character is implementation-defined. Characters
        may have to be added, altered, or deleted on input and output to conform to differing
        conventions for representing text in the host environment. Thus, there need not be a one-
        to-one correspondence between the characters in a stream and those in the external
        representation. Data read in from a text stream will necessarily compare equal to the data
        that were earlier written out to that stream only if: the data consist only of printing
        characters and the control characters horizontal tab and new-line; no new-line character is
        immediately preceded by space characters; and the last character is a new-line character.
        Whether space characters that are written out immediately before a new-line character
        appear when read in is implementation-defined.

    3   A binary stream is an ordered sequence of characters that can transparently record
        internal data. Data read in from a binary stream shall compare equal to the data that were
        earlier written out to that stream, under the same implementation. Such a stream may,
        however, have an implementation-defined number of null characters appended to the end
        of the stream.

    4   Each stream has an orientation. After a stream is associated with an external file, but
        before any operations are performed on it, the stream is without orientation. Once a wide
        character input/output function has been applied to a stream without orientation, the
        stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
        been applied to a stream without orientation, the stream becomes a byte-oriented stream.
        Only a call to the freopen function or the fwide function can otherwise alter the
        orientation of a stream. (A successful call to freopen removes any orientation.)[267]

    Footnote 267) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.

    5   Byte input/output functions shall not be applied to a wide-oriented stream and wide
        character input/output functions shall not be applied to a byte-oriented stream. The
        remaining stream operations do not affect, and are not affected by, a stream’s orientation,
        except for the following additional restrictions:
        — Binary wide-oriented streams have the file-positioning restrictions ascribed to both
          text and binary streams.
        — For wide-oriented streams, after a successful call to a file-positioning function that
          leaves the file position indicator prior to the end-of-file, a wide character output
          function can overwrite a partial multibyte character; any file contents beyond the
          byte(s) written are henceforth indeterminate.

    6   Each wide-oriented stream has an associated mbstate_t object that stores the current
        parse state of the stream. A successful call to fgetpos stores a representation of the
        value of this mbstate_t object as part of the value of the fpos_t object. A later
        successful call to fsetpos using the same stored fpos_t value restores the value of
        the associated mbstate_t object as well as the position within the controlled stream.

    7   Each stream has an associated lock that is used to prevent data races when multiple
        threads of execution access a stream, and to restrict the interleaving of stream operations
        performed by multiple threads. Only one thread may hold this lock at a time. The lock is
        reentrant: a single thread may hold the lock multiple times at a given time.

    8   All functions that read, write, position, or query the position of a stream lock the stream
        before accessing it. They release the lock associated with the stream when the access is
        complete.
        Environmental limits

    9   An implementation shall support text files with lines containing at least 254 characters,
        including the terminating new-line character. The value of the macro BUFSIZ shall be at
        least 256.
        Forward references: the freopen function (7.21.5.4), the fwide function (7.29.3.5),
        mbstate_t (7.30.1), the fgetpos function (7.21.9.1), the fsetpos function
        (7.21.9.3).

### 7.21.3 [Files]

    1   A stream is associated with an external file (which may be a physical device) by opening
        a file, which may involve creating a new file. Creating an existing file causes its former
        contents to be discarded, if necessary. If a file can support positioning requests (such as a
        disk file, as opposed to a terminal), then a file position indicator associated with the
        stream is positioned at the start (character number zero) of the file, unless the file is
        opened with append mode in which case it is implementation-defined whether the file
        position indicator is initially positioned at the beginning or the end of the file. The file
        position indicator is maintained by subsequent reads, writes, and positioning requests, to
        facilitate an orderly progression through the file.

    2   Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
        stream causes the associated file to be truncated beyond that point is implementation-
        defined.

    3   When a stream is unbuffered, characters are intended to appear from the source or at the
        destination as soon as possible. Otherwise characters may be accumulated and
        transmitted to or from the host environment as a block. When a stream is fully buffered,
        characters are intended to be transmitted to or from the host environment as a block when
        a buffer is filled. When a stream is line buffered, characters are intended to be
        transmitted to or from the host environment as a block when a new-line character is
        encountered. Furthermore, characters are intended to be transmitted as a block to the host
        environment when a buffer is filled, when input is requested on an unbuffered stream, or
        when input is requested on a line buffered stream that requires the transmission of
        characters from the host environment. Support for these characteristics is
        implementation-defined, and may be affected via the setbuf and setvbuf functions.

    4   A file may be disassociated from a controlling stream by closing the file. Output streams
        are flushed (any unwritten buffer contents are transmitted to the host environment) before
        the stream is disassociated from the file. The value of a pointer to a FILE object is
        indeterminate after the associated file is closed (including the standard text streams).
        Whether a file of zero length (on which no characters have been written by an output
        stream) actually exists is implementation-defined.

    5   The file may be subsequently reopened, by the same or another program execution, and
        its contents reclaimed or modified (if it can be repositioned at its start). If the main
        function returns to its original caller, or if the exit function is called, all open files are
        closed (hence all output streams are flushed) before program termination. Other paths to
        program termination, such as calling the abort function, need not close all files
        properly.

    6   The address of the FILE object used to control a stream may be significant; a copy of a
        FILE object need not serve in place of the original.

    7    At program startup, three text streams are predefined and need not be opened explicitly
         — standard input (for reading conventional input), standard output (for writing
         conventional output), and standard error (for writing diagnostic output). As initially
         opened, the standard error stream is not fully buffered; the standard input and standard
         output streams are fully buffered if and only if the stream can be determined not to refer
         to an interactive device.

    8    Functions that open additional (nontemporary) files require a file name, which is a string.
         The rules for composing valid file names are implementation-defined. Whether the same
         file can be simultaneously open multiple times is also implementation-defined.

    9    Although both text and binary wide-oriented streams are conceptually sequences of wide
         characters, the external file associated with a wide-oriented stream is a sequence of
         multibyte characters, generalized as follows:
         — Multibyte encodings within files may contain embedded null bytes (unlike multibyte
           encodings valid for use internal to the program).
         — A file need not begin nor end in the initial shift state.[268]

    Footnote 268) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
              undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
              with state-dependent encoding that does not assuredly end in the initial shift state.

    10   Moreover, the encodings used for multibyte characters may differ among files. Both the
         nature and choice of such encodings are implementation-defined.

    11   The wide character input functions read multibyte characters from the stream and convert
         them to wide characters as if they were read by successive calls to the fgetwc function.
         Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
         described by the stream’s own mbstate_t object. The byte input functions read
         characters from the stream as if by successive calls to the fgetc function.

    12   The wide character output functions convert wide characters to multibyte characters and
         write them to the stream as if they were written by successive calls to the fputwc
         function. Each conversion occurs as if by a call to the wcrtomb function, with the
         conversion state described by the stream’s own mbstate_t object. The byte output
         functions write characters to the stream as if by successive calls to the fputc function.

    13   In some cases, some of the byte input/output functions also perform conversions between
         multibyte characters and wide characters. These conversions also occur as if by calls to
         the mbrtowc and wcrtomb functions.

    14   An encoding error occurs if the character sequence presented to the underlying
         mbrtowc function does not form a valid (generalized) multibyte character, or if the code
         value passed to the underlying wcrtomb does not correspond to a valid (generalized)
         multibyte character. The wide character input/output functions and the byte input/output
         functions store the value of the macro EILSEQ in errno if and only if an encoding error
         occurs.
         Environmental limits

    15   The value of FOPEN_MAX shall be at least eight, including the three standard text
         streams.
         Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
         fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
         (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.29.3.1), the
         fputwc function (7.29.3.3), conversion state (7.29.6), the mbrtowc function
         (7.29.6.3.2), the wcrtomb function (7.29.6.3.3).

### 7.21.4 [Operations on files]

### 7.21.4.1 [The remove function]

    1 Synopsis
               #include <stdio.h>
                int remove(const char *filename);
         Description

    2    The remove function causes the file whose name is the string pointed to by filename
         to be no longer accessible by that name. A subsequent attempt to open that file using that
         name will fail, unless it is created anew. If the file is open, the behavior of the remove
         function is implementation-defined.
         Returns

    3    The remove function returns zero if the operation succeeds, nonzero if it fails.

### 7.21.4.2 [The rename function]

    1 Synopsis
               #include <stdio.h>
                int rename(const char *old, const char *new);
         Description

    2    The rename function causes the file whose name is the string pointed to by old to be
         henceforth known by the name given by the string pointed to by new. The file named
         old is no longer accessible by that name. If a file named by the string pointed to by new
         exists prior to the call to the rename function, the behavior is implementation-defined.
        Returns

    3   The rename function returns zero if the operation succeeds, nonzero if it fails,[269] in
        which case if the file existed previously it is still known by its original name.

    Footnote 269) Among the reasons the implementation may cause the rename function to fail are that the file is open
             or that it is necessary to copy its contents to effectuate its renaming.

### 7.21.4.3 [The tmpfile function]

    1 Synopsis
               #include <stdio.h>
                FILE *tmpfile(void);
        Description

    2   The tmpfile function creates a temporary binary file that is different from any other
        existing file and that will automatically be removed when it is closed or at program
        termination. If the program terminates abnormally, whether an open temporary file is
        removed is implementation-defined. The file is opened for update with "wb+" mode.
        Recommended practice

    3   It should be possible to open at least TMP_MAX temporary files during the lifetime of the
        program (this limit may be shared with tmpnam) and there should be no limit on the
        number simultaneously open other than this limit and any limit on the number of open
        files (FOPEN_MAX).
        Returns

    4   The tmpfile function returns a pointer to the stream of the file that it created. If the file
        cannot be created, the tmpfile function returns a null pointer.
        Forward references: the fopen function (7.21.5.3).

### 7.21.4.4 [The tmpnam function]

    1 Synopsis
               #include <stdio.h>
                char *tmpnam(char *s);
        Description

    2   The tmpnam function generates a string that is a valid file name and that is not the same
        as the name of an existing file.[270] The function is potentially capable of generating at
        least TMP_MAX different strings, but any or all of them may already be in use by existing
        files and thus not be suitable return values.

    Footnote 270) Files created using strings generated by the tmpnam function are temporary only in the sense that
             their names should not collide with those generated by conventional naming rules for the
             implementation. It is still necessary to use the remove function to remove such files when their use
             is ended, and before program termination.

    3   The tmpnam function generates a different string each time it is called.

    4   Calls to the tmpnam function with a null pointer argument may introduce data races with
        each other. The implementation shall behave as if no library function calls the tmpnam
        function.
        Returns

    5   If no suitable string can be generated, the tmpnam function returns a null pointer.
        Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
        internal static object and returns a pointer to that object (subsequent calls to the tmpnam
        function may modify the same object). If the argument is not a null pointer, it is assumed
        to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
        in that array and returns the argument as its value.
        Environmental limits

    6   The value of the macro TMP_MAX shall be at least 25.

### 7.21.5 [File access functions]

### 7.21.5.1 [The fclose function]

    1 Synopsis
              #include <stdio.h>
               int fclose(FILE *stream);
        Description

    2   A successful call to the fclose function causes the stream pointed to by stream to be
        flushed and the associated file to be closed. Any unwritten buffered data for the stream
        are delivered to the host environment to be written to the file; any unread buffered data
        are discarded. Whether or not the call succeeds, the stream is disassociated from the file
        and any buffer set by the setbuf or setvbuf function is disassociated from the stream
        (and deallocated if it was automatically allocated).
        Returns

    3   The fclose function returns zero if the stream was successfully closed, or EOF if any
        errors were detected.

### 7.21.5.2 [The fflush function]

    1 Synopsis
               #include <stdio.h>
                int fflush(FILE *stream);
        Description

    2   If stream points to an output stream or an update stream in which the most recent
        operation was not input, the fflush function causes any unwritten data for that stream
        to be delivered to the host environment to be written to the file; otherwise, the behavior is
        undefined.

    3   If stream is a null pointer, the fflush function performs this flushing action on all
        streams for which the behavior is defined above.
        Returns

    4   The fflush function sets the error indicator for the stream and returns EOF if a write
        error occurs, otherwise it returns zero.
        Forward references: the fopen function (7.21.5.3).

### 7.21.5.3 [The fopen function]

    1 Synopsis
               #include <stdio.h>
                FILE *fopen(const char * restrict filename,
                     const char * restrict mode);
        Description

    2   The fopen function opens the file whose name is the string pointed to by filename,
        and associates a stream with it.

    3   The argument mode points to a string. If the string is one of the following, the file is
        open in the indicated mode. Otherwise, the behavior is undefined.[271]
        r                     open text file for reading
        w                     truncate to zero length or create text file for writing
        wx                    create text file for writing
        a                     append; open or create text file for writing at end-of-file
        rb                    open binary file for reading
        wb                    truncate to zero length or create binary file for writing
        wbx          create binary file for writing
        ab           append; open or create binary file for writing at end-of-file
        r+           open text file for update (reading and writing)
        w+           truncate to zero length or create text file for update
        w+x          create text file for update
        a+           append; open or create text file for update, writing at end-of-file
        r+b or rb+   open binary file for update (reading and writing)
        w+b or wb+   truncate to zero length or create binary file for update
        w+bx or wb+x create binary file for update
        a+b or ab+   append; open or create binary file for update, writing at end-of-file

    Footnote 271) If the string begins with one of the above sequences, the implementation might choose to ignore the
             remaining characters, or it might use them to select different kinds of a file (some of which might not
             conform to the properties in 7.21.2).

    4   Opening a file with read mode ('r' as the first character in the mode argument) fails if
        the file does not exist or cannot be read.

    5   Opening a file with exclusive mode ('x' as the last character in the mode argument)
        fails if the file already exists or cannot be created. Otherwise, the file is created with
        exclusive (also known as non-shared) access to the extent that the underlying system
        supports exclusive access.

    6   Opening a file with append mode ('a' as the first character in the mode argument)
        causes all subsequent writes to the file to be forced to the then current end-of-file,
        regardless of intervening calls to the fseek function. In some implementations, opening
        a binary file with append mode ('b' as the second or third character in the above list of
        mode argument values) may initially position the file position indicator for the stream
        beyond the last data written, because of null character padding.

    7   When a file is opened with update mode ('+' as the second or third character in the
        above list of mode argument values), both input and output may be performed on the
        associated stream. However, output shall not be directly followed by input without an
        intervening call to the fflush function or to a file positioning function (fseek,
        fsetpos, or rewind), and input shall not be directly followed by output without an
        intervening call to a file positioning function, unless the input operation encounters end-
        of-file. Opening (or creating) a text file with update mode may instead open (or create) a
        binary stream in some implementations.

    8   When opened, a stream is fully buffered if and only if it can be determined not to refer to
        an interactive device. The error and end-of-file indicators for the stream are cleared.
        Returns

    9   The fopen function returns a pointer to the object controlling the stream. If the open
        operation fails, fopen returns a null pointer.
        Forward references: file positioning functions (7.21.9).

### 7.21.5.4 [The freopen function]

    1 Synopsis
               #include <stdio.h>
                FILE *freopen(const char * restrict filename,
                     const char * restrict mode,
                     FILE * restrict stream);
        Description

    2   The freopen function opens the file whose name is the string pointed to by filename
        and associates the stream pointed to by stream with it. The mode argument is used just
        as in the fopen function.[272]

    Footnote 272) The primary use of the freopen function is to change the file associated with a standard text stream
             (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
             returned by the fopen function may be assigned.

    3   If filename is a null pointer, the freopen function attempts to change the mode of
        the stream to that specified by mode, as if the name of the file currently associated with
        the stream had been used. It is implementation-defined which changes of mode are
        permitted (if any), and under what circumstances.

    4   The freopen function first attempts to close any file that is associated with the specified
        stream. Failure to close the file is ignored. The error and end-of-file indicators for the
        stream are cleared.
        Returns

    5   The freopen function returns a null pointer if the open operation fails. Otherwise,
        freopen returns the value of stream.

### 7.21.5.5 [The setbuf function]

    1 Synopsis
               #include <stdio.h>
                void setbuf(FILE * restrict stream,
                     char * restrict buf);
        Description

    2   Except that it returns no value, the setbuf function is equivalent to the setvbuf
        function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
        is a null pointer), with the value _IONBF for mode.
        Returns

    3   The setbuf function returns no value.
        Forward references: the setvbuf function (7.21.5.6).

### 7.21.5.6 [The setvbuf function]

    1 Synopsis
               #include <stdio.h>
                int setvbuf(FILE * restrict stream,
                     char * restrict buf,
                     int mode, size_t size);
        Description

    2   The setvbuf function may be used only after the stream pointed to by stream has
        been associated with an open file and before any other operation (other than an
        unsuccessful call to setvbuf) is performed on the stream. The argument mode
        determines how stream will be buffered, as follows: _IOFBF causes input/output to be
        fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
        input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
        used instead of a buffer allocated by the setvbuf function[273] and the argument size
        specifies the size of the array; otherwise, size may determine the size of a buffer
        allocated by the setvbuf function. The contents of the array at any time are
        indeterminate.
        Returns

    Footnote 273) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
             before a buffer that has automatic storage duration is deallocated upon block exit.

    3   The setvbuf function returns zero on success, or nonzero if an invalid value is given
        for mode or if the request cannot be honored.

### 7.21.6 [Formatted input/output functions]

    1   The formatted input/output functions shall behave as if there is a sequence point after the
        actions associated with each specifier.[274]

    Footnote 274) The fprintf functions perform writes to memory for the %n specifier.

### 7.21.6.1 [The fprintf function]

    1 Synopsis
                #include <stdio.h>
                 int fprintf(FILE * restrict stream,
                      const char * restrict format, ...);
        Description

    2   The fprintf function writes output to the stream pointed to by stream, under control
        of the string pointed to by format that specifies how subsequent arguments are
        converted for output. If there are insufficient arguments for the format, the behavior is
        undefined. If the format is exhausted while arguments remain, the excess arguments are
        evaluated (as always) but are otherwise ignored. The fprintf function returns when
        the end of the format string is encountered.

    3   The format shall be a multibyte character sequence, beginning and ending in its initial
        shift state. The format is composed of zero or more directives: ordinary multibyte
        characters (not %), which are copied unchanged to the output stream; and conversion
        specifications, each of which results in fetching zero or more subsequent arguments,
        converting them, if applicable, according to the corresponding conversion specifier, and
        then writing the result to the output stream.

    4   Each conversion specification is introduced by the character %. After the %, the following
        appear in sequence:
        — Zero or more flags (in any order) that modify the meaning of the conversion
          specification.
        — An optional minimum field width. If the converted value has fewer characters than the
          field width, it is padded with spaces (by default) on the left (or right, if the left
          adjustment flag, described later, has been given) to the field width. The field width
          takes the form of an asterisk * (described later) or a nonnegative decimal integer.[275]
        — An optional precision that gives the minimum number of digits to appear for the d, i,
          o, u, x, and X conversions, the number of digits to appear after the decimal-point
          character for a, A, e, E, f, and F conversions, the maximum number of significant
          digits for the g and G conversions, or the maximum number of bytes to be written for
            s conversions. The precision takes the form of a period (.) followed either by an
            asterisk * (described later) or by an optional decimal integer; if only the period is
            specified, the precision is taken as zero. If a precision appears with any other
            conversion specifier, the behavior is undefined.
        — An optional length modifier that specifies the size of the argument.
        — A conversion specifier character that specifies the type of conversion to be applied.

    Footnote 275) Note that 0 is taken as a flag, not as the beginning of a field width.

    5   As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
        this case, an int argument supplies the field width or precision. The arguments
        specifying field width, or precision, or both, shall appear (in that order) before the
        argument (if any) to be converted. A negative field width argument is taken as a - flag
        followed by a positive field width. A negative precision argument is taken as if the
        precision were omitted.

    6   The flag characters and their meanings are:
        -        The result of the conversion is left-justified within the field. (It is right-justified if
                 this flag is not specified.)
        +        The result of a signed conversion always begins with a plus or minus sign. (It
                 begins with a sign only when a negative value is converted if this flag is not
                 specified.)[276]
        space If the first character of a signed conversion is not a sign, or if a signed conversion
              results in no characters, a space is prefixed to the result. If the space and + flags
              both appear, the space flag is ignored.
        #        The result is converted to an ‘‘alternative form’’. For o conversion, it increases
                 the precision, if and only if necessary, to force the first digit of the result to be a
                 zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
                 conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
                 and G conversions, the result of converting a floating-point number always
                 contains a decimal-point character, even if no digits follow it. (Normally, a
                 decimal-point character appears in the result of these conversions only if a digit
                 follows it.) For g and G conversions, trailing zeros are not removed from the
                 result. For other conversions, the behavior is undefined.
        0        For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
                 (following any indication of sign or base) are used to pad to the field width rather
                 than performing space padding, except when converting an infinity or NaN. If the
                 0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
                  conversions, if a precision is specified, the 0 flag is ignored. For other
                  conversions, the behavior is undefined.

    Footnote 276) The results of all floating conversions of a negative zero, and of negative values that round to zero,
             include a minus sign.

    7   The length modifiers and their meanings are:
        hh            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                      signed char or unsigned char argument (the argument will have
                      been promoted according to the integer promotions, but its value shall be
                      converted to signed char or unsigned char before printing); or that
                      a following n conversion specifier applies to a pointer to a signed char
                      argument.
        h             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                      short int or unsigned short int argument (the argument will
                      have been promoted according to the integer promotions, but its value shall
                      be converted to short int or unsigned short int before printing);
                      or that a following n conversion specifier applies to a pointer to a short
                      int argument.
        l (ell)       Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                      long int or unsigned long int argument; that a following n
                      conversion specifier applies to a pointer to a long int argument; that a
                      following c conversion specifier applies to a wint_t argument; that a
                      following s conversion specifier applies to a pointer to a wchar_t
                      argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
                      specifier.
        ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                     long long int or unsigned long long int argument; or that a
                     following n conversion specifier applies to a pointer to a long long int
                     argument.
        j             Specifies that a following d, i, o, u, x, or X conversion specifier applies to
                      an intmax_t or uintmax_t argument; or that a following n conversion
                      specifier applies to a pointer to an intmax_t argument.
        z             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                      size_t or the corresponding signed integer type argument; or that a
                      following n conversion specifier applies to a pointer to a signed integer type
                      corresponding to size_t argument.
        t             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                      ptrdiff_t or the corresponding unsigned integer type argument; or that a
                      following n conversion specifier applies to a pointer to a ptrdiff_t
                      argument.
        L              Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                       applies to a long double argument.
        If a length modifier appears with any conversion specifier other than as specified above,
        the behavior is undefined.

    8   The conversion specifiers and their meanings are:
        d,i           The int argument is converted to signed decimal in the style [−]dddd. The
                      precision specifies the minimum number of digits to appear; if the value
                      being converted can be represented in fewer digits, it is expanded with
                      leading zeros. The default precision is 1. The result of converting a zero
                      value with a precision of zero is no characters.
        o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
                decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
                letters abcdef are used for x conversion and the letters ABCDEF for X
                conversion. The precision specifies the minimum number of digits to appear;
                if the value being converted can be represented in fewer digits, it is expanded
                with leading zeros. The default precision is 1. The result of converting a
                zero value with a precision of zero is no characters.
        f,F           A double argument representing a floating-point number is converted to
                      decimal notation in the style [−]ddd.ddd, where the number of digits after
                      the decimal-point character is equal to the precision specification. If the
                      precision is missing, it is taken as 6; if the precision is zero and the # flag is
                      not specified, no decimal-point character appears. If a decimal-point
                      character appears, at least one digit appears before it. The value is rounded to
                      the appropriate number of digits.
                      A double argument representing an infinity is converted in one of the styles
                      [-]inf or [-]infinity — which style is implementation-defined. A
                      double argument representing a NaN is converted in one of the styles
                      [-]nan or [-]nan(n-char-sequence) — which style, and the meaning of
                      any n-char-sequence, is implementation-defined. The F conversion specifier
                      produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
                      respectively.[277]
        e,E           A double argument representing a floating-point number is converted in the
                      style [−]d.ddd e±dd, where there is one digit (which is nonzero if the
                      argument is nonzero) before the decimal-point character and the number of
                      digits after it is equal to the precision; if the precision is missing, it is taken as
                  6; if the precision is zero and the # flag is not specified, no decimal-point
                  character appears. The value is rounded to the appropriate number of digits.
                  The E conversion specifier produces a number with E instead of e
                  introducing the exponent. The exponent always contains at least two digits,
                  and only as many more digits as necessary to represent the exponent. If the
                  value is zero, the exponent is zero.
                  A double argument representing an infinity or NaN is converted in the style
                  of an f or F conversion specifier.
    g,G           A double argument representing a floating-point number is converted in
                  style f or e (or in style F or E in the case of a G conversion specifier),
                  depending on the value converted and the precision. Let P equal the
                  precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
                  Then, if a conversion with style E would have an exponent of X:
                  — if P > X ≥ −4, the conversion is with style f (or F) and precision
                    P − (X + 1).
                  — otherwise, the conversion is with style e (or E) and precision P − 1.
                  Finally, unless the # flag is used, any trailing zeros are removed from the
                  fractional portion of the result and the decimal-point character is removed if
                  there is no fractional portion remaining.
                  A double argument representing an infinity or NaN is converted in the style
                  of an f or F conversion specifier.
    a,A           A double argument representing a floating-point number is converted in the
                  style [−]0xh.hhhh p±d, where there is one hexadecimal digit (which is
                  nonzero if the argument is a normalized floating-point number and is
                  otherwise unspecified) before the decimal-point character[278] and the number
                  of hexadecimal digits after it is equal to the precision; if the precision is
                  missing and FLT_RADIX is a power of 2, then the precision is sufficient for
                  an exact representation of the value; if the precision is missing and
                  FLT_RADIX is not a power of 2, then the precision is sufficient to
                  distinguish[279] values of type double, except that trailing zeros may be
                  omitted; if the precision is zero and the # flag is not specified, no decimal-
                  point character appears. The letters abcdef are used for a conversion and
                  the letters ABCDEF for A conversion. The A conversion specifier produces a
                  number with X and P instead of x and p. The exponent always contains at
                  least one digit, and only as many more digits as necessary to represent the
                  decimal exponent of 2. If the value is zero, the exponent is zero.
                  A double argument representing an infinity or NaN is converted in the style
                  of an f or F conversion specifier.
    c             If no l length modifier is present, the int argument is converted to an
                  unsigned char, and the resulting character is written.
                  If an l length modifier is present, the wint_t argument is converted as if by
                  an ls conversion specification with no precision and an argument that points
                  to the initial element of a two-element array of wchar_t, the first element
                  containing the wint_t argument to the lc conversion specification and the
                  second a null wide character.
    s             If no l length modifier is present, the argument shall be a pointer to the initial
                  element of an array of character type.[280] Characters from the array are
                  written up to (but not including) the terminating null character. If the
                  precision is specified, no more than that many bytes are written. If the
                  precision is not specified or is greater than the size of the array, the array shall
                  contain a null character.
                  If an l length modifier is present, the argument shall be a pointer to the initial
                  element of an array of wchar_t type. Wide characters from the array are
                  converted to multibyte characters (each as if by a call to the wcrtomb
                  function, with the conversion state described by an mbstate_t object
                  initialized to zero before the first wide character is converted) up to and
                  including a terminating null wide character. The resulting multibyte
                  characters are written up to (but not including) the terminating null character
                  (byte). If no precision is specified, the array shall contain a null wide
                  character. If a precision is specified, no more than that many bytes are
                  written (including shift sequences, if any), and the array shall contain a null
                  wide character if, to equal the multibyte character sequence length given by
                        the precision, the function would need to access a wide character one past the
                        end of the array. In no case is a partial multibyte character written.[281]
         p              The argument shall be a pointer to void. The value of the pointer is
                        converted to a sequence of printing characters, in an implementation-defined
                        manner.
         n              The argument shall be a pointer to signed integer into which is written the
                        number of characters written to the output stream so far by this call to
                        fprintf. No argument is converted, but one is consumed. If the conversion
                        specification includes any flags, a field width, or a precision, the behavior is
                        undefined.
         %              A % character is written. No argument is converted. The complete
                        conversion specification shall be %%.

    Footnote 277) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
             the # and 0 flag characters have no effect.

    Footnote 278) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
             that subsequent digits align to nibble (4-bit) boundaries.

    Footnote 279) The precision p is sufficient to distinguish values of the source type if 16 p−1 > b n where b is
             FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
             might suffice depending on the implementation’s scheme for determining the digit to the left of the
             decimal-point character.

    Footnote 280) No special provisions are made for multibyte characters.

    Footnote 281) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.

    9    If a conversion specification is invalid, the behavior is undefined.[282] If any argument is
         not the correct type for the corresponding conversion specification, the behavior is
         undefined.

    Footnote 282) See ‘‘future library directions’’ (7.31.11).

    10   In no case does a nonexistent or small field width cause truncation of a field; if the result
         of a conversion is wider than the field width, the field is expanded to contain the
         conversion result.

    11   For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
         to a hexadecimal floating number with the given precision.
         Recommended practice

    12   For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
         representable in the given precision, the result should be one of the two adjacent numbers
         in hexadecimal floating style with the given precision, with the extra stipulation that the
         error should have a correct sign for the current rounding direction.

    13   For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
         DECIMAL_DIG, then the result should be correctly rounded.[283] If the number of
         significant decimal digits is more than DECIMAL_DIG but the source value is exactly
         representable with DECIMAL_DIG digits, then the result should be an exact
         representation with trailing zeros. Otherwise, the source value is bounded by two
         adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
         of the resultant decimal string D should satisfy L ≤ D ≤ U, with the extra stipulation that
         the error should have a correct sign for the current rounding direction.
         Returns

    Footnote 283) For binary-to-decimal conversion, the result format’s values are the numbers representable with the
              given format specifier. The number of significant digits is determined by the format specifier, and in
              the case of fixed-point conversion by the source value as well.

    14   The fprintf function returns the number of characters transmitted, or a negative value
         if an output or encoding error occurred.
         Environmental limits

    15   The number of characters that can be produced by any single conversion shall be at least
         4095.

    16   EXAMPLE 1         To print a date and time in the form ‘‘Sunday, July 3, 10:02’’ followed by π to five decimal
         places:
                  #include <math.h>
                  #include <stdio.h>
                  /* ... */
                  char *weekday, *month;      // pointers to strings
                  int day, hour, min;
                  fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
                          weekday, month, day, hour, min);
                  fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

    17   EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
         members of the extended character set that consist of more than one byte each consist of exactly two bytes,
         the first of which is denoted here by a and the second by an uppercase letter.

    18   Given the following wide string with length seven,
                  static wchar_t wstr[] = L" X Yabc Z W";
         the seven calls
                  fprintf(stdout, "|1234567890123|\n");
                  fprintf(stdout, "|%13ls|\n", wstr);
                  fprintf(stdout, "|%-13.9ls|\n", wstr);
                  fprintf(stdout, "|%13.10ls|\n", wstr);
                  fprintf(stdout, "|%13.11ls|\n", wstr);
                  fprintf(stdout, "|%13.15ls|\n", &wstr[2]);
                  fprintf(stdout, "|%13lc|\n", (wint_t) wstr[5]);
         will print the following seven lines:
                  |1234567890123|
                  |   X Yabc Z W|
                  | X Yabc Z    |
                  |     X Yabc Z|
                  |   X Yabc Z W|
                  |      abc Z W|
                  |            Z|

         Forward references: conversion state (7.29.6), the wcrtomb function (7.29.6.3.3).

### 7.21.6.2 [The fscanf function]

    1 Synopsis
              #include <stdio.h>
               int fscanf(FILE * restrict stream,
                    const char * restrict format, ...);
        Description

    2   The fscanf function reads input from the stream pointed to by stream, under control
        of the string pointed to by format that specifies the admissible input sequences and how
        they are to be converted for assignment, using subsequent arguments as pointers to the
        objects to receive the converted input. If there are insufficient arguments for the format,
        the behavior is undefined. If the format is exhausted while arguments remain, the excess
        arguments are evaluated (as always) but are otherwise ignored.

    3   The format shall be a multibyte character sequence, beginning and ending in its initial
        shift state. The format is composed of zero or more directives: one or more white-space
        characters, an ordinary multibyte character (neither % nor a white-space character), or a
        conversion specification. Each conversion specification is introduced by the character %.
        After the %, the following appear in sequence:
        — An optional assignment-suppressing character *.
        — An optional decimal integer greater than zero that specifies the maximum field width
          (in characters).
        — An optional length modifier that specifies the size of the receiving object.
        — A conversion specifier character that specifies the type of conversion to be applied.

    4   The fscanf function executes each directive of the format in turn. When all directives
        have been executed, or if a directive fails (as detailed below), the function returns.
        Failures are described as input failures (due to the occurrence of an encoding error or the
        unavailability of input characters), or matching failures (due to inappropriate input).

    5   A directive composed of white-space character(s) is executed by reading input up to the
        first non-white-space character (which remains unread), or until no more characters can
        be read. The directive never fails.

    6   A directive that is an ordinary multibyte character is executed by reading the next
        characters of the stream. If any of those characters differ from the ones composing the
        directive, the directive fails and the differing and subsequent characters remain unread.
        Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
        read, the directive fails.

    7   A directive that is a conversion specification defines a set of matching input sequences, as
        described below for each specifier. A conversion specification is executed in the
         following steps:

    8    Input white-space characters (as specified by the isspace function) are skipped, unless
         the specification includes a [, c, or n specifier.[284]

    Footnote 284) These white-space characters are not counted against a specified field width.

    9    An input item is read from the stream, unless the specification includes an n specifier. An
         input item is defined as the longest sequence of input characters which does not exceed
         any specified field width and which is, or is a prefix of, a matching input sequence.[285]
         The first character, if any, after the input item remains unread. If the length of the input
         item is zero, the execution of the directive fails; this condition is a matching failure unless
         end-of-file, an encoding error, or a read error prevented input from the stream, in which
         case it is an input failure.

    Footnote 285) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
              that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.

    10   Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
         count of input characters) is converted to a type appropriate to the conversion specifier. If
         the input item is not a matching sequence, the execution of the directive fails: this
         condition is a matching failure. Unless assignment suppression was indicated by a *, the
         result of the conversion is placed in the object pointed to by the first argument following
         the format argument that has not already received a conversion result. If this object
         does not have an appropriate type, or if the result of the conversion cannot be represented
         in the object, the behavior is undefined.

    11   The length modifiers and their meanings are:
         hh             Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                        to an argument with type pointer to signed char or unsigned char.
         h              Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                        to an argument with type pointer to short int or unsigned short
                        int.
         l (ell)        Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                        to an argument with type pointer to long int or unsigned long
                        int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
                        an argument with type pointer to double; or that a following c, s, or [
                        conversion specifier applies to an argument with type pointer to wchar_t.
         ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to long long int or unsigned
                      long long int.
         j           Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                     to an argument with type pointer to intmax_t or uintmax_t.
         z           Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                     to an argument with type pointer to size_t or the corresponding signed
                     integer type.
         t           Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                     to an argument with type pointer to ptrdiff_t or the corresponding
                     unsigned integer type.
         L           Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                     applies to an argument with type pointer to long double.
         If a length modifier appears with any conversion specifier other than as specified above,
         the behavior is undefined.

    12   The conversion specifiers and their meanings are:
         d          Matches an optionally signed decimal integer, whose format is the same as
                    expected for the subject sequence of the strtol function with the value 10
                    for the base argument. The corresponding argument shall be a pointer to
                    signed integer.
         i          Matches an optionally signed integer, whose format is the same as expected
                    for the subject sequence of the strtol function with the value 0 for the
                    base argument. The corresponding argument shall be a pointer to signed
                    integer.
         o          Matches an optionally signed octal integer, whose format is the same as
                    expected for the subject sequence of the strtoul function with the value 8
                    for the base argument. The corresponding argument shall be a pointer to
                    unsigned integer.
         u          Matches an optionally signed decimal integer, whose format is the same as
                    expected for the subject sequence of the strtoul function with the value 10
                    for the base argument. The corresponding argument shall be a pointer to
                    unsigned integer.
         x          Matches an optionally signed hexadecimal integer, whose format is the same
                    as expected for the subject sequence of the strtoul function with the value
                    16 for the base argument. The corresponding argument shall be a pointer to
                    unsigned integer.
         a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
                 format is the same as expected for the subject sequence of the strtod
                 function. The corresponding argument shall be a pointer to floating.
    c             Matches a sequence of characters of exactly the number specified by the field
                  width (1 if no field width is present in the directive).[286]
                  If no l length modifier is present, the corresponding argument shall be a
                  pointer to the initial element of a character array large enough to accept the
                  sequence. No null character is added.
                  If an l length modifier is present, the input shall be a sequence of multibyte
                  characters that begins in the initial shift state. Each multibyte character in the
                  sequence is converted to a wide character as if by a call to the mbrtowc
                  function, with the conversion state described by an mbstate_t object
                  initialized to zero before the first multibyte character is converted. The
                  corresponding argument shall be a pointer to the initial element of an array of
                  wchar_t large enough to accept the resulting sequence of wide characters.
                  No null wide character is added.
    s             Matches a sequence of non-white-space characters.[286]
                  If no l length modifier is present, the corresponding argument shall be a
                  pointer to the initial element of a character array large enough to accept the
                  sequence and a terminating null character, which will be added automatically.
                  If an l length modifier is present, the input shall be a sequence of multibyte
                  characters that begins in the initial shift state. Each multibyte character is
                  converted to a wide character as if by a call to the mbrtowc function, with
                  the conversion state described by an mbstate_t object initialized to zero
                  before the first multibyte character is converted. The corresponding argument
                  shall be a pointer to the initial element of an array of wchar_t large enough
                  to accept the sequence and the terminating null wide character, which will be
                  added automatically.
    [             Matches a nonempty sequence of characters from a set of expected characters
                  (the scanset).[286]
                  If no l length modifier is present, the corresponding argument shall be a
                  pointer to the initial element of a character array large enough to accept the
                  sequence and a terminating null character, which will be added automatically.
                  If an l length modifier is present, the input shall be a sequence of multibyte
                  characters that begins in the initial shift state. Each multibyte character is
                  converted to a wide character as if by a call to the mbrtowc function, with
                  the conversion state described by an mbstate_t object initialized to zero
                        before the first multibyte character is converted. The corresponding argument
                        shall be a pointer to the initial element of an array of wchar_t large enough
                        to accept the sequence and the terminating null wide character, which will be
                        added automatically.
                        The conversion specifier includes all subsequent characters in the format
                        string, up to and including the matching right bracket (]). The characters
                        between the brackets (the scanlist) compose the scanset, unless the character
                        after the left bracket is a circumflex (^), in which case the scanset contains all
                        characters that do not appear in the scanlist between the circumflex and the
                        right bracket. If the conversion specifier begins with [] or [^], the right
                        bracket character is in the scanlist and the next following right bracket
                        character is the matching right bracket that ends the specification; otherwise
                        the first following right bracket character is the one that ends the
                        specification. If a - character is in the scanlist and is not the first, nor the
                        second where the first character is a ^, nor the last character, the behavior is
                        implementation-defined.
         p              Matches an implementation-defined set of sequences, which should be the
                        same as the set of sequences that may be produced by the %p conversion of
                        the fprintf function. The corresponding argument shall be a pointer to a
                        pointer to void. The input item is converted to a pointer value in an
                        implementation-defined manner. If the input item is a value converted earlier
                        during the same program execution, the pointer that results shall compare
                        equal to that value; otherwise the behavior of the %p conversion is undefined.
         n              No input is consumed. The corresponding argument shall be a pointer to
                        signed integer into which is to be written the number of characters read from
                        the input stream so far by this call to the fscanf function. Execution of a
                        %n directive does not increment the assignment count returned at the
                        completion of execution of the fscanf function. No argument is converted,
                        but one is consumed. If the conversion specification includes an assignment-
                        suppressing character or a field width, the behavior is undefined.
         %              Matches a single % character; no conversion or assignment occurs. The
                        complete conversion specification shall be %%.

    Footnote 286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
         conversion specifiers — the extent of the input field is determined on a byte-by-byte basis. The
         resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.

    Footnote 286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
         conversion specifiers — the extent of the input field is determined on a byte-by-byte basis. The
         resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.

    Footnote 286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
         conversion specifiers — the extent of the input field is determined on a byte-by-byte basis. The
         resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.

    13   If a conversion specification is invalid, the behavior is undefined.[287]

    Footnote 287) See ‘‘future library directions’’ (7.31.11).

    14   The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
         respectively, a, e, f, g, and x.

    15   Trailing white space (including new-line characters) is left unread unless matched by a
         directive. The success of literal matches and suppressed assignments is not directly
         determinable other than via the %n directive.
         Returns

    16   The fscanf function returns the value of the macro EOF if an input failure occurs
         before the first conversion (if any) has completed. Otherwise, the function returns the
         number of input items assigned, which can be fewer than provided for, or even zero, in
         the event of an early matching failure.

    17   EXAMPLE 1        The call:
                  #include <stdio.h>
                  /* ... */
                  int n, i; float x; char name[50];
                  n = fscanf(stdin, "%d%f%s", &i, &x, name);
         with the input line:
                  25 54.32E-1 thompson
         will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
         thompson\0.

    18   EXAMPLE 2        The call:
                  #include <stdio.h>
                  /* ... */
                  int i; float x; char name[50];
                  fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
         with input:
                  56789 0123 56a72
         will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the
         sequence 56\0. The next character read from the input stream will be a.

    19   EXAMPLE 3        To accept repeatedly from stdin a quantity, a unit of measure, and an item name:
                  #include <stdio.h>
                  /* ... */
                  int count; float quant; char units[21], item[21];
                  do {
                          count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
                          fscanf(stdin,"%*[^\n]");
                  } while (!feof(stdin) && !ferror(stdin));

    20   If the stdin stream contains the following lines:
                  2 quarts of oil
                  -12.8degrees Celsius
                  lots of luck
                  10.0LBS     of
                  dirt
                  100ergs of energy
         the execution of the above example will be analogous to the following assignments:
                   quant = 2; strcpy(units, "quarts"); strcpy(item, "oil");
                   count = 3;
                   quant = -12.8; strcpy(units, "degrees");
                   count = 2; // "C" fails to match "o"
                   count = 0; // "l" fails to match "%f"
                   quant = 10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
                   count = 3;
                   count = 0; // "100e" fails to match "%f"
                   count = EOF;

    21   EXAMPLE 4         In:
                   #include <stdio.h>
                   /* ... */
                   int d1, d2, n1, n2, i;
                   i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
         the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure, the value
         of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.

    22   EXAMPLE 5         The call:
                   #include <stdio.h>
                   /* ... */
                   int n, i;
                   n = sscanf("foo %            bar    42", "foo%%bar%d", &i);
         will assign to n the value 1 and to i the value 42 because input white-space characters are skipped for both
         the % and d conversion specifiers.

    23   EXAMPLE 6 In these examples, multibyte characters do have a state-dependent encoding, and the
         members of the extended character set that consist of more than one byte each consist of exactly two bytes,
         the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as
         such when in the alternate shift state. The shift sequences are denoted by ↑ and ↓, in which the first causes
         entry into the alternate shift state.

    24   After the call:
                   #include <stdio.h>
                   /* ... */
                   char str[50];
                   fscanf(stdin, "a%s", str);
         with the input line:
                   a↑ X Y↓ bc
         str will contain ↑ X Y↓\0 assuming that none of the bytes of the shift sequences (or of the multibyte
         characters, in the more general case) appears to be a single-byte white-space character.

    25   In contrast, after the call:
                 #include <stdio.h>
                 #include <stddef.h>
                 /* ... */
                 wchar_t wstr[50];
                 fscanf(stdin, "a%ls", wstr);
         with the same input line, wstr will contain the two wide characters that correspond to X and Y and a
         terminating null wide character.

    26   However, the call:
                 #include <stdio.h>
                 #include <stddef.h>
                 /* ... */
                 wchar_t wstr[50];
                 fscanf(stdin, "a↑ X↓%ls", wstr);
         with the same input line will return zero due to a matching failure against the ↓ sequence in the format
         string.

    27   Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
         character Y, after the call:
                 #include <stdio.h>
                 #include <stddef.h>
                 /* ... */
                 wchar_t wstr[50];
                 fscanf(stdin, "a↑ Y↓%ls", wstr);
         with the same input line, zero will again be returned, but stdin will be left with a partially consumed
         multibyte character.

         Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the
         strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state
         (7.29.6), the wcrtomb function (7.29.6.3.3).

### 7.21.6.3 [The printf function]

    1 Synopsis
                #include <stdio.h>
                 int printf(const char * restrict format, ...);
         Description

    2    The printf function is equivalent to fprintf with the argument stdout interposed
         before the arguments to printf.
         Returns

    3    The printf function returns the number of characters transmitted, or a negative value if
         an output or encoding error occurred.

### 7.21.6.4 [The scanf function]

    1 Synopsis
              #include <stdio.h>
               int scanf(const char * restrict format, ...);
        Description

    2   The scanf function is equivalent to fscanf with the argument stdin interposed
        before the arguments to scanf.
        Returns

    3   The scanf function returns the value of the macro EOF if an input failure occurs before
        the first conversion (if any) has completed. Otherwise, the scanf function returns the
        number of input items assigned, which can be fewer than provided for, or even zero, in
        the event of an early matching failure.

### 7.21.6.5 [The snprintf function]

    1 Synopsis
              #include <stdio.h>
               int snprintf(char * restrict s, size_t n,
                    const char * restrict format, ...);
        Description

    2   The snprintf function is equivalent to fprintf, except that the output is written into
        an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
        and s may be a null pointer. Otherwise, output characters beyond the n-1st are
        discarded rather than being written to the array, and a null character is written at the end
        of the characters actually written into the array. If copying takes place between objects
        that overlap, the behavior is undefined.
        Returns

    3   The snprintf function returns the number of characters that would have been written
        had n been sufficiently large, not counting the terminating null character, or a negative
        value if an encoding error occurred. Thus, the null-terminated output has been
        completely written if and only if the returned value is nonnegative and less than n.

### 7.21.6.6 [The sprintf function]

    1 Synopsis
              #include <stdio.h>
               int sprintf(char * restrict s,
                    const char * restrict format, ...);
        Description

    2   The sprintf function is equivalent to fprintf, except that the output is written into
        an array (specified by the argument s) rather than to a stream. A null character is written
        at the end of the characters written; it is not counted as part of the returned value. If
        copying takes place between objects that overlap, the behavior is undefined.
        Returns

    3   The sprintf function returns the number of characters written in the array, not
        counting the terminating null character, or a negative value if an encoding error occurred.

### 7.21.6.7 [The sscanf function]

    1 Synopsis
              #include <stdio.h>
               int sscanf(const char * restrict s,
                    const char * restrict format, ...);
        Description

    2   The sscanf function is equivalent to fscanf, except that input is obtained from a
        string (specified by the argument s) rather than from a stream. Reaching the end of the
        string is equivalent to encountering end-of-file for the fscanf function. If copying
        takes place between objects that overlap, the behavior is undefined.
        Returns

    3   The sscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the sscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.21.6.8 [The vfprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               int vfprintf(FILE * restrict stream,
                    const char * restrict format,
                    va_list arg);
        Description

    2   The vfprintf function is equivalent to fprintf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vfprintf function does not invoke the
        va_end macro.[288]
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vfprintf function returns the number of characters transmitted, or a negative
        value if an output or encoding error occurred.

    4   EXAMPLE       The following shows the use of the vfprintf function in a general error-reporting routine.
               #include <stdarg.h>
               #include <stdio.h>
               void error(char *function_name, char *format, ...)
               {
                     va_list args;
                        va_start(args, format);
                        // print out name of function causing error
                        fprintf(stderr, "ERROR in %s: ", function_name);
                        // print out remainder of message
                        vfprintf(stderr, format, args);
                        va_end(args);
               }

### 7.21.6.9 [The vfscanf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               int vfscanf(FILE * restrict stream,
                    const char * restrict format,
                    va_list arg);
        Description

    2   The vfscanf function is equivalent to fscanf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vfscanf function does not invoke the
        va_end macro.[288]
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vfscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the vfscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.21.6.10 [The vprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               int vprintf(const char * restrict format,
                    va_list arg);
        Description

    2   The vprintf function is equivalent to printf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vprintf function does not invoke the
        va_end macro.[288]
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vprintf function returns the number of characters transmitted, or a negative value
        if an output or encoding error occurred.

### 7.21.6.11 [The vscanf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               int vscanf(const char * restrict format,
                    va_list arg);
        Description

    2   The vscanf function is equivalent to scanf, with the variable argument list replaced
        by arg, which shall have been initialized by the va_start macro (and possibly
        subsequent va_arg calls). The vscanf function does not invoke the va_end
        macro.[288]
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the vscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.21.6.12 [The vsnprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               int vsnprintf(char * restrict s, size_t n,
                    const char * restrict format,
                    va_list arg);
        Description

    2   The vsnprintf function is equivalent to snprintf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vsnprintf function does not invoke the
        va_end macro.[288] If copying takes place between objects that overlap, the behavior is
        undefined.
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vsnprintf function returns the number of characters that would have been written
        had n been sufficiently large, not counting the terminating null character, or a negative
        value if an encoding error occurred. Thus, the null-terminated output has been
        completely written if and only if the returned value is nonnegative and less than n.

### 7.21.6.13 [The vsprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               int vsprintf(char * restrict s,
                    const char * restrict format,
                    va_list arg);
        Description

    2   The vsprintf function is equivalent to sprintf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vsprintf function does not invoke the
        va_end macro.[288] If copying takes place between objects that overlap, the behavior is
        undefined.
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vsprintf function returns the number of characters written in the array, not
        counting the terminating null character, or a negative value if an encoding error occurred.

### 7.21.6.14 [The vsscanf function]

    1 Synopsis
               #include <stdarg.h>
                #include <stdio.h>
                int vsscanf(const char * restrict s,
                     const char * restrict format,
                     va_list arg);
        Description

    2   The vsscanf function is equivalent to sscanf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vsscanf function does not invoke the
        va_end macro.[288]
        Returns

    Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
             vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vsscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the vsscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.21.7 [Character input/output functions]

### 7.21.7.1 [The fgetc function]

    1 Synopsis
               #include <stdio.h>
                int fgetc(FILE *stream);
        Description

    2   If the end-of-file indicator for the input stream pointed to by stream is not set and a
        next character is present, the fgetc function obtains that character as an unsigned
        char converted to an int and advances the associated file position indicator for the
        stream (if defined).
        Returns

    3   If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
        of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
        fgetc function returns the next character from the input stream pointed to by stream.
        If a read error occurs, the error indicator for the stream is set and the fgetc function
        returns EOF.[289]

    Footnote 289) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.

### 7.21.7.2 [The fgets function]

    1 Synopsis
              #include <stdio.h>
               char *fgets(char * restrict s, int n,
                    FILE * restrict stream);
        Description

    2   The fgets function reads at most one less than the number of characters specified by n
        from the stream pointed to by stream into the array pointed to by s. No additional
        characters are read after a new-line character (which is retained) or after end-of-file. A
        null character is written immediately after the last character read into the array.
        Returns

    3   The fgets function returns s if successful. If end-of-file is encountered and no
        characters have been read into the array, the contents of the array remain unchanged and a
        null pointer is returned. If a read error occurs during the operation, the array contents are
        indeterminate and a null pointer is returned.

### 7.21.7.3 [The fputc function]

    1 Synopsis
              #include <stdio.h>
               int fputc(int c, FILE *stream);
        Description

    2   The fputc function writes the character specified by c (converted to an unsigned
        char) to the output stream pointed to by stream, at the position indicated by the
        associated file position indicator for the stream (if defined), and advances the indicator
        appropriately. If the file cannot support positioning requests, or if the stream was opened
        with append mode, the character is appended to the output stream.
        Returns

    3   The fputc function returns the character written. If a write error occurs, the error
        indicator for the stream is set and fputc returns EOF.

### 7.21.7.4 [The fputs function]

    1 Synopsis
              #include <stdio.h>
               int fputs(const char * restrict s,
                    FILE * restrict stream);
        Description

    2   The fputs function writes the string pointed to by s to the stream pointed to by
        stream. The terminating null character is not written.
        Returns

    3   The fputs function returns EOF if a write error occurs; otherwise it returns a
        nonnegative value.

### 7.21.7.5 [The getc function]

    1 Synopsis
              #include <stdio.h>
               int getc(FILE *stream);
        Description

    2   The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
        may evaluate stream more than once, so the argument should never be an expression
        with side effects.
        Returns

    3   The getc function returns the next character from the input stream pointed to by
        stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
        getc returns EOF. If a read error occurs, the error indicator for the stream is set and
        getc returns EOF.

### 7.21.7.6 [The getchar function]

    1 Synopsis
              #include <stdio.h>
               int getchar(void);
        Description

    2   The getchar function is equivalent to getc with the argument stdin.
        Returns

    3   The getchar function returns the next character from the input stream pointed to by
        stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
        getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
        getchar returns EOF.

### 7.21.7.7 [The putc function]

    1 Synopsis
              #include <stdio.h>
               int putc(int c, FILE *stream);
        Description

    2   The putc function is equivalent to fputc, except that if it is implemented as a macro, it
        may evaluate stream more than once, so that argument should never be an expression
        with side effects.
        Returns

    3   The putc function returns the character written. If a write error occurs, the error
        indicator for the stream is set and putc returns EOF.

### 7.21.7.8 [The putchar function]

    1 Synopsis
              #include <stdio.h>
               int putchar(int c);
        Description

    2   The putchar function is equivalent to putc with the second argument stdout.
        Returns

    3   The putchar function returns the character written. If a write error occurs, the error
        indicator for the stream is set and putchar returns EOF.

### 7.21.7.9 [The puts function]

    1 Synopsis
              #include <stdio.h>
               int puts(const char *s);
        Description

    2   The puts function writes the string pointed to by s to the stream pointed to by stdout,
        and appends a new-line character to the output. The terminating null character is not
        written.
        Returns

    3   The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
        value.

### 7.21.7.10 [The ungetc function]

    1 Synopsis
                #include <stdio.h>
                 int ungetc(int c, FILE *stream);
        Description

    2   The ungetc function pushes the character specified by c (converted to an unsigned
        char) back onto the input stream pointed to by stream. Pushed-back characters will be
        returned by subsequent reads on that stream in the reverse order of their pushing. A
        successful intervening call (with the stream pointed to by stream) to a file positioning
        function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
        stream. The external storage corresponding to the stream is unchanged.

    3   One character of pushback is guaranteed. If the ungetc function is called too many
        times on the same stream without an intervening read or file positioning operation on that
        stream, the operation may fail.

    4   If the value of c equals that of the macro EOF, the operation fails and the input stream is
        unchanged.

    5   A successful call to the ungetc function clears the end-of-file indicator for the stream.
        The value of the file position indicator for the stream after reading or discarding all
        pushed-back characters shall be the same as it was before the characters were pushed
        back. For a text stream, the value of its file position indicator after a successful call to the
        ungetc function is unspecified until all pushed-back characters are read or discarded.
        For a binary stream, its file position indicator is decremented by each successful call to
        the ungetc function; if its value was zero before a call, it is indeterminate after the
        call.[290]
        Returns

    Footnote 290) See ‘‘future library directions’’ (7.31.11).

    6   The ungetc function returns the character pushed back after conversion, or EOF if the
        operation fails.
        Forward references: file positioning functions (7.21.9).

### 7.21.8 [Direct input/output functions]

### 7.21.8.1 [The fread function]

    1 Synopsis
              #include <stdio.h>
               size_t fread(void * restrict ptr,
                    size_t size, size_t nmemb,
                    FILE * restrict stream);
        Description

    2   The fread function reads, into the array pointed to by ptr, up to nmemb elements
        whose size is specified by size, from the stream pointed to by stream. For each
        object, size calls are made to the fgetc function and the results stored, in the order
        read, in an array of unsigned char exactly overlaying the object. The file position
        indicator for the stream (if defined) is advanced by the number of characters successfully
        read. If an error occurs, the resulting value of the file position indicator for the stream is
        indeterminate. If a partial element is read, its value is indeterminate.
        Returns

    3   The fread function returns the number of elements successfully read, which may be
        less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
        fread returns zero and the contents of the array and the state of the stream remain
        unchanged.

### 7.21.8.2 [The fwrite function]

    1 Synopsis
              #include <stdio.h>
               size_t fwrite(const void * restrict ptr,
                    size_t size, size_t nmemb,
                    FILE * restrict stream);
        Description

    2   The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
        whose size is specified by size, to the stream pointed to by stream. For each object,
        size calls are made to the fputc function, taking the values (in order) from an array of
        unsigned char exactly overlaying the object. The file position indicator for the
        stream (if defined) is advanced by the number of characters successfully written. If an
        error occurs, the resulting value of the file position indicator for the stream is
        indeterminate.
        Returns

    3   The fwrite function returns the number of elements successfully written, which will be
        less than nmemb only if a write error is encountered. If size or nmemb is zero,
        fwrite returns zero and the state of the stream remains unchanged.

### 7.21.9 [File positioning functions]

### 7.21.9.1 [The fgetpos function]

    1 Synopsis
              #include <stdio.h>
               int fgetpos(FILE * restrict stream,
                    fpos_t * restrict pos);
        Description

    2   The fgetpos function stores the current values of the parse state (if any) and file
        position indicator for the stream pointed to by stream in the object pointed to by pos.
        The values stored contain unspecified information usable by the fsetpos function for
        repositioning the stream to its position at the time of the call to the fgetpos function.
        Returns

    3   If successful, the fgetpos function returns zero; on failure, the fgetpos function
        returns nonzero and stores an implementation-defined positive value in errno.
        Forward references: the fsetpos function (7.21.9.3).

### 7.21.9.2 [The fseek function]

    1 Synopsis
              #include <stdio.h>
               int fseek(FILE *stream, long int offset, int whence);
        Description

    2   The fseek function sets the file position indicator for the stream pointed to by stream.
        If a read or write error occurs, the error indicator for the stream is set and fseek fails.

    3   For a binary stream, the new position, measured in characters from the beginning of the
        file, is obtained by adding offset to the position specified by whence. The specified
        position is the beginning of the file if whence is SEEK_SET, the current value of the file
        position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
        meaningfully support fseek calls with a whence value of SEEK_END.

    4   For a text stream, either offset shall be zero, or offset shall be a value returned by
        an earlier successful call to the ftell function on a stream associated with the same file
        and whence shall be SEEK_SET.

    5   After determining the new position, a successful call to the fseek function undoes any
        effects of the ungetc function on the stream, clears the end-of-file indicator for the
        stream, and then establishes the new position. After a successful fseek call, the next
        operation on an update stream may be either input or output.
        Returns

    6   The fseek function returns nonzero only for a request that cannot be satisfied.
        Forward references: the ftell function (7.21.9.4).

### 7.21.9.3 [The fsetpos function]

    1 Synopsis
              #include <stdio.h>
               int fsetpos(FILE *stream, const fpos_t *pos);
        Description

    2   The fsetpos function sets the mbstate_t object (if any) and file position indicator
        for the stream pointed to by stream according to the value of the object pointed to by
        pos, which shall be a value obtained from an earlier successful call to the fgetpos
        function on a stream associated with the same file. If a read or write error occurs, the
        error indicator for the stream is set and fsetpos fails.

    3   A successful call to the fsetpos function undoes any effects of the ungetc function
        on the stream, clears the end-of-file indicator for the stream, and then establishes the new
        parse state and position. After a successful fsetpos call, the next operation on an
        update stream may be either input or output.
        Returns

    4   If successful, the fsetpos function returns zero; on failure, the fsetpos function
        returns nonzero and stores an implementation-defined positive value in errno.

### 7.21.9.4 [The ftell function]

    1 Synopsis
              #include <stdio.h>
               long int ftell(FILE *stream);
        Description

    2   The ftell function obtains the current value of the file position indicator for the stream
        pointed to by stream. For a binary stream, the value is the number of characters from
        the beginning of the file. For a text stream, its file position indicator contains unspecified
        information, usable by the fseek function for returning the file position indicator for the
        stream to its position at the time of the ftell call; the difference between two such
        return values is not necessarily a meaningful measure of the number of characters written
        or read.
        Returns

    3   If successful, the ftell function returns the current value of the file position indicator
        for the stream. On failure, the ftell function returns −1L and stores an
        implementation-defined positive value in errno.

### 7.21.9.5 [The rewind function]

    1 Synopsis
              #include <stdio.h>
               void rewind(FILE *stream);
        Description

    2   The rewind function sets the file position indicator for the stream pointed to by
        stream to the beginning of the file. It is equivalent to
               (void)fseek(stream, 0L, SEEK_SET)
        except that the error indicator for the stream is also cleared.
        Returns

    3   The rewind function returns no value.

### 7.21.10 [Error-handling functions]

### 7.21.10.1 [The clearerr function]

    1 Synopsis
              #include <stdio.h>
               void clearerr(FILE *stream);
        Description

    2   The clearerr function clears the end-of-file and error indicators for the stream pointed
        to by stream.
        Returns

    3   The clearerr function returns no value.

### 7.21.10.2 [The feof function]

    1 Synopsis
              #include <stdio.h>
               int feof(FILE *stream);
        Description

    2   The feof function tests the end-of-file indicator for the stream pointed to by stream.
        Returns

    3   The feof function returns nonzero if and only if the end-of-file indicator is set for
        stream.

### 7.21.10.3 [The ferror function]

    1 Synopsis
              #include <stdio.h>
               int ferror(FILE *stream);
        Description

    2   The ferror function tests the error indicator for the stream pointed to by stream.
        Returns

    3   The ferror function returns nonzero if and only if the error indicator is set for
        stream.

### 7.21.10.4 [The perror function]

    1 Synopsis
              #include <stdio.h>
               void perror(const char *s);
        Description

    2   The perror function maps the error number in the integer expression errno to an
        error message. It writes a sequence of characters to the standard error stream thus: first
        (if s is not a null pointer and the character pointed to by s is not the null character), the
        string pointed to by s followed by a colon (:) and a space; then an appropriate error
        message string followed by a new-line character. The contents of the error message
        strings are the same as those returned by the strerror function with argument errno.
        Returns

    3   The perror function returns no value.
        Forward references: the strerror function (7.24.6.2).

### 7.22 [General utilities <stdlib.h>]

    1   The header <stdlib.h> declares five types and several functions of general utility, and
        defines several macros.[291]

    Footnote 291) See ‘‘future library directions’’ (7.31.12).

    2   The types declared are size_t and wchar_t (both described in 7.19),
                 div_t
        which is a structure type that is the type of the value returned by the div function,
                 ldiv_t
        which is a structure type that is the type of the value returned by the ldiv function, and
                 lldiv_t
        which is a structure type that is the type of the value returned by the lldiv function.

    3   The macros defined are NULL (described in 7.19);
                 EXIT_FAILURE
        and
                 EXIT_SUCCESS
        which expand to integer constant expressions that can be used as the argument to the
        exit function to return unsuccessful or successful termination status, respectively, to the
        host environment;
                 RAND_MAX
        which expands to an integer constant expression that is the maximum value returned by
        the rand function; and
                 MB_CUR_MAX
        which expands to a positive integer expression with type size_t that is the maximum
        number of bytes in a multibyte character for the extended character set specified by the
        current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.

### 7.22.1 [Numeric conversion functions]

    1   The functions atof, atoi, atol, and atoll need not affect the value of the integer
        expression errno on an error. If the value of the result cannot be represented, the
        behavior is undefined.

### 7.22.1.1 [The atof function]

    1 Synopsis
              #include <stdlib.h>
               double atof(const char *nptr);
        Description

    2   The atof function converts the initial portion of the string pointed to by nptr to
        double representation. Except for the behavior on error, it is equivalent to
               strtod(nptr, (char **)NULL)
        Returns

    3   The atof function returns the converted value.
        Forward references: the strtod, strtof, and strtold functions (7.22.1.3).

### 7.22.1.2 [The atoi, atol, and atoll functions]

    1 Synopsis
              #include <stdlib.h>
               int atoi(const char *nptr);
               long int atol(const char *nptr);
               long long int atoll(const char *nptr);
        Description

    2   The atoi, atol, and atoll functions convert the initial portion of the string pointed
        to by nptr to int, long int, and long long int representation, respectively.
        Except for the behavior on error, they are equivalent to
               atoi: (int)strtol(nptr, (char **)NULL, 10)
               atol: strtol(nptr, (char **)NULL, 10)
               atoll: strtoll(nptr, (char **)NULL, 10)
        Returns

    3   The atoi, atol, and atoll functions return the converted value.
        Forward references: the strtol, strtoll, strtoul, and strtoull functions
        (7.22.1.4).

### 7.22.1.3 [The strtod, strtof, and strtold functions]

    1 Synopsis
              #include <stdlib.h>
               double strtod(const char * restrict nptr,
                    char ** restrict endptr);
               float strtof(const char * restrict nptr,
                    char ** restrict endptr);
               long double strtold(const char * restrict nptr,
                    char ** restrict endptr);
        Description

    2   The strtod, strtof, and strtold functions convert the initial portion of the string
        pointed to by nptr to double, float, and long double representation,
        respectively. First, they decompose the input string into three parts: an initial, possibly
        empty, sequence of white-space characters (as specified by the isspace function), a
        subject sequence resembling a floating-point constant or representing an infinity or NaN;
        and a final string of one or more unrecognized characters, including the terminating null
        character of the input string. Then, they attempt to convert the subject sequence to a
        floating-point number, and return the result.

    3   The expected form of the subject sequence is an optional plus or minus sign, then one of
        the following:
        — a nonempty sequence of decimal digits optionally containing a decimal-point
          character, then an optional exponent part as defined in 6.4.4.2;
        — a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
          decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
        — INF or INFINITY, ignoring case
        — NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
                   n-char-sequence:
                          digit
                          nondigit
                          n-char-sequence digit
                          n-char-sequence nondigit
        The subject sequence is defined as the longest initial subsequence of the input string,
        starting with the first non-white-space character, that is of the expected form. The subject
        sequence contains no characters if the input string is not of the expected form.

    4   If the subject sequence has the expected form for a floating-point number, the sequence of
        characters starting with the first digit or the decimal-point character (whichever occurs
        first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
        decimal-point character is used in place of a period, and that if neither an exponent part
        nor a decimal-point character appears in a decimal floating point number, or if a binary
        exponent part does not appear in a hexadecimal floating point number, an exponent part
        of the appropriate type with value zero is assumed to follow the last digit in the string. If
        the subject sequence begins with a minus sign, the sequence is interpreted as negated.[292]
        A character sequence INF or INFINITY is interpreted as an infinity, if representable in
        the return type, else like a floating constant that is too large for the range of the return
        type. A character sequence NAN or NAN(n-char-sequenceopt) is interpreted as a quiet
        NaN, if supported in the return type, else like a subject sequence part that does not have
        the expected form; the meaning of the n-char sequence is implementation-defined.[293] A
        pointer to the final string is stored in the object pointed to by endptr, provided that
        endptr is not a null pointer.

    Footnote 292) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
             negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
             methods may yield different results if rounding is toward positive or negative infinity. In either case,
             the functions honor the sign of zero if floating-point arithmetic supports signed zeros.

    Footnote 293) An implementation may use the n-char sequence to determine extra information to be represented in
             the NaN’s significand.

    5   If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
        value resulting from the conversion is correctly rounded.

    6   In other than the "C" locale, additional locale-specific subject sequence forms may be
        accepted.

    7   If the subject sequence is empty or does not have the expected form, no conversion is
        performed; the value of nptr is stored in the object pointed to by endptr, provided
        that endptr is not a null pointer.
        Recommended practice

    8   If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
        the result is not exactly representable, the result should be one of the two numbers in the
        appropriate internal format that are adjacent to the hexadecimal floating source value,
        with the extra stipulation that the error should have a correct sign for the current rounding
        direction.

    9   If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
        <float.h>) significant digits, the result should be correctly rounded. If the subject
        sequence D has the decimal form and more than DECIMAL_DIG significant digits,
        consider the two bounding, adjacent decimal strings L and U, both having
        DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L ≤ D ≤ U.
        The result should be one of the (equal or adjacent) values that would be obtained by
        correctly rounding L and U according to the current rounding direction, with the extra
         stipulation that the error with respect to D should have a correct sign for the current
         rounding direction.[294]
         Returns

    Footnote 294) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
              to the same internal floating value, but if not will round to adjacent values.

    10   The functions return the converted value, if any. If no conversion could be performed,
         zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
         plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
         return type and sign of the value), and the value of the macro ERANGE is stored in
         errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
         no greater than the smallest normalized positive number in the return type; whether
         errno acquires the value ERANGE is implementation-defined.

### 7.22.1.4 [The strtol, strtoll, strtoul, and strtoull functions]

    1 Synopsis
                #include <stdlib.h>
                 long int strtol(
                      const char * restrict nptr,
                      char ** restrict endptr,
                      int base);
                 long long int strtoll(
                      const char * restrict nptr,
                      char ** restrict endptr,
                      int base);
                 unsigned long int strtoul(
                      const char * restrict nptr,
                      char ** restrict endptr,
                      int base);
                 unsigned long long int strtoull(
                      const char * restrict nptr,
                      char ** restrict endptr,
                      int base);
         Description

    2    The strtol, strtoll, strtoul, and strtoull functions convert the initial
         portion of the string pointed to by nptr to long int, long long int, unsigned
         long int, and unsigned long long int representation, respectively. First,
         they decompose the input string into three parts: an initial, possibly empty, sequence of
         white-space characters (as specified by the isspace function), a subject sequence
        resembling an integer represented in some radix determined by the value of base, and a
        final string of one or more unrecognized characters, including the terminating null
        character of the input string. Then, they attempt to convert the subject sequence to an
        integer, and return the result.

    3   If the value of base is zero, the expected form of the subject sequence is that of an
        integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
        not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
        expected form of the subject sequence is a sequence of letters and digits representing an
        integer with the radix specified by base, optionally preceded by a plus or minus sign,
        but not including an integer suffix. The letters from a (or A) through z (or Z) are
        ascribed the values 10 through 35; only letters and digits whose ascribed values are less
        than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
        optionally precede the sequence of letters and digits, following the sign if present.

    4   The subject sequence is defined as the longest initial subsequence of the input string,
        starting with the first non-white-space character, that is of the expected form. The subject
        sequence contains no characters if the input string is empty or consists entirely of white
        space, or if the first non-white-space character is other than a sign or a permissible letter
        or digit.

    5   If the subject sequence has the expected form and the value of base is zero, the sequence
        of characters starting with the first digit is interpreted as an integer constant according to
        the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
        is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
        as given above. If the subject sequence begins with a minus sign, the value resulting from
        the conversion is negated (in the return type). A pointer to the final string is stored in the
        object pointed to by endptr, provided that endptr is not a null pointer.

    6   In other than the "C" locale, additional locale-specific subject sequence forms may be
        accepted.

    7   If the subject sequence is empty or does not have the expected form, no conversion is
        performed; the value of nptr is stored in the object pointed to by endptr, provided
        that endptr is not a null pointer.
        Returns

    8   The strtol, strtoll, strtoul, and strtoull functions return the converted
        value, if any. If no conversion could be performed, zero is returned. If the correct value
        is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
        LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
        and sign of the value, if any), and the value of the macro ERANGE is stored in errno.

### 7.22.2 [Pseudo-random sequence generation functions]

### 7.22.2.1 [The rand function]

    1 Synopsis
               #include <stdlib.h>
                int rand(void);
        Description

    2   The rand function computes a sequence of pseudo-random integers in the range 0 to
        RAND_MAX.[295]

    Footnote 295) There are no guarantees as to the quality of the random sequence produced and some implementations
             are known to produce sequences with distressingly non-random low-order bits. Applications with
             particular requirements should use a generator that is known to be sufficient for their needs.

    3   The rand function is not required to avoid data races with other calls to pseudo-random
        sequence generation functions. The implementation shall behave as if no library function
        calls the rand function.
        Returns

    4   The rand function returns a pseudo-random integer.
        Environmental limits

    5   The value of the RAND_MAX macro shall be at least 32767.

### 7.22.2.2 [The srand function]

    1 Synopsis
               #include <stdlib.h>
                void srand(unsigned int seed);
        Description

    2   The srand function uses the argument as a seed for a new sequence of pseudo-random
        numbers to be returned by subsequent calls to rand. If srand is then called with the
        same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
        called before any calls to srand have been made, the same sequence shall be generated
        as when srand is first called with a seed value of 1.

    3   The srand function is not required to avoid data races with other calls to pseudo-
        random sequence generation functions. The implementation shall behave as if no library
        function calls the srand function.
        Returns

    4   The srand function returns no value.

    5   EXAMPLE     The following functions define a portable implementation of rand and srand.
               static unsigned long int next = 1;
               int rand(void)   // RAND_MAX assumed to be 32767
               {
                     next = next * 1103515245 + 12345;
                     return (unsigned int)(next/65536) % 32768;
               }
               void srand(unsigned int seed)
               {
                     next = seed;
               }

### 7.22.3 [Memory management functions]

    1   The order and contiguity of storage allocated by successive calls to the
        aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
        pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
        a pointer to any type of object with a fundamental alignment requirement and then used
        to access such an object or an array of such objects in the space allocated (until the space
        is explicitly deallocated). The lifetime of an allocated object extends from the allocation
        until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
        any other object. The pointer returned points to the start (lowest byte address) of the
        allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
        the space requested is zero, the behavior is implementation-defined: either a null pointer
        is returned, or the behavior is as if the size were some nonzero value, except that the
        returned pointer shall not be used to access an object.

    2   For purposes of determining the existence of a data race, memory allocation functions
        behave as though they accessed only memory locations accessible through their
        arguments and not other static duration storage. These functions may, however, visibly
        modify the storage that they allocate or deallocate. A call to free or realloc that
        deallocates a region p of memory synchronizes with any allocation call that allocates all
        or part of the region p. This synchronization occurs after any access of p by the
        deallocating function, and before any such access by the allocating function.

### 7.22.3.1 [The aligned_alloc function]

    1 Synopsis
              #include <stdlib.h>
               void *aligned_alloc(size_t alignment, size_t size);
        Description

    2   The aligned_alloc function allocates space for an object whose alignment is
        specified by alignment, whose size is specified by size, and whose value is
        indeterminate. The value of alignment shall be a valid alignment supported by the
        implementation and the value of size shall be an integral multiple of alignment.
        Returns

    3   The aligned_alloc function returns either a null pointer or a pointer to the allocated
        space.

### 7.22.3.2 [The calloc function]

    1 Synopsis
               #include <stdlib.h>
                void *calloc(size_t nmemb, size_t size);
        Description

    2   The calloc function allocates space for an array of nmemb objects, each of whose size
        is size. The space is initialized to all bits zero.[296]
        Returns

    Footnote 296) Note that this need not be the same as the representation of floating-point zero or a null pointer
             constant.

    3   The calloc function returns either a null pointer or a pointer to the allocated space.

### 7.22.3.3 [The free function]

    1 Synopsis
               #include <stdlib.h>
                void free(void *ptr);
        Description

    2   The free function causes the space pointed to by ptr to be deallocated, that is, made
        available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
        the argument does not match a pointer earlier returned by a memory management
        function, or if the space has been deallocated by a call to free or realloc, the
        behavior is undefined.
        Returns

    3   The free function returns no value.

### 7.22.3.4 [The malloc function]

    1 Synopsis
              #include <stdlib.h>
               void *malloc(size_t size);
        Description

    2   The malloc function allocates space for an object whose size is specified by size and
        whose value is indeterminate.
        Returns

    3   The malloc function returns either a null pointer or a pointer to the allocated space.

### 7.22.3.5 [The realloc function]

    1 Synopsis
              #include <stdlib.h>
               void *realloc(void *ptr, size_t size);
        Description

    2   The realloc function deallocates the old object pointed to by ptr and returns a
        pointer to a new object that has the size specified by size. The contents of the new
        object shall be the same as that of the old object prior to deallocation, up to the lesser of
        the new and old sizes. Any bytes in the new object beyond the size of the old object have
        indeterminate values.

    3   If ptr is a null pointer, the realloc function behaves like the malloc function for the
        specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
        management function, or if the space has been deallocated by a call to the free or
        realloc function, the behavior is undefined. If memory for the new object cannot be
        allocated, the old object is not deallocated and its value is unchanged.
        Returns

    4   The realloc function returns a pointer to the new object (which may have the same
        value as a pointer to the old object), or a null pointer if the new object could not be
        allocated.

### 7.22.4 [Communication with the environment]

### 7.22.4.1 [The abort function]

    1 Synopsis
              #include <stdlib.h>
               _Noreturn void abort(void);
        Description

    2   The abort function causes abnormal program termination to occur, unless the signal
        SIGABRT is being caught and the signal handler does not return. Whether open streams
        with unwritten buffered data are flushed, open streams are closed, or temporary files are
        removed is implementation-defined. An implementation-defined form of the status
        unsuccessful termination is returned to the host environment by means of the function
        call raise(SIGABRT).
        Returns

    3   The abort function does not return to its caller.

### 7.22.4.2 [The atexit function]

    1 Synopsis
              #include <stdlib.h>
               int atexit(void (*func)(void));
        Description

    2   The atexit function registers the function pointed to by func, to be called without
        arguments at normal program termination.[297] It is unspecified whether a call to the
        atexit function that does not happen before the exit function is called will succeed.
        Environmental limits

    Footnote 297) The atexit function registrations are distinct from the at_quick_exit registrations, so
             applications may need to call both registration functions with the same argument.

    3   The implementation shall support the registration of at least 32 functions.
        Returns

    4   The atexit function returns zero if the registration succeeds, nonzero if it fails.
        Forward references: the at_quick_exit function (7.22.4.3), the exit function
        (7.22.4.4).

### 7.22.4.3 [The at_quick_exit function]

    1 Synopsis
               #include <stdlib.h>
                int at_quick_exit(void (*func)(void));
        Description

    2   The at_quick_exit function registers the function pointed to by func, to be called
        without arguments should quick_exit be called.[298] It is unspecified whether a call to
        the at_quick_exit function that does not happen before the quick_exit function
        is called will succeed.
        Environmental limits

    Footnote 298) The at_quick_exit function registrations are distinct from the atexit registrations, so
             applications may need to call both registration functions with the same argument.

    3   The implementation shall support the registration of at least 32 functions.
        Returns

    4   The at_quick_exit function returns zero if the registration succeeds, nonzero if it
        fails.
        Forward references: the quick_exit function (7.22.4.7).

### 7.22.4.4 [The exit function]

    1 Synopsis
               #include <stdlib.h>
                _Noreturn void exit(int status);
        Description

    2   The exit function causes normal program termination to occur. No functions registered
        by the at_quick_exit function are called. If a program calls the exit function
        more than once, or calls the quick_exit function in addition to the exit function, the
        behavior is undefined.

    3   First, all functions registered by the atexit function are called, in the reverse order of
        their registration,[299] except that a function is called after any previously registered
        functions that had already been called at the time it was registered. If, during the call to
        any such function, a call to the longjmp function is made that would terminate the call
        to the registered function, the behavior is undefined.

    Footnote 299) Each function is called as many times as it was registered, and in the correct order with respect to
             other registered functions.

    4   Next, all open streams with unwritten buffered data are flushed, all open streams are
        closed, and all files created by the tmpfile function are removed.

    5   Finally, control is returned to the host environment. If the value of status is zero or
        EXIT_SUCCESS, an implementation-defined form of the status successful termination is
        returned. If the value of status is EXIT_FAILURE, an implementation-defined form
        of the status unsuccessful termination is returned. Otherwise the status returned is
        implementation-defined.
        Returns

    6   The exit function cannot return to its caller.

### 7.22.4.5 [The _Exit function]

    1 Synopsis
               #include <stdlib.h>
                _Noreturn void _Exit(int status);
        Description

    2   The _Exit function causes normal program termination to occur and control to be
        returned to the host environment. No functions registered by the atexit function, the
        at_quick_exit function, or signal handlers registered by the signal function are
        called. The status returned to the host environment is determined in the same way as for
        the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
        flushed, open streams are closed, or temporary files are removed is implementation-
        defined.
        Returns

    3   The _Exit function cannot return to its caller.

### 7.22.4.6 [The getenv function]

    1 Synopsis
               #include <stdlib.h>
                char *getenv(const char *name);
        Description

    2   The getenv function searches an environment list, provided by the host environment,
        for a string that matches the string pointed to by name. The set of environment names
        and the method for altering the environment list are implementation-defined. The
        getenv function need not avoid data races with other threads of execution that modify
        the environment list.[300]

    Footnote 300) Many implementations provide non-standard functions that modify the environment list.

    3   The implementation shall behave as if no library function calls the getenv function.
        Returns

    4   The getenv function returns a pointer to a string associated with the matched list
        member. The string pointed to shall not be modified by the program, but may be
        overwritten by a subsequent call to the getenv function. If the specified name cannot
        be found, a null pointer is returned.

### 7.22.4.7 [The quick_exit function]

    1 Synopsis
               #include <stdlib.h>
                _Noreturn void quick_exit(int status);
        Description

    2   The quick_exit function causes normal program termination to occur. No functions
        registered by the atexit function or signal handlers registered by the signal function
        are called. If a program calls the quick_exit function more than once, or calls the
        exit function in addition to the quick_exit function, the behavior is undefined. If a
        signal is raised while the quick_exit function is executing, the behavior is undefined.

    3   The quick_exit function first calls all functions registered by the at_quick_exit
        function, in the reverse order of their registration,[301] except that a function is called after
        any previously registered functions that had already been called at the time it was
        registered. If, during the call to any such function, a call to the longjmp function is
        made that would terminate the call to the registered function, the behavior is undefined.

    Footnote 301) Each function is called as many times as it was registered, and in the correct order with respect to
             other registered functions.

    4   Then control is returned to the host environment by means of the function call
        _Exit(status).
        Returns

    5   The quick_exit function cannot return to its caller.

### 7.22.4.8 [The system function]

    1 Synopsis
               #include <stdlib.h>
                int system(const char *string);
        Description

    2   If string is a null pointer, the system function determines whether the host
        environment has a command processor. If string is not a null pointer, the system
        function passes the string pointed to by string to that command processor to be
        executed in a manner which the implementation shall document; this might then cause the
        program calling system to behave in a non-conforming manner or to terminate.
        Returns

    3   If the argument is a null pointer, the system function returns nonzero only if a
        command processor is available. If the argument is not a null pointer, and the system
        function does return, it returns an implementation-defined value.

### 7.22.5 [Searching and sorting utilities]

    1   These utilities make use of a comparison function to search or sort arrays of unspecified
        type. Where an argument declared as size_t nmemb specifies the length of the array
        for a function, nmemb can have the value zero on a call to that function; the comparison
        function is not called, a search finds no matching element, and sorting performs no
        rearrangement. Pointer arguments on such a call shall still have valid values, as described
        in 7.1.4.

    2   The implementation shall ensure that the second argument of the comparison function
        (when called from bsearch), or both arguments (when called from qsort), are
        pointers to elements of the array.[302] The first argument when called from bsearch
        shall equal key.

    Footnote 302) That is, if the value passed is p, then the following expressions are always nonzero:
                      ((char *)p - (char *)base) % size == 0
                      (char *)p >= (char *)base
                      (char *)p < (char *)base + nmemb * size

    3   The comparison function shall not alter the contents of the array. The implementation
        may reorder elements of the array between calls to the comparison function, but shall not
        alter the contents of any individual element.

    4   When the same objects (consisting of size bytes, irrespective of their current positions
        in the array) are passed more than once to the comparison function, the results shall be
        consistent with one another. That is, for qsort they shall define a total ordering on the
        array, and for bsearch the same object shall always compare the same way with the
        key.

    5   A sequence point occurs immediately before and immediately after each call to the
        comparison function, and also between any call to the comparison function and any
        movement of the objects passed as arguments to that call.

### 7.22.5.1 [The bsearch function]

    1 Synopsis
                #include <stdlib.h>
                 void *bsearch(const void *key, const void *base,
                      size_t nmemb, size_t size,
                      int (*compar)(const void *, const void *));
        Description

    2   The bsearch function searches an array of nmemb objects, the initial element of which
        is pointed to by base, for an element that matches the object pointed to by key. The
        size of each element of the array is specified by size.

    3   The comparison function pointed to by compar is called with two arguments that point
        to the key object and to an array element, in that order. The function shall return an
        integer less than, equal to, or greater than zero if the key object is considered,
        respectively, to be less than, to match, or to be greater than the array element. The array
        shall consist of: all the elements that compare less than, all the elements that compare
        equal to, and all the elements that compare greater than the key object, in that order.[303]
        Returns

    Footnote 303) In practice, the entire array is sorted according to the comparison function.

    4   The bsearch function returns a pointer to a matching element of the array, or a null
        pointer if no match is found. If two elements compare as equal, which element is
        matched is unspecified.

### 7.22.5.2 [The qsort function]

    1 Synopsis
                #include <stdlib.h>
                 void qsort(void *base, size_t nmemb, size_t size,
                      int (*compar)(const void *, const void *));
        Description

    2   The qsort function sorts an array of nmemb objects, the initial element of which is
        pointed to by base. The size of each object is specified by size.

    3   The contents of the array are sorted into ascending order according to a comparison
        function pointed to by compar, which is called with two arguments that point to the
        objects being compared. The function shall return an integer less than, equal to, or
        greater than zero if the first argument is considered to be respectively less than, equal to,
        or greater than the second.

    4   If two elements compare as equal, their order in the resulting sorted array is unspecified.
        Returns

    5   The qsort function returns no value.

### 7.22.6 [Integer arithmetic functions]

### 7.22.6.1 [The abs, labs and llabs functions]

    1 Synopsis
               #include <stdlib.h>
                int abs(int j);
                long int labs(long int j);
                long long int llabs(long long int j);
        Description

    2   The abs, labs, and llabs functions compute the absolute value of an integer j. If the
        result cannot be represented, the behavior is undefined.[304]
        Returns

    Footnote 304) The absolute value of the most negative number cannot be represented in two’s complement.

    3   The abs, labs, and llabs, functions return the absolute value.

### 7.22.6.2 [The div, ldiv, and lldiv functions]

    1 Synopsis
               #include <stdlib.h>
                div_t div(int numer, int denom);
                ldiv_t ldiv(long int numer, long int denom);
                lldiv_t lldiv(long long int numer, long long int denom);
        Description

    2   The div, ldiv, and lldiv, functions compute numer / denom and numer %
        denom in a single operation.
        Returns

    3   The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
        lldiv_t, respectively, comprising both the quotient and the remainder. The structures
        shall contain (in either order) the members quot (the quotient) and rem (the remainder),
        each of which has the same type as the arguments numer and denom. If either part of
        the result cannot be represented, the behavior is undefined.

### 7.22.7 [Multibyte/wide character conversion functions]

    1   The behavior of the multibyte character functions is affected by the LC_CTYPE category
        of the current locale. For a state-dependent encoding, each function is placed into its
        initial conversion state at program startup and can be returned to that state by a call for
        which its character pointer argument, s, is a null pointer. Subsequent calls with s as
        other than a null pointer cause the internal conversion state of the function to be altered as
        necessary. A call with s as a null pointer causes these functions to return a nonzero value
        if encodings have state dependency, and zero otherwise.[305] Changing the LC_CTYPE
        category causes the conversion state of these functions to be indeterminate.

    Footnote 305) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
             character codes, but are grouped with an adjacent multibyte character.

### 7.22.7.1 [The mblen function]

    1 Synopsis
               #include <stdlib.h>
                int mblen(const char *s, size_t n);
        Description

    2   If s is not a null pointer, the mblen function determines the number of bytes contained
        in the multibyte character pointed to by s. Except that the conversion state of the
        mbtowc function is not affected, it is equivalent to
                mbtowc((wchar_t *)0, (const char *)0, 0);
                mbtowc((wchar_t *)0, s, n);

    3   The implementation shall behave as if no library function calls the mblen function.
        Returns

    4   If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
        character encodings, respectively, do or do not have state-dependent encodings. If s is
        not a null pointer, the mblen function either returns 0 (if s points to the null character),
        or returns the number of bytes that are contained in the multibyte character (if the next n
        or fewer bytes form a valid multibyte character), or returns −1 (if they do not form a valid
        multibyte character).
        Forward references: the mbtowc function (7.22.7.2).

### 7.22.7.2 [The mbtowc function]

    1 Synopsis
              #include <stdlib.h>
               int mbtowc(wchar_t * restrict pwc,
                    const char * restrict s,
                    size_t n);
        Description

    2   If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
        the byte pointed to by s to determine the number of bytes needed to complete the next
        multibyte character (including any shift sequences). If the function determines that the
        next multibyte character is complete and valid, it determines the value of the
        corresponding wide character and then, if pwc is not a null pointer, stores that value in
        the object pointed to by pwc. If the corresponding wide character is the null wide
        character, the function is left in the initial conversion state.

    3   The implementation shall behave as if no library function calls the mbtowc function.
        Returns

    4   If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
        character encodings, respectively, do or do not have state-dependent encodings. If s is
        not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
        or returns the number of bytes that are contained in the converted multibyte character (if
        the next n or fewer bytes form a valid multibyte character), or returns −1 (if they do not
        form a valid multibyte character).

    5   In no case will the value returned be greater than n or the value of the MB_CUR_MAX
        macro.

### 7.22.7.3 [The wctomb function]

    1 Synopsis
              #include <stdlib.h>
               int wctomb(char *s, wchar_t wc);
        Description

    2   The wctomb function determines the number of bytes needed to represent the multibyte
        character corresponding to the wide character given by wc (including any shift
        sequences), and stores the multibyte character representation in the array whose first
        element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
        are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
        sequence needed to restore the initial shift state, and the function is left in the initial
        conversion state.

    3   The implementation shall behave as if no library function calls the wctomb function.
        Returns

    4   If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
        character encodings, respectively, do or do not have state-dependent encodings. If s is
        not a null pointer, the wctomb function returns −1 if the value of wc does not correspond
        to a valid multibyte character, or returns the number of bytes that are contained in the
        multibyte character corresponding to the value of wc.

    5   In no case will the value returned be greater than the value of the MB_CUR_MAX macro.

### 7.22.8 [Multibyte/wide string conversion functions]

    1   The behavior of the multibyte string functions is affected by the LC_CTYPE category of
        the current locale.

### 7.22.8.1 [The mbstowcs function]

    1 Synopsis
                #include <stdlib.h>
                 size_t mbstowcs(wchar_t * restrict pwcs,
                      const char * restrict s,
                      size_t n);
        Description

    2   The mbstowcs function converts a sequence of multibyte characters that begins in the
        initial shift state from the array pointed to by s into a sequence of corresponding wide
        characters and stores not more than n wide characters into the array pointed to by pwcs.
        No multibyte characters that follow a null character (which is converted into a null wide
        character) will be examined or converted. Each multibyte character is converted as if by
        a call to the mbtowc function, except that the conversion state of the mbtowc function is
        not affected.

    3   No more than n elements will be modified in the array pointed to by pwcs. If copying
        takes place between objects that overlap, the behavior is undefined.
        Returns

    4   If an invalid multibyte character is encountered, the mbstowcs function returns
        (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
        elements modified, not including a terminating null wide character, if any.[306]

    Footnote 306) The array will not be null-terminated if the value returned is n.

### 7.22.8.2 [The wcstombs function]

    1 Synopsis
              #include <stdlib.h>
               size_t wcstombs(char * restrict s,
                    const wchar_t * restrict pwcs,
                    size_t n);
        Description

    2   The wcstombs function converts a sequence of wide characters from the array pointed
        to by pwcs into a sequence of corresponding multibyte characters that begins in the
        initial shift state, and stores these multibyte characters into the array pointed to by s,
        stopping if a multibyte character would exceed the limit of n total bytes or if a null
        character is stored. Each wide character is converted as if by a call to the wctomb
        function, except that the conversion state of the wctomb function is not affected.

    3   No more than n bytes will be modified in the array pointed to by s. If copying takes place
        between objects that overlap, the behavior is undefined.
        Returns

    4   If a wide character is encountered that does not correspond to a valid multibyte character,
        the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
        returns the number of bytes modified, not including a terminating null character, if
        any.[306]

    Footnote 306) The array will not be null-terminated if the value returned is n.

### 7.23 [_Noreturn <stdnoreturn.h>]

    1   The header <stdnoreturn.h> defines the macro
              noreturn
        which expands to _Noreturn.

### 7.24 [String handling <string.h>]

### 7.24.1 [String function conventions]

    1   The header <string.h> declares one type and several functions, and defines one
        macro useful for manipulating arrays of character type and other objects treated as arrays
        of character type.[307] The type is size_t and the macro is NULL (both described in
        7.19). Various methods are used for determining the lengths of the arrays, but in all cases
        a char * or void * argument points to the initial (lowest addressed) character of the
        array. If an array is accessed beyond the end of an object, the behavior is undefined.

    Footnote 307) See ‘‘future library directions’’ (7.31.13).

    2   Where an argument declared as size_t n specifies the length of the array for a
        function, n can have the value zero on a call to that function. Unless explicitly stated
        otherwise in the description of a particular function in this subclause, pointer arguments
        on such a call shall still have valid values, as described in 7.1.4. On such a call, a
        function that locates a character finds no occurrence, a function that compares two
        character sequences returns zero, and a function that copies characters copies zero
        characters.

    3   For all functions in this subclause, each character shall be interpreted as if it had the type
        unsigned char (and therefore every possible object representation is valid and has a
        different value).

### 7.24.2 [Copying functions]

### 7.24.2.1 [The memcpy function]

    1 Synopsis
                #include <string.h>
                 void *memcpy(void * restrict s1,
                      const void * restrict s2,
                      size_t n);
        Description

    2   The memcpy function copies n characters from the object pointed to by s2 into the
        object pointed to by s1. If copying takes place between objects that overlap, the behavior
        is undefined.
        Returns

    3   The memcpy function returns the value of s1.

### 7.24.2.2 [The memmove function]

    1 Synopsis
              #include <string.h>
               void *memmove(void *s1, const void *s2, size_t n);
        Description

    2   The memmove function copies n characters from the object pointed to by s2 into the
        object pointed to by s1. Copying takes place as if the n characters from the object
        pointed to by s2 are first copied into a temporary array of n characters that does not
        overlap the objects pointed to by s1 and s2, and then the n characters from the
        temporary array are copied into the object pointed to by s1.
        Returns

    3   The memmove function returns the value of s1.

### 7.24.2.3 [The strcpy function]

    1 Synopsis
              #include <string.h>
               char *strcpy(char * restrict s1,
                    const char * restrict s2);
        Description

    2   The strcpy function copies the string pointed to by s2 (including the terminating null
        character) into the array pointed to by s1. If copying takes place between objects that
        overlap, the behavior is undefined.
        Returns

    3   The strcpy function returns the value of s1.

### 7.24.2.4 [The strncpy function]

    1 Synopsis
              #include <string.h>
               char *strncpy(char * restrict s1,
                    const char * restrict s2,
                    size_t n);
        Description

    2   The strncpy function copies not more than n characters (characters that follow a null
        character are not copied) from the array pointed to by s2 to the array pointed to by
        s1.[308] If copying takes place between objects that overlap, the behavior is undefined.

    Footnote 308) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
             not be null-terminated.

    3   If the array pointed to by s2 is a string that is shorter than n characters, null characters
        are appended to the copy in the array pointed to by s1, until n characters in all have been
        written.
        Returns

    4   The strncpy function returns the value of s1.

### 7.24.3 [Concatenation functions]

### 7.24.3.1 [The strcat function]

    1 Synopsis
                #include <string.h>
                 char *strcat(char * restrict s1,
                      const char * restrict s2);
        Description

    2   The strcat function appends a copy of the string pointed to by s2 (including the
        terminating null character) to the end of the string pointed to by s1. The initial character
        of s2 overwrites the null character at the end of s1. If copying takes place between
        objects that overlap, the behavior is undefined.
        Returns

    3   The strcat function returns the value of s1.

### 7.24.3.2 [The strncat function]

    1 Synopsis
                #include <string.h>
                 char *strncat(char * restrict s1,
                      const char * restrict s2,
                      size_t n);
        Description

    2   The strncat function appends not more than n characters (a null character and
        characters that follow it are not appended) from the array pointed to by s2 to the end of
        the string pointed to by s1. The initial character of s2 overwrites the null character at the
        end of s1. A terminating null character is always appended to the result.[309] If copying
        takes place between objects that overlap, the behavior is undefined.
        Returns

    Footnote 309) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
             strlen(s1)+n+1.

    3   The strncat function returns the value of s1.
        Forward references: the strlen function (7.24.6.3).

### 7.24.4 [Comparison functions]

    1   The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
        and strncmp is determined by the sign of the difference between the values of the first
        pair of characters (both interpreted as unsigned char) that differ in the objects being
        compared.

### 7.24.4.1 [The memcmp function]

    1 Synopsis
               #include <string.h>
                int memcmp(const void *s1, const void *s2, size_t n);
        Description

    2   The memcmp function compares the first n characters of the object pointed to by s1 to
        the first n characters of the object pointed to by s2.[310]
        Returns

    Footnote 310) The contents of ‘‘holes’’ used as padding for purposes of alignment within structure objects are
             indeterminate. Strings shorter than their allocated space and unions may also cause problems in
             comparison.

    3   The memcmp function returns an integer greater than, equal to, or less than zero,
        accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
        pointed to by s2.

### 7.24.4.2 [The strcmp function]

    1 Synopsis
               #include <string.h>
                int strcmp(const char *s1, const char *s2);
        Description

    2   The strcmp function compares the string pointed to by s1 to the string pointed to by
        s2.
        Returns

    3   The strcmp function returns an integer greater than, equal to, or less than zero,
        accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
        pointed to by s2.

### 7.24.4.3 [The strcoll function]

    1 Synopsis
              #include <string.h>
               int strcoll(const char *s1, const char *s2);
        Description

    2   The strcoll function compares the string pointed to by s1 to the string pointed to by
        s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
        Returns

    3   The strcoll function returns an integer greater than, equal to, or less than zero,
        accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
        pointed to by s2 when both are interpreted as appropriate to the current locale.

### 7.24.4.4 [The strncmp function]

    1 Synopsis
              #include <string.h>
               int strncmp(const char *s1, const char *s2, size_t n);
        Description

    2   The strncmp function compares not more than n characters (characters that follow a
        null character are not compared) from the array pointed to by s1 to the array pointed to
        by s2.
        Returns

    3   The strncmp function returns an integer greater than, equal to, or less than zero,
        accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
        to, or less than the possibly null-terminated array pointed to by s2.

### 7.24.4.5 [The strxfrm function]

    1 Synopsis
              #include <string.h>
               size_t strxfrm(char * restrict s1,
                    const char * restrict s2,
                    size_t n);
        Description

    2   The strxfrm function transforms the string pointed to by s2 and places the resulting
        string into the array pointed to by s1. The transformation is such that if the strcmp
        function is applied to two transformed strings, it returns a value greater than, equal to, or
        less than zero, corresponding to the result of the strcoll function applied to the same
        two original strings. No more than n characters are placed into the resulting array
        pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
        be a null pointer. If copying takes place between objects that overlap, the behavior is
        undefined.
        Returns

    3   The strxfrm function returns the length of the transformed string (not including the
        terminating null character). If the value returned is n or more, the contents of the array
        pointed to by s1 are indeterminate.

    4   EXAMPLE The value of the following expression is the size of the array needed to hold the
        transformation of the string pointed to by s.
               1 + strxfrm(NULL, s, 0)

### 7.24.5 [Search functions]

### 7.24.5.1 [The memchr function]

    1 Synopsis
              #include <string.h>
               void *memchr(const void *s, int c, size_t n);
        Description

    2   The memchr function locates the first occurrence of c (converted to an unsigned
        char) in the initial n characters (each interpreted as unsigned char) of the object
        pointed to by s. The implementation shall behave as if it reads the characters sequentially
        and stops as soon as a matching character is found.
        Returns

    3   The memchr function returns a pointer to the located character, or a null pointer if the
        character does not occur in the object.

### 7.24.5.2 [The strchr function]

    1 Synopsis
              #include <string.h>
               char *strchr(const char *s, int c);
        Description

    2   The strchr function locates the first occurrence of c (converted to a char) in the
        string pointed to by s. The terminating null character is considered to be part of the
        string.
        Returns

    3   The strchr function returns a pointer to the located character, or a null pointer if the
        character does not occur in the string.

### 7.24.5.3 [The strcspn function]

    1 Synopsis
              #include <string.h>
               size_t strcspn(const char *s1, const char *s2);
        Description

    2   The strcspn function computes the length of the maximum initial segment of the string
        pointed to by s1 which consists entirely of characters not from the string pointed to by
        s2.
        Returns

    3   The strcspn function returns the length of the segment.

### 7.24.5.4 [The strpbrk function]

    1 Synopsis
              #include <string.h>
               char *strpbrk(const char *s1, const char *s2);
        Description

    2   The strpbrk function locates the first occurrence in the string pointed to by s1 of any
        character from the string pointed to by s2.
        Returns

    3   The strpbrk function returns a pointer to the character, or a null pointer if no character
        from s2 occurs in s1.

### 7.24.5.5 [The strrchr function]

    1 Synopsis
              #include <string.h>
               char *strrchr(const char *s, int c);
        Description

    2   The strrchr function locates the last occurrence of c (converted to a char) in the
        string pointed to by s. The terminating null character is considered to be part of the
        string.
        Returns

    3   The strrchr function returns a pointer to the character, or a null pointer if c does not
        occur in the string.

### 7.24.5.6 [The strspn function]

    1 Synopsis
              #include <string.h>
               size_t strspn(const char *s1, const char *s2);
        Description

    2   The strspn function computes the length of the maximum initial segment of the string
        pointed to by s1 which consists entirely of characters from the string pointed to by s2.
        Returns

    3   The strspn function returns the length of the segment.

### 7.24.5.7 [The strstr function]

    1 Synopsis
              #include <string.h>
               char *strstr(const char *s1, const char *s2);
        Description

    2   The strstr function locates the first occurrence in the string pointed to by s1 of the
        sequence of characters (excluding the terminating null character) in the string pointed to
        by s2.
        Returns

    3   The strstr function returns a pointer to the located string, or a null pointer if the string
        is not found. If s2 points to a string with zero length, the function returns s1.

### 7.24.5.8 [The strtok function]

    1 Synopsis
              #include <string.h>
               char *strtok(char * restrict s1,
                    const char * restrict s2);
        Description

    2   A sequence of calls to the strtok function breaks the string pointed to by s1 into a
        sequence of tokens, each of which is delimited by a character from the string pointed to
        by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
        sequence have a null first argument. The separator string pointed to by s2 may be
        different from call to call.

    3   The first call in the sequence searches the string pointed to by s1 for the first character
        that is not contained in the current separator string pointed to by s2. If no such character
        is found, then there are no tokens in the string pointed to by s1 and the strtok function
        returns a null pointer. If such a character is found, it is the start of the first token.

    4   The strtok function then searches from there for a character that is contained in the
        current separator string. If no such character is found, the current token extends to the
        end of the string pointed to by s1, and subsequent searches for a token will return a null
        pointer. If such a character is found, it is overwritten by a null character, which
        terminates the current token. The strtok function saves a pointer to the following
        character, from which the next search for a token will start.

    5   Each subsequent call, with a null pointer as the value of the first argument, starts
        searching from the saved pointer and behaves as described above.

    6   The strtok function is not required to avoid data races with other calls to the strtok
        function.[311] The implementation shall behave as if no library function calls the strtok
        function.
        Returns

    Footnote 311) The strtok_s function can be used instead to avoid data races.

    7   The strtok function returns a pointer to the first character of a token, or a null pointer
        if there is no token.

    8   EXAMPLE
                #include <string.h>
                static char str[] = "?a???b,,,#c";
                char *t;
                t = strtok(str, "?");   // t points to the token "a"
                t = strtok(NULL, ","); // t points to the token "??b"
                t = strtok(NULL, "#,"); // t points to the token "c"
                t = strtok(NULL, "?"); // t is a null pointer

        Forward references: The strtok_s function (K.3.7.3.1).

### 7.24.6 [Miscellaneous functions]

### 7.24.6.1 [The memset function]

    1 Synopsis
               #include <string.h>
                void *memset(void *s, int c, size_t n);
        Description

    2   The memset function copies the value of c (converted to an unsigned char) into
        each of the first n characters of the object pointed to by s.
        Returns

    3   The memset function returns the value of s.

### 7.24.6.2 [The strerror function]

    1 Synopsis
               #include <string.h>
                char *strerror(int errnum);
        Description

    2   The strerror function maps the number in errnum to a message string. Typically,
        the values for errnum come from errno, but strerror shall map any value of type
        int to a message.

    3   The strerror function is not required to avoid data races with other calls to the
        strerror function.[312] The implementation shall behave as if no library function calls
        the strerror function.
        Returns

    Footnote 312) The strerror_s function can be used instead to avoid data races.

    4   The strerror function returns a pointer to the string, the contents of which are locale-
        specific. The array pointed to shall not be modified by the program, but may be
        overwritten by a subsequent call to the strerror function.
        Forward references: The strerror_s function (K.3.7.4.2).

### 7.24.6.3 [The strlen function]

    1 Synopsis
              #include <string.h>
               size_t strlen(const char *s);
        Description

    2   The strlen function computes the length of the string pointed to by s.
        Returns

    3   The strlen function returns the number of characters that precede the terminating null
        character.

### 7.25 [Type-generic math <tgmath.h>]

    1   The header <tgmath.h> includes the headers <math.h> and <complex.h> and
        defines several type-generic macros.

    2   Of the <math.h> and <complex.h> functions without an f (float) or l (long
        double) suffix, several have one or more parameters whose corresponding real type is
        double. For each such function, except modf, there is a corresponding type-generic
        macro.[313] The parameters whose corresponding real type is double in the function
        synopsis are generic parameters. Use of the macro invokes a function whose
        corresponding real type and type domain are determined by the arguments for the generic
        parameters.[314]

    Footnote 313) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
             make available the corresponding ordinary function.

    Footnote 314) If the type of the argument is not compatible with the type of the parameter for the selected function,
             the behavior is undefined.

    3   Use of the macro invokes a function whose generic parameters have the corresponding
        real type determined as follows:
        — First, if any argument for generic parameters has type long double, the type
          determined is long double.
        — Otherwise, if any argument for generic parameters has type double or is of integer
          type, the type determined is double.
        — Otherwise, the type determined is float.

    4   For each unsuffixed function in <math.h> for which there is a function in
        <complex.h> with the same name except for a c prefix, the corresponding type-
        generic macro (for both functions) has the same name as the function in <math.h>. The
        corresponding type-generic macro for fabs and cabs is fabs.
                <math.h>          <complex.h>           type-generic
                 function            function              macro
                 acos               cacos                 acos
                 asin               casin                 asin
                 atan               catan                 atan
                 acosh              cacosh                acosh
                 asinh              casinh                asinh
                 atanh              catanh                atanh
                 cos                ccos                  cos
                 sin                csin                  sin
                 tan                ctan                  tan
                 cosh               ccosh                 cosh
                 sinh               csinh                 sinh
                 tanh               ctanh                 tanh
                 exp                cexp                  exp
                 log                clog                  log
                 pow                cpow                  pow
                 sqrt               csqrt                 sqrt
                 fabs               cabs                  fabs
        If at least one argument for a generic parameter is complex, then use of the macro invokes
        a complex function; otherwise, use of the macro invokes a real function.

    5   For each unsuffixed function in <math.h> without a c-prefixed counterpart in
        <complex.h> (except modf), the corresponding type-generic macro has the same
        name as the function. These type-generic macros are:
              atan2                fma                  llround              remainder
              cbrt                 fmax                 log10                remquo
              ceil                 fmin                 log1p                rint
              copysign             fmod                 log2                 round
              erf                  frexp                logb                 scalbn
              erfc                 hypot                lrint                scalbln
              exp2                 ilogb                lround               tgamma
              expm1                ldexp                nearbyint            trunc
              fdim                 lgamma               nextafter
              floor                llrint               nexttoward
        If all arguments for generic parameters are real, then use of the macro invokes a real
        function; otherwise, use of the macro results in undefined behavior.

    6   For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a
        function in <math.h>, the corresponding type-generic macro has the same name as the
        function. These type-generic macros are:
               carg                     conj                     creal
               cimag                    cproj
        Use of the macro with any real or complex argument invokes a complex function.

    7   EXAMPLE       With the declarations
                #include <tgmath.h>
                int n;
                float f;
                double d;
                long double ld;
                float complex fc;
                double complex dc;
                long double complex ldc;
        functions invoked by use of type-generic macros are shown in the following table:
                         macro use                                   invokes
                    exp(n)                              exp(n), the function
                    acosh(f)                            acoshf(f)
                    sin(d)                              sin(d), the function
                    atan(ld)                            atanl(ld)
                    log(fc)                             clogf(fc)
                    sqrt(dc)                            csqrt(dc)
                    pow(ldc, f)                         cpowl(ldc, f)
                    remainder(n, n)                     remainder(n, n), the function
                    nextafter(d, f)                     nextafter(d, f), the function
                    nexttoward(f, ld)                   nexttowardf(f, ld)
                    copysign(n, ld)                     copysignl(n, ld)
                    ceil(fc)                            undefined behavior
                    rint(dc)                            undefined behavior
                    fmax(ldc, ld)                       undefined behavior
                    carg(n)                             carg(n), the function
                    cproj(f)                            cprojf(f)
                    creal(d)                            creal(d), the function
                    cimag(ld)                           cimagl(ld)
                    fabs(fc)                            cabsf(fc)
                    carg(dc)                            carg(dc), the function
                    cproj(ldc)                          cprojl(ldc)

### 7.26 [Threads <threads.h>]

### 7.26.1 [Introduction]

    1   The header <threads.h> includes the header <time.h>, defines macros, and
        declares types, enumeration constants, and functions that support multiple threads of
        execution.[315]

    Footnote 315) See ‘‘future library directions’’ (7.31.15).

    2   Implementations that define the macro _ _STDC_NO_THREADS_ _ need not provide
        this header nor support any of its facilities.

    3   The macros are
                 thread_local
        which expands to _Thread_local;
                 ONCE_FLAG_INIT
        which expands to a value that can be used to initialize an object of type once_flag;
        and
                 TSS_DTOR_ITERATIONS
        which expands to an integer constant expression representing the maximum number of
        times that destructors will be called when a thread terminates.

    4   The types are
                 cnd_t
        which is a complete object type that holds an identifier for a condition variable;
                 thrd_t
        which is a complete object type that holds an identifier for a thread;
                 tss_t
        which is a complete object type that holds an identifier for a thread-specific storage
        pointer;
                 mtx_t
        which is a complete object type that holds an identifier for a mutex;
                 tss_dtor_t
        which is the function pointer type void (*)(void*), used for a destructor for a
        thread-specific storage pointer;
               thrd_start_t
        which is the function pointer type int (*)(void*) that is passed to thrd_create
        to create a new thread; and
               once_flag
        which is a complete object type that holds a flag for use by call_once.

    5   The enumeration constants are
               mtx_plain
        which is passed to mtx_init to create a mutex object that supports neither timeout nor
        test and return;
               mtx_recursive
        which is passed to mtx_init to create a mutex object that supports recursive locking;
               mtx_timed
        which is passed to mtx_init to create a mutex object that supports timeout;
               thrd_timedout
        which is returned by a timed wait function to indicate that the time specified in the call
        was reached without acquiring the requested resource;
               thrd_success
        which is returned by a function to indicate that the requested operation succeeded;
               thrd_busy
        which is returned by a function to indicate that the requested operation failed because a
        resource requested by a test and return function is already in use;
               thrd_error
        which is returned by a function to indicate that the requested operation failed; and
               thrd_nomem
        which is returned by a function to indicate that the requested operation failed because it
        was unable to allocate memory.
        Forward references: date and time (7.27).

### 7.26.2 [Initialization functions]

### 7.26.2.1 [The call_once function]

    1 Synopsis
              #include <threads.h>
               void call_once(once_flag *flag, void (*func)(void));
        Description

    2   The call_once function uses the once_flag pointed to by flag to ensure that
        func is called exactly once, the first time the call_once function is called with that
        value of flag. Completion of an effective call to the call_once function synchronizes
        with all subsequent calls to the call_once function with the same value of flag.
        Returns

    3   The call_once function returns no value.

### 7.26.3 [Condition variable functions]

### 7.26.3.1 [The cnd_broadcast function]

    1 Synopsis
              #include <threads.h>
               int cnd_broadcast(cnd_t *cond);
        Description

    2   The cnd_broadcast function unblocks all of the threads that are blocked on the
        condition variable pointed to by cond at the time of the call. If no threads are blocked
        on the condition variable pointed to by cond at the time of the call, the function does
        nothing.
        Returns

    3   The cnd_broadcast function returns thrd_success on success, or thrd_error
        if the request could not be honored.

### 7.26.3.2 [The cnd_destroy function]

    1 Synopsis
              #include <threads.h>
               void cnd_destroy(cnd_t *cond);
        Description

    2   The cnd_destroy function releases all resources used by the condition variable
        pointed to by cond. The cnd_destroy function requires that no threads be blocked
        waiting for the condition variable pointed to by cond.
        Returns

    3   The cnd_destroy function returns no value.

### 7.26.3.3 [The cnd_init function]

    1 Synopsis
              #include <threads.h>
               int cnd_init(cnd_t *cond);
        Description

    2   The cnd_init function creates a condition variable. If it succeeds it sets the variable
        pointed to by cond to a value that uniquely identifies the newly created condition
        variable. A thread that calls cnd_wait on a newly created condition variable will
        block.
        Returns

    3   The cnd_init function returns thrd_success on success, or thrd_nomem if no
        memory could be allocated for the newly created condition, or thrd_error if the
        request could not be honored.

### 7.26.3.4 [The cnd_signal function]

    1 Synopsis
              #include <threads.h>
               int cnd_signal(cnd_t *cond);
        Description

    2   The cnd_signal function unblocks one of the threads that are blocked on the
        condition variable pointed to by cond at the time of the call. If no threads are blocked
        on the condition variable at the time of the call, the function does nothing and return
        success.
        Returns

    3   The cnd_signal function returns thrd_success on success or thrd_error if
        the request could not be honored.

### 7.26.3.5 [The cnd_timedwait function]

    1 Synopsis
              #include <threads.h>
               int cnd_timedwait(cnd_t *restrict cond,
                    mtx_t *restrict mtx,
                    const struct timespec *restrict ts);
        Description

    2   The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
        endeavors to block until the condition variable pointed to by cond is signaled by a call to
        cnd_signal or to cnd_broadcast, or until after the TIME_UTC-based calendar
        time pointed to by ts. When the calling thread becomes unblocked it locks the variable
        pointed to by mtx before it returns. The cnd_timedwait function requires that the
        mutex pointed to by mtx be locked by the calling thread.
        Returns

    3   The cnd_timedwait function returns thrd_success upon success, or
        thrd_timedout if the time specified in the call was reached without acquiring the
        requested resource, or thrd_error if the request could not be honored.

### 7.26.3.6 [The cnd_wait function]

    1 Synopsis
              #include <threads.h>
               int cnd_wait(cnd_t *cond, mtx_t *mtx);
        Description

    2   The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
        to block until the condition variable pointed to by cond is signaled by a call to
        cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
        locks the mutex pointed to by mtx before it returns. The cnd_wait function requires
        that the mutex pointed to by mtx be locked by the calling thread.
        Returns

    3   The cnd_wait function returns thrd_success on success or thrd_error if the
        request could not be honored.

### 7.26.4 [Mutex functions]

### 7.26.4.1 [The mtx_destroy function]

    1 Synopsis
              #include <threads.h>
               void mtx_destroy(mtx_t *mtx);
        Description

    2   The mtx_destroy function releases any resources used by the mutex pointed to by
        mtx. No threads can be blocked waiting for the mutex pointed to by mtx.
        Returns

    3   The mtx_destroy function returns no value.

### 7.26.4.2 [The mtx_init function]

    1 Synopsis
              #include <threads.h>
               int mtx_init(mtx_t *mtx, int type);
        Description

    2   The mtx_init function creates a mutex object with properties indicated by type,
        which must have one of the six values:
        mtx_plain for a simple non-recursive mutex,
        mtx_timed for a non-recursive mutex that supports timeout,                      ∗
        mtx_plain | mtx_recursive for a simple recursive mutex, or
        mtx_timed | mtx_recursive for a recursive mutex that supports timeout.

    3   If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
        uniquely identifies the newly created mutex.
        Returns

    4   The mtx_init function returns thrd_success on success, or thrd_error if the
        request could not be honored.

### 7.26.4.3 [The mtx_lock function]

    1 Synopsis
              #include <threads.h>
               int mtx_lock(mtx_t *mtx);
        Description

    2   The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
        is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
        on the same mutex shall synchronize with this operation.
        Returns

    3   The mtx_lock function returns thrd_success on success, or thrd_error if the ∗
        request could not be honored.

### 7.26.4.4 [The mtx_timedlock function]

    1 Synopsis
              #include <threads.h>
               int mtx_timedlock(mtx_t *restrict mtx,
                    const struct timespec *restrict ts);
        Description

    2   The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
        mtx or until after the TIME_UTC-based calendar time pointed to by ts. The specified
        mutex shall support timeout. If the operation succeeds, prior calls to mtx_unlock on
        the same mutex shall synchronize with this operation.
        Returns

    3   The mtx_timedlock function returns thrd_success on success, or
        thrd_timedout if the time specified was reached without acquiring the requested
        resource, or thrd_error if the request could not be honored.

### 7.26.4.5 [The mtx_trylock function]

    1 Synopsis
              #include <threads.h>
               int mtx_trylock(mtx_t *mtx);
        Description

    2   The mtx_trylock function endeavors to lock the mutex pointed to by mtx. If the ∗
        mutex is already locked, the function returns without blocking. If the operation succeeds,
        prior calls to mtx_unlock on the same mutex shall synchronize with this operation.
        Returns

    3   The mtx_trylock function returns thrd_success on success, or thrd_busy if
        the resource requested is already in use, or thrd_error if the request could not be
        honored.

### 7.26.4.6 [The mtx_unlock function]

    1 Synopsis
              #include <threads.h>
               int mtx_unlock(mtx_t *mtx);
        Description

    2   The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
        by mtx shall be locked by the calling thread.
        Returns

    3   The mtx_unlock function returns thrd_success on success or thrd_error if
        the request could not be honored.

### 7.26.5 [Thread functions]

### 7.26.5.1 [The thrd_create function]

    1 Synopsis
              #include <threads.h>
               int thrd_create(thrd_t *thr, thrd_start_t func,
                    void *arg);
        Description

    2   The thrd_create function creates a new thread executing func(arg). If the
        thrd_create function succeeds, it sets the object pointed to by thr to the identifier of
        the newly created thread. (A thread’s identifier may be reused for a different thread once
        the original thread has exited and either been detached or joined to another thread.) The
        completion of the thrd_create function synchronizes with the beginning of the
        execution of the new thread.
        Returns

    3   The thrd_create function returns thrd_success on success, or thrd_nomem if
        no memory could be allocated for the thread requested, or thrd_error if the request
        could not be honored.

### 7.26.5.2 [The thrd_current function]

    1 Synopsis
              #include <threads.h>
               thrd_t thrd_current(void);
        Description

    2   The thrd_current function identifies the thread that called it.
        Returns

    3   The thrd_current function returns the identifier of the thread that called it.

### 7.26.5.3 [The thrd_detach function]

    1 Synopsis
              #include <threads.h>
               int thrd_detach(thrd_t thr);
        Description

    2   The thrd_detach function tells the operating system to dispose of any resources
        allocated to the thread identified by thr when that thread terminates. The thread
        identified by thr shall not have been previously detached or joined with another thread.
        Returns

    3   The thrd_detach function returns thrd_success on success or thrd_error if
        the request could not be honored.

### 7.26.5.4 [The thrd_equal function]

    1 Synopsis
              #include <threads.h>
               int thrd_equal(thrd_t thr0, thrd_t thr1);
        Description

    2   The thrd_equal function will determine whether the thread identified by thr0 refers
        to the thread identified by thr1.
        Returns

    3   The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
        different threads. Otherwise the thrd_equal function returns a nonzero value.

### 7.26.5.5 [The thrd_exit function]

    1 Synopsis
              #include <threads.h>
               _Noreturn void thrd_exit(int res);
        Description

    2   The thrd_exit function terminates execution of the calling thread and sets its result
        code to res.

    3   The program shall terminate normally after the last thread has been terminated. The
        behavior shall be as if the program called the exit function with the status
        EXIT_SUCCESS at thread termination time.
        Returns

    4   The thrd_exit function returns no value.

### 7.26.5.6 [The thrd_join function]

    1 Synopsis
              #include <threads.h>
               int thrd_join(thrd_t thr, int *res);
        Description

    2   The thrd_join function joins the thread identified by thr with the current thread by
        blocking until the other thread has terminated. If the parameter res is not a null pointer,
        it stores the thread’s result code in the integer pointed to by res. The termination of the
        other thread synchronizes with the completion of the thrd_join function. The thread
        identified by thr shall not have been previously detached or joined with another thread.
        Returns

    3   The thrd_join function returns thrd_success on success or thrd_error if the
        request could not be honored.

### 7.26.5.7 [The thrd_sleep function]

    1 Synopsis
              #include <threads.h>
               int thrd_sleep(const struct timespec *duration,
                    struct timespec *remaining);
        Description

    2   The thrd_sleep function suspends execution of the calling thread until either the
        interval specified by duration has elapsed or a signal which is not being ignored is
        received. If interrupted by a signal and the remaining argument is not null, the
        amount of time remaining (the requested interval minus the time actually slept) is stored
        in the interval it points to. The duration and remaining arguments may point to the
        same object.

    3   The suspension time may be longer than requested because the interval is rounded up to
        an integer multiple of the sleep resolution or because of the scheduling of other activity
        by the system. But, except for the case of being interrupted by a signal, the suspension
        time shall not be less than that specified, as measured by the system clock TIME_UTC.
        Returns

    4   The thrd_sleep function returns zero if the requested time has elapsed, -1 if it has
        been interrupted by a signal, or a negative value if it fails.

### 7.26.5.8 [The thrd_yield function]

    1 Synopsis
              #include <threads.h>
               void thrd_yield(void);
        Description

    2   The thrd_yield function endeavors to permit other threads to run, even if the current
        thread would ordinarily continue to run.
        Returns

    3   The thrd_yield function returns no value.

### 7.26.6 [Thread-specific storage functions]

### 7.26.6.1 [The tss_create function]

    1 Synopsis
              #include <threads.h>
               int tss_create(tss_t *key, tss_dtor_t dtor);
        Description

    2   The tss_create function creates a thread-specific storage pointer with destructor
        dtor, which may be null.
        Returns

    3   If the tss_create function is successful, it sets the thread-specific storage pointed to
        by key to a value that uniquely identifies the newly created pointer and returns
        thrd_success; otherwise, thrd_error is returned and the thread-specific storage
        pointed to by key is set to an undefined value.

### 7.26.6.2 [The tss_delete function]

    1 Synopsis
              #include <threads.h>
               void tss_delete(tss_t key);
        Description

    2   The tss_delete function releases any resources used by the thread-specific storage
        identified by key.
        Returns

    3   The tss_delete function returns no value.

### 7.26.6.3 [The tss_get function]

    1 Synopsis
              #include <threads.h>
               void *tss_get(tss_t key);
        Description

    2   The tss_get function returns the value for the current thread held in the thread-specific
        storage identified by key.
        Returns

    3   The tss_get function returns the value for the current thread if successful, or zero if
        unsuccessful.

### 7.26.6.4 [The tss_set function]

    1 Synopsis
              #include <threads.h>
               int tss_set(tss_t key, void *val);
        Description

    2   The tss_set function sets the value for the current thread held in the thread-specific
        storage identified by key to val.
        Returns

    3   The tss_set function returns thrd_success on success or thrd_error if the
        request could not be honored.                                             ∗

### 7.27 [Date and time <time.h>]

### 7.27.1 [Components of time]

    1   The header <time.h> defines two macros, and declares several types and functions for
        manipulating time. Many functions deal with a calendar time that represents the current
        date (according to the Gregorian calendar) and time. Some functions deal with local
        time, which is the calendar time expressed for some specific time zone, and with Daylight
        Saving Time, which is a temporary change in the algorithm for determining local time.
        The local time zone and Daylight Saving Time are implementation-defined.

    2   The macros defined are NULL (described in 7.19);                                                            ∗
                CLOCKS_PER_SEC
        which expands to an expression with type clock_t (described below) that is the
        number per second of the value returned by the clock function; and
                TIME_UTC
        which expands to an integer constant greater than 0 that designates the UTC time
        base.[316]

    Footnote 316) Implementations may define additional time bases, but are only required to support a real time clock
             based on UTC.

    3   The types declared are size_t (described in 7.19);
                clock_t
        and
                time_t
        which are real types capable of representing times;
                struct timespec
        which holds an interval specified in seconds and nanoseconds (which may represent a
        calendar time based on a particular epoch); and
                struct tm
        which holds the components of a calendar time, called the broken-down time.

    4   The range and precision of times representable in clock_t and time_t are
        implementation-defined. The timespec structure shall contain at least the following
        members, in any order.[317]
                time_t tv_sec; // whole seconds — ≥ 0
                long   tv_nsec; // nanoseconds — [0, 999999999]
        The tm structure shall contain at least the following members, in any order. The
        semantics of the members and their normal ranges are expressed in the comments.[318]
                int tm_sec;   // seconds after the minute — [0, 60]
                int tm_min;   // minutes after the hour — [0, 59]
                int tm_hour; // hours since midnight — [0, 23]
                int tm_mday; // day of the month — [1, 31]
                int tm_mon;   // months since January — [0, 11]
                int tm_year; // years since 1900
                int tm_wday; // days since Sunday — [0, 6]
                int tm_yday; // days since January 1 — [0, 365]
                int tm_isdst; // Daylight Saving Time flag
        The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
        Saving Time is not in effect, and negative if the information is not available.

    Footnote 317) The tv_sec member is a linear count of seconds and may not have the normal semantics of a
             time_t. The semantics of the members and their normal ranges are expressed in the comments.

    Footnote 318) The range [0, 60] for tm_sec allows for a positive leap second.

### 7.27.2 [Time manipulation functions]

### 7.27.2.1 [The clock function]

    1 Synopsis
               #include <time.h>
                clock_t clock(void);
        Description

    2   The clock function determines the processor time used.
        Returns

    3   The clock function returns the implementation’s best approximation to the processor
        time used by the program since the beginning of an implementation-defined era related
        only to the program invocation. To determine the time in seconds, the value returned by
        the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
        the processor time used is not available or its value cannot be represented, the function
        returns the value (clock_t)(-1).[319]

    Footnote 319) In order to measure the time spent in a program, the clock function should be called at the start of
             the program and its return value subtracted from the value returned by subsequent calls.

### 7.27.2.2 [The difftime function]

    1 Synopsis
               #include <time.h>
                double difftime(time_t time1, time_t time0);
        Description

    2   The difftime function computes the difference between two calendar times: time1 -
        time0.
        Returns

    3   The difftime function returns the difference expressed in seconds as a double.

### 7.27.2.3 [The mktime function]

    1 Synopsis
               #include <time.h>
                time_t mktime(struct tm *timeptr);
        Description

    2   The mktime function converts the broken-down time, expressed as local time, in the
        structure pointed to by timeptr into a calendar time value with the same encoding as
        that of the values returned by the time function. The original values of the tm_wday
        and tm_yday components of the structure are ignored, and the original values of the
        other components are not restricted to the ranges indicated above.[320] On successful
        completion, the values of the tm_wday and tm_yday components of the structure are
        set appropriately, and the other components are set to represent the specified calendar
        time, but with their values forced to the ranges indicated above; the final value of
        tm_mday is not set until tm_mon and tm_year are determined.
        Returns

    Footnote 320) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
             Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
             causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.

    3   The mktime function returns the specified calendar time encoded as a value of type
        time_t. If the calendar time cannot be represented, the function returns the value
        (time_t)(-1).

    4   EXAMPLE       What day of the week is July 4, 2001?
               #include <stdio.h>
               #include <time.h>
               static const char *const wday[] = {
                       "Sunday", "Monday", "Tuesday", "Wednesday",
                       "Thursday", "Friday", "Saturday", "-unknown-"
               };
               struct tm time_str;
               /* ... */
               time_str.tm_year   = 2001 - 1900;
               time_str.tm_mon    = 7 - 1;
               time_str.tm_mday   = 4;
               time_str.tm_hour   = 0;
               time_str.tm_min    = 0;
               time_str.tm_sec    = 1;
               time_str.tm_isdst = -1;
               if (mktime(&time_str) == (time_t)(-1))
                     time_str.tm_wday = 7;
               printf("%s\n", wday[time_str.tm_wday]);

### 7.27.2.4 [The time function]

    1 Synopsis
              #include <time.h>
               time_t time(time_t *timer);
        Description

    2   The time function determines the current calendar time. The encoding of the value is
        unspecified.
        Returns

    3   The time function returns the implementation’s best approximation to the current
        calendar time. The value (time_t)(-1) is returned if the calendar time is not
        available. If timer is not a null pointer, the return value is also assigned to the object it
        points to.

### 7.27.2.5 [The timespec_get function]

    1 Synopsis
              #include <time.h>
               int timespec_get(struct timespec *ts, int base);
        Description

    2   The timespec_get function sets the interval pointed to by ts to hold the current
        calendar time based on the specified time base.

    3   If base is TIME_UTC, the tv_sec member is set to the number of seconds since an
        implementation defined epoch, truncated to a whole value and the tv_nsec member is
        set to the integral number of nanoseconds, rounded to the resolution of the system
        clock.[321]
        Returns

    Footnote 321) Although a struct timespec object describes times with nanosecond resolution, the available
             resolution is system dependent and may even be greater than 1 second.

    4   If the timespec_get function is successful it returns the nonzero value base;
        otherwise, it returns zero.

### 7.27.3 [Time conversion functions]

    1   Except for the strftime function, these functions each return a pointer to one of two
        types of static objects: a broken-down time structure or an array of char. Execution of
        any of the functions that return a pointer to one of these object types may overwrite the
        information in any object of the same type pointed to by the value returned from any
        previous call to any of them and the functions are not required to avoid data races with
        each other.[322] The implementation shall behave as if no other library functions call these
        functions.

    Footnote 322) Alternative time conversion functions that do avoid data races are specified in K.3.8.2.

### 7.27.3.1 [The asctime function]

    1 Synopsis
                #include <time.h>
                 char *asctime(const struct tm *timeptr);
        Description

    2   The asctime function converts the broken-down time in the structure pointed to by
        timeptr into a string in the form
                 Sun Sep 16 01:03:52 1973\n\0
        using the equivalent of the following algorithm.
        char *asctime(const struct tm *timeptr)
        {
             static const char wday_name[7][3] = {
                  "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
             };
             static const char mon_name[12][3] = {
                  "Jan", "Feb", "Mar", "Apr", "May", "Jun",
                  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
             };
             static char result[26];
                sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
                     wday_name[timeptr->tm_wday],
                     mon_name[timeptr->tm_mon],
                     timeptr->tm_mday, timeptr->tm_hour,
                     timeptr->tm_min, timeptr->tm_sec,
                     1900 + timeptr->tm_year);
                return result;
        }

    3   If any of the members of the broken-down time contain values that are outside their
        normal ranges,[323] the behavior of the asctime function is undefined. Likewise, if the
        calculated year exceeds four digits or is less than the year 1000, the behavior is
        undefined.
        Returns

    Footnote 323) See 7.27.1.

    4   The asctime function returns a pointer to the string.

### 7.27.3.2 [The ctime function]

    1 Synopsis
               #include <time.h>
                char *ctime(const time_t *timer);
        Description

    2   The ctime function converts the calendar time pointed to by timer to local time in the
        form of a string. It is equivalent to
                asctime(localtime(timer))
        Returns

    3   The ctime function returns the pointer returned by the asctime function with that
        broken-down time as argument.
        Forward references: the localtime function (7.27.3.4).

### 7.27.3.3 [The gmtime function]

    1 Synopsis
               #include <time.h>
                struct tm *gmtime(const time_t *timer);
        Description

    2   The gmtime function converts the calendar time pointed to by timer into a broken-
        down time, expressed as UTC.
        Returns

    3   The gmtime function returns a pointer to the broken-down time, or a null pointer if the
        specified time cannot be converted to UTC.

### 7.27.3.4 [The localtime function]

    1 Synopsis
              #include <time.h>
               struct tm *localtime(const time_t *timer);
        Description

    2   The localtime function converts the calendar time pointed to by timer into a
        broken-down time, expressed as local time.
        Returns

    3   The localtime function returns a pointer to the broken-down time, or a null pointer if
        the specified time cannot be converted to local time.

### 7.27.3.5 [The strftime function]

    1 Synopsis
              #include <time.h>
               size_t strftime(char * restrict s,
                    size_t maxsize,
                    const char * restrict format,
                    const struct tm * restrict timeptr);
        Description

    2   The strftime function places characters into the array pointed to by s as controlled by
        the string pointed to by format. The format shall be a multibyte character sequence,
        beginning and ending in its initial shift state. The format string consists of zero or
        more conversion specifiers and ordinary multibyte characters. A conversion specifier
        consists of a % character, possibly followed by an E or O modifier character (described
        below), followed by a character that determines the behavior of the conversion specifier.
        All ordinary multibyte characters (including the terminating null character) are copied
        unchanged into the array. If copying takes place between objects that overlap, the
        behavior is undefined. No more than maxsize characters are placed into the array.

    3   Each conversion specifier is replaced by appropriate characters as described in the
        following list. The appropriate characters are determined using the LC_TIME category
    of the current locale and by the values of zero or more members of the broken-down time
    structure pointed to by timeptr, as specified in brackets in the description. If any of
    the specified values is outside the normal range, the characters stored are unspecified.
    %a   is replaced by the locale’s abbreviated weekday name. [tm_wday]
    %A   is replaced by the locale’s full weekday name. [tm_wday]
    %b   is replaced by the locale’s abbreviated month name. [tm_mon]
    %B   is replaced by the locale’s full month name. [tm_mon]
    %c   is replaced by the locale’s appropriate date and time representation. [all specified
         in 7.27.1]
    %C   is replaced by the year divided by 100 and truncated to an integer, as a decimal
         number (00−99). [tm_year]
    %d   is replaced by the day of the month as a decimal number (01−31). [tm_mday]
    %D   is equivalent to ‘‘%m/%d/%y’’. [tm_mon, tm_mday, tm_year]
    %e   is replaced by the day of the month as a decimal number (1−31); a single digit is
         preceded by a space. [tm_mday]
    %F   is equivalent to ‘‘%Y−%m−%d’’ (the ISO 8601 date format). [tm_year, tm_mon,
         tm_mday]
    %g   is replaced by the last 2 digits of the week-based year (see below) as a decimal
         number (00−99). [tm_year, tm_wday, tm_yday]
    %G   is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
         [tm_year, tm_wday, tm_yday]
    %h   is equivalent to ‘‘%b’’. [tm_mon]
    %H   is replaced by the hour (24-hour clock) as a decimal number (00−23). [tm_hour]
    %I   is replaced by the hour (12-hour clock) as a decimal number (01−12). [tm_hour]
    %j   is replaced by the day of the year as a decimal number (001−366). [tm_yday]
    %m   is replaced by the month as a decimal number (01−12). [tm_mon]
    %M   is replaced by the minute as a decimal number (00−59). [tm_min]
    %n   is replaced by a new-line character.
    %p   is replaced by the locale’s equivalent of the AM/PM designations associated with a
         12-hour clock. [tm_hour]
    %r   is replaced by the locale’s 12-hour clock time. [tm_hour, tm_min, tm_sec]
    %R   is equivalent to ‘‘%H:%M’’. [tm_hour, tm_min]
    %S   is replaced by the second as a decimal number (00−60). [tm_sec]
    %t   is replaced by a horizontal-tab character.
    %T   is equivalent to ‘‘%H:%M:%S’’ (the ISO 8601 time format). [tm_hour, tm_min,
         tm_sec]
    %u   is replaced by the ISO 8601 weekday as a decimal number (1−7), where Monday
         is 1. [tm_wday]
    %U   is replaced by the week number of the year (the first Sunday as the first day of week
         1) as a decimal number (00−53). [tm_year, tm_wday, tm_yday]
    %V   is replaced by the ISO 8601 week number (see below) as a decimal number
              (01−53). [tm_year, tm_wday, tm_yday]
        %w    is replaced by the weekday as a decimal number (0−6), where Sunday is 0.
              [tm_wday]
        %W    is replaced by the week number of the year (the first Monday as the first day of
              week 1) as a decimal number (00−53). [tm_year, tm_wday, tm_yday]
        %x    is replaced by the locale’s appropriate date representation. [all specified in 7.27.1]
        %X    is replaced by the locale’s appropriate time representation. [all specified in 7.27.1]
        %y    is replaced by the last 2 digits of the year as a decimal number (00−99).
              [tm_year]
        %Y    is replaced by the year as a decimal number (e.g., 1997). [tm_year]
        %z    is replaced by the offset from UTC in the ISO 8601 format ‘‘−0430’’ (meaning 4
              hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
              zone is determinable. [tm_isdst]
        %Z    is replaced by the locale’s time zone name or abbreviation, or by no characters if no
              time zone is determinable. [tm_isdst]
        %%    is replaced by %.

    4   Some conversion specifiers can be modified by the inclusion of an E or O modifier
        character to indicate an alternative format or specification. If the alternative format or
        specification does not exist for the current locale, the modifier is ignored.
        %Ec is replaced by the locale’s alternative date and time representation.
        %EC is replaced by the name of the base year (period) in the locale’s alternative
            representation.
        %Ex is replaced by the locale’s alternative date representation.
        %EX is replaced by the locale’s alternative time representation.
        %Ey is replaced by the offset from %EC (year only) in the locale’s alternative
            representation.
        %EY is replaced by the locale’s full alternative year representation.
        %Od is replaced by the day of the month, using the locale’s alternative numeric symbols
            (filled as needed with leading zeros, or with leading spaces if there is no alternative
            symbol for zero).
        %Oe is replaced by the day of the month, using the locale’s alternative numeric symbols
            (filled as needed with leading spaces).
        %OH is replaced by the hour (24-hour clock), using the locale’s alternative numeric
            symbols.
        %OI is replaced by the hour (12-hour clock), using the locale’s alternative numeric
            symbols.
        %Om is replaced by the month, using the locale’s alternative numeric symbols.
        %OM is replaced by the minutes, using the locale’s alternative numeric symbols.
        %OS is replaced by the seconds, using the locale’s alternative numeric symbols.
        %Ou is replaced by the ISO 8601 weekday as a number in the locale’s alternative
            representation, where Monday is 1.
        %OU is replaced by the week number, using the locale’s alternative numeric symbols.
        %OV is replaced by the ISO 8601 week number, using the locale’s alternative numeric
            symbols.
        %Ow is replaced by the weekday as a number, using the locale’s alternative numeric
            symbols.
        %OW is replaced by the week number of the year, using the locale’s alternative numeric
            symbols.
        %Oy is replaced by the last 2 digits of the year, using the locale’s alternative numeric
            symbols.

    5   %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
        weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
        which is also the week that includes the first Thursday of the year, and is also the first
        week that contains at least four days in the year. If the first Monday of January is the
        2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
        for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
        December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
        the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
        %V is replaced by 01.

    6   If a conversion specifier is not one of the above, the behavior is undefined.

    7   In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
        following specifiers are:
        %a    the first three characters of %A.
        %A    one of ‘‘Sunday’’, ‘‘Monday’’, ... , ‘‘Saturday’’.
        %b    the first three characters of %B.
        %B    one of ‘‘January’’, ‘‘February’’, ... , ‘‘December’’.
        %c    equivalent to ‘‘%a %b %e %T %Y’’.
        %p    one of ‘‘AM’’ or ‘‘PM’’.
        %r    equivalent to ‘‘%I:%M:%S %p’’.
        %x    equivalent to ‘‘%m/%d/%y’’.
        %X    equivalent to %T.
        %Z    implementation-defined.
        Returns

    8   If the total number of resulting characters including the terminating null character is not
        more than maxsize, the strftime function returns the number of characters placed
        into the array pointed to by s not including the terminating null character. Otherwise,
        zero is returned and the contents of the array are indeterminate.

### 7.28 [Unicode utilities <uchar.h>]

    1   The header <uchar.h> declares types and functions for manipulating Unicode
        characters.

    2   The types declared are mbstate_t (described in 7.30.1) and size_t (described in
        7.19);
               char16_t
        which is an unsigned integer type used for 16-bit characters and is the same type as
        uint_least16_t (described in 7.20.1.2); and
               char32_t
        which is an unsigned integer type used for 32-bit characters and is the same type as
        uint_least32_t (also described in 7.20.1.2).

### 7.28.1 [Restartable multibyte/wide character conversion functions]

    1   These functions have a parameter, ps, of type pointer to mbstate_t that points to an
        object that can completely describe the current conversion state of the associated
        multibyte character sequence, which the functions alter as necessary. If ps is a null
        pointer, each function uses its own internal mbstate_t object instead, which is
        initialized at program startup to the initial conversion state; the functions are not required
        to avoid data races with other calls to the same function in this case. The implementation
        behaves as if no library function calls these functions with a null pointer for ps.

### 7.28.1.1 [The mbrtoc16 function]

    1 Synopsis
              #include <uchar.h>
               size_t mbrtoc16(char16_t * restrict pc16,
                    const char * restrict s, size_t n,
                    mbstate_t * restrict ps);
        Description

    2   If s is a null pointer, the mbrtoc16 function is equivalent to the call:
                       mbrtoc16(NULL, "", 1, ps)
        In this case, the values of the parameters pc16 and n are ignored.

    3   If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
        the byte pointed to by s to determine the number of bytes needed to complete the next
        multibyte character (including any shift sequences). If the function determines that the
        next multibyte character is complete and valid, it determines the values of the
        corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
        the first (or only) such character in the object pointed to by pc16. Subsequent calls will
        store successive wide characters without consuming any additional input until all the
        characters have been stored. If the corresponding wide character is the null wide
        character, the resulting state described is the initial conversion state.
        Returns

    4   The mbrtoc16 function returns the first of the following that applies (given the current
        conversion state):
        0                     if the next n or fewer bytes complete the multibyte character that
                              corresponds to the null wide character (which is the value stored).
        between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                           character (which is the value stored); the value returned is the number
                           of bytes that complete the multibyte character.
        (size_t)(-3) if the next character resulting from a previous call has been stored (no
                     bytes from the input have been consumed by this call).
        (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                     multibyte character, and all n bytes have been processed (no value is
                     stored).[324]
        (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                     do not contribute to a complete and valid multibyte character (no
                     value is stored); the value of the macro EILSEQ is stored in errno,
                     and the conversion state is unspecified.

    Footnote 324) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
             sequence of redundant shift sequences (for implementations with state-dependent encodings).

### 7.28.1.2 [The c16rtomb function]

    1 Synopsis
               #include <uchar.h>
                size_t c16rtomb(char * restrict s, char16_t c16,
                     mbstate_t * restrict ps);
        Description

    2   If s is a null pointer, the c16rtomb function is equivalent to the call
                        c16rtomb(buf, L'\0', ps)
        where buf is an internal buffer.

    3   If s is not a null pointer, the c16rtomb function determines the number of bytes needed
        to represent the multibyte character that corresponds to the wide character given by c16
        (including any shift sequences), and stores the multibyte character representation in the
        array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
        c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
        to restore the initial shift state; the resulting state described is the initial conversion state.
        Returns

    4   The c16rtomb function returns the number of bytes stored in the array object (including
        any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
        the function stores the value of the macro EILSEQ in errno and returns
        (size_t)(-1); the conversion state is unspecified.

### 7.28.1.3 [The mbrtoc32 function]

    1 Synopsis
               #include <uchar.h>
                size_t mbrtoc32(char32_t * restrict pc32,
                     const char * restrict s, size_t n,
                     mbstate_t * restrict ps);
        Description

    2   If s is a null pointer, the mbrtoc32 function is equivalent to the call:
                        mbrtoc32(NULL, "", 1, ps)
        In this case, the values of the parameters pc32 and n are ignored.

    3   If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
        the byte pointed to by s to determine the number of bytes needed to complete the next
        multibyte character (including any shift sequences). If the function determines that the
        next multibyte character is complete and valid, it determines the values of the
        corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
        the first (or only) such character in the object pointed to by pc32. Subsequent calls will
        store successive wide characters without consuming any additional input until all the
        characters have been stored. If the corresponding wide character is the null wide
        character, the resulting state described is the initial conversion state.
        Returns

    4   The mbrtoc32 function returns the first of the following that applies (given the current
        conversion state):
        0                    if the next n or fewer bytes complete the multibyte character that
                             corresponds to the null wide character (which is the value stored).
        between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                           character (which is the value stored); the value returned is the number
                           of bytes that complete the multibyte character.
        (size_t)(-3) if the next character resulting from a previous call has been stored (no
                     bytes from the input have been consumed by this call).
        (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                     multibyte character, and all n bytes have been processed (no value is
                     stored).[325]
        (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                     do not contribute to a complete and valid multibyte character (no
                     value is stored); the value of the macro EILSEQ is stored in errno,
                     and the conversion state is unspecified.

    Footnote 325) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
             sequence of redundant shift sequences (for implementations with state-dependent encodings).

### 7.28.1.4 [The c32rtomb function]

    1 Synopsis
               #include <uchar.h>
                size_t c32rtomb(char * restrict s, char32_t c32,
                     mbstate_t * restrict ps);
        Description

    2   If s is a null pointer, the c32rtomb function is equivalent to the call
                        c32rtomb(buf, L'\0', ps)
        where buf is an internal buffer.

    3   If s is not a null pointer, the c32rtomb function determines the number of bytes needed
        to represent the multibyte character that corresponds to the wide character given by c32
        (including any shift sequences), and stores the multibyte character representation in the
        array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
        c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
        to restore the initial shift state; the resulting state described is the initial conversion state.
        Returns

    4   The c32rtomb function returns the number of bytes stored in the array object (including
        any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
        the function stores the value of the macro EILSEQ in errno and returns
        (size_t)(-1); the conversion state is unspecified.

### 7.29 [Extended multibyte and wide character utilities <wchar.h>]

### 7.29.1 [Introduction]

    1   The header <wchar.h> defines four macros, and declares four data types, one tag, and
        many functions.[326]

    Footnote 326) See ‘‘future library directions’’ (7.31.16).

    2   The types declared are wchar_t and size_t (both described in 7.19);
                 mbstate_t
        which is a complete object type other than an array type that can hold the conversion state
        information necessary to convert between sequences of multibyte characters and wide
        characters;
                 wint_t
        which is an integer type unchanged by default argument promotions that can hold any
        value corresponding to members of the extended character set, as well as at least one
        value that does not correspond to any member of the extended character set (see WEOF
        below);[327] and
                 struct tm
        which is declared as an incomplete structure type (the contents are described in 7.27.1).

    Footnote 327) wchar_t and wint_t can be the same integer type.

    3   The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
        (described in 7.20.3); and
                 WEOF
        which expands to a constant expression of type wint_t whose value does not
        correspond to any member of the extended character set.[328] It is accepted (and returned)
        by several functions in this subclause to indicate end-of-file, that is, no more input from a
        stream. It is also used as a wide character value that does not correspond to any member
        of the extended character set.

    Footnote 328) The value of the macro WEOF may differ from that of EOF and need not be negative.

    4   The functions declared are grouped as follows:
        — Functions that perform input and output of wide characters, or multibyte characters,
          or both;
        — Functions that provide wide string numeric conversion;
        — Functions that perform general wide string manipulation;
        — Functions for wide string date and time conversion; and
        — Functions that provide extended capabilities for conversion between multibyte and
          wide character sequences.

    5   Arguments to the functions in this subclause may point to arrays containing wchar_t
        values that do not correspond to members of the extended character set. Such values
        shall be processed according to the specified semantics, except that it is unspecified
        whether an encoding error occurs if such a value appears in the format string for a
        function in 7.29.2 or 7.29.5 and the specified semantics do not require that value to be
        processed by wcrtomb.

    6   Unless explicitly stated otherwise, if the execution of a function described in this
        subclause causes copying to take place between objects that overlap, the behavior is
        undefined.

### 7.29.2 [Formatted wide character input/output functions]

    1   The formatted wide character input/output functions shall behave as if there is a sequence
        point after the actions associated with each specifier.[329]

    Footnote 329) The fwprintf functions perform writes to memory for the %n specifier.

### 7.29.2.1 [The fwprintf function]

    1 Synopsis
               #include <stdio.h>
                #include <wchar.h>
                int fwprintf(FILE * restrict stream,
                     const wchar_t * restrict format, ...);
        Description

    2   The fwprintf function writes output to the stream pointed to by stream, under
        control of the wide string pointed to by format that specifies how subsequent arguments
        are converted for output. If there are insufficient arguments for the format, the behavior
        is undefined. If the format is exhausted while arguments remain, the excess arguments
        are evaluated (as always) but are otherwise ignored. The fwprintf function returns
        when the end of the format string is encountered.

    3   The format is composed of zero or more directives: ordinary wide characters (not %),
        which are copied unchanged to the output stream; and conversion specifications, each of
        which results in fetching zero or more subsequent arguments, converting them, if
        applicable, according to the corresponding conversion specifier, and then writing the
        result to the output stream.

    4   Each conversion specification is introduced by the wide character %. After the %, the
        following appear in sequence:
        — Zero or more flags (in any order) that modify the meaning of the conversion
          specification.
        — An optional minimum field width. If the converted value has fewer wide characters
          than the field width, it is padded with spaces (by default) on the left (or right, if the
          left adjustment flag, described later, has been given) to the field width. The field
          width takes the form of an asterisk * (described later) or a nonnegative decimal
          integer.[330]
        — An optional precision that gives the minimum number of digits to appear for the d, i,
          o, u, x, and X conversions, the number of digits to appear after the decimal-point
          wide character for a, A, e, E, f, and F conversions, the maximum number of
          significant digits for the g and G conversions, or the maximum number of wide
          characters to be written for s conversions. The precision takes the form of a period
          (.) followed either by an asterisk * (described later) or by an optional decimal
          integer; if only the period is specified, the precision is taken as zero. If a precision
          appears with any other conversion specifier, the behavior is undefined.
        — An optional length modifier that specifies the size of the argument.
        — A conversion specifier wide character that specifies the type of conversion to be
          applied.

    Footnote 330) Note that 0 is taken as a flag, not as the beginning of a field width.

    5   As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
        this case, an int argument supplies the field width or precision. The arguments
        specifying field width, or precision, or both, shall appear (in that order) before the
        argument (if any) to be converted. A negative field width argument is taken as a - flag
        followed by a positive field width. A negative precision argument is taken as if the
        precision were omitted.

    6   The flag wide characters and their meanings are:
        -        The result of the conversion is left-justified within the field. (It is right-justified if
                 this flag is not specified.)
        +        The result of a signed conversion always begins with a plus or minus sign. (It
                 begins with a sign only when a negative value is converted if this flag is not
                  specified.)[331]
        space If the first wide character of a signed conversion is not a sign, or if a signed
              conversion results in no wide characters, a space is prefixed to the result. If the
              space and + flags both appear, the space flag is ignored.
        #         The result is converted to an ‘‘alternative form’’. For o conversion, it increases
                  the precision, if and only if necessary, to force the first digit of the result to be a
                  zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
                  conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
                  and G conversions, the result of converting a floating-point number always
                  contains a decimal-point wide character, even if no digits follow it. (Normally, a
                  decimal-point wide character appears in the result of these conversions only if a
                  digit follows it.) For g and G conversions, trailing zeros are not removed from the
                  result. For other conversions, the behavior is undefined.
        0         For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
                  (following any indication of sign or base) are used to pad to the field width rather
                  than performing space padding, except when converting an infinity or NaN. If the
                  0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
                  conversions, if a precision is specified, the 0 flag is ignored. For other
                  conversions, the behavior is undefined.

    Footnote 331) The results of all floating conversions of a negative zero, and of negative values that round to zero,
             include a minus sign.

    7   The length modifiers and their meanings are:
        hh             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                       signed char or unsigned char argument (the argument will have
                       been promoted according to the integer promotions, but its value shall be
                       converted to signed char or unsigned char before printing); or that
                       a following n conversion specifier applies to a pointer to a signed char
                       argument.
        h              Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                       short int or unsigned short int argument (the argument will
                       have been promoted according to the integer promotions, but its value shall
                       be converted to short int or unsigned short int before printing);
                       or that a following n conversion specifier applies to a pointer to a short
                       int argument.
        l (ell)        Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                       long int or unsigned long int argument; that a following n
                       conversion specifier applies to a pointer to a long int argument; that a
                     following c conversion specifier applies to a wint_t argument; that a
                     following s conversion specifier applies to a pointer to a wchar_t
                     argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
                     specifier.
        ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                     long long int or unsigned long long int argument; or that a
                     following n conversion specifier applies to a pointer to a long long int
                     argument.
        j            Specifies that a following d, i, o, u, x, or X conversion specifier applies to
                     an intmax_t or uintmax_t argument; or that a following n conversion
                     specifier applies to a pointer to an intmax_t argument.
        z            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                     size_t or the corresponding signed integer type argument; or that a
                     following n conversion specifier applies to a pointer to a signed integer type
                     corresponding to size_t argument.
        t            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                     ptrdiff_t or the corresponding unsigned integer type argument; or that a
                     following n conversion specifier applies to a pointer to a ptrdiff_t
                     argument.
        L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                     applies to a long double argument.
        If a length modifier appears with any conversion specifier other than as specified above,
        the behavior is undefined.

    8   The conversion specifiers and their meanings are:
        d,i         The int argument is converted to signed decimal in the style [−]dddd. The
                    precision specifies the minimum number of digits to appear; if the value
                    being converted can be represented in fewer digits, it is expanded with
                    leading zeros. The default precision is 1. The result of converting a zero
                    value with a precision of zero is no wide characters.
        o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
                decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
                letters abcdef are used for x conversion and the letters ABCDEF for X
                conversion. The precision specifies the minimum number of digits to appear;
                if the value being converted can be represented in fewer digits, it is expanded
                with leading zeros. The default precision is 1. The result of converting a
                zero value with a precision of zero is no wide characters.
    f,F          A double argument representing a floating-point number is converted to
                 decimal notation in the style [−]ddd.ddd, where the number of digits after
                 the decimal-point wide character is equal to the precision specification. If the
                 precision is missing, it is taken as 6; if the precision is zero and the # flag is
                 not specified, no decimal-point wide character appears. If a decimal-point
                 wide character appears, at least one digit appears before it. The value is
                 rounded to the appropriate number of digits.
                 A double argument representing an infinity is converted in one of the styles
                 [-]inf or [-]infinity — which style is implementation-defined. A
                 double argument representing a NaN is converted in one of the styles
                 [-]nan or [-]nan(n-wchar-sequence) — which style, and the meaning of
                 any n-wchar-sequence, is implementation-defined. The F conversion
                 specifier produces INF, INFINITY, or NAN instead of inf, infinity, or
                 nan, respectively.[332]
    e,E          A double argument representing a floating-point number is converted in the
                 style [−]d.ddd e±dd, where there is one digit (which is nonzero if the
                 argument is nonzero) before the decimal-point wide character and the number
                 of digits after it is equal to the precision; if the precision is missing, it is taken
                 as 6; if the precision is zero and the # flag is not specified, no decimal-point
                 wide character appears. The value is rounded to the appropriate number of
                 digits. The E conversion specifier produces a number with E instead of e
                 introducing the exponent. The exponent always contains at least two digits,
                 and only as many more digits as necessary to represent the exponent. If the
                 value is zero, the exponent is zero.
                 A double argument representing an infinity or NaN is converted in the style
                 of an f or F conversion specifier.
    g,G          A double argument representing a floating-point number is converted in
                 style f or e (or in style F or E in the case of a G conversion specifier),
                 depending on the value converted and the precision. Let P equal the
                 precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
                 Then, if a conversion with style E would have an exponent of X:
                 — if P > X ≥ −4, the conversion is with style f (or F) and precision
                   P − (X + 1).
                 — otherwise, the conversion is with style e (or E) and precision P − 1.
                 Finally, unless the # flag is used, any trailing zeros are removed from the
                 fractional portion of the result and the decimal-point wide character is
                 removed if there is no fractional portion remaining.
                 A double argument representing an infinity or NaN is converted in the style
                 of an f or F conversion specifier.
    a,A          A double argument representing a floating-point number is converted in the
                 style [−]0xh.hhhh p±d, where there is one hexadecimal digit (which is
                 nonzero if the argument is a normalized floating-point number and is
                 otherwise unspecified) before the decimal-point wide character[333] and the
                 number of hexadecimal digits after it is equal to the precision; if the precision
                 is missing and FLT_RADIX is a power of 2, then the precision is sufficient
                 for an exact representation of the value; if the precision is missing and
                 FLT_RADIX is not a power of 2, then the precision is sufficient to
                 distinguish[334] values of type double, except that trailing zeros may be
                 omitted; if the precision is zero and the # flag is not specified, no decimal-
                 point wide character appears. The letters abcdef are used for a conversion
                 and the letters ABCDEF for A conversion. The A conversion specifier
                 produces a number with X and P instead of x and p. The exponent always
                 contains at least one digit, and only as many more digits as necessary to
                 represent the decimal exponent of 2. If the value is zero, the exponent is
                 zero.
                 A double argument representing an infinity or NaN is converted in the style
                 of an f or F conversion specifier.
    c            If no l length modifier is present, the int argument is converted to a wide
                 character as if by calling btowc and the resulting wide character is written.
                 If an l length modifier is present, the wint_t argument is converted to
                 wchar_t and written.
    s            If no l length modifier is present, the argument shall be a pointer to the initial
                 element of a character array containing a multibyte character sequence
                 beginning in the initial shift state. Characters from the array are converted as
                 if by repeated calls to the mbrtowc function, with the conversion state
                 described by an mbstate_t object initialized to zero before the first
                 multibyte character is converted, and written up to (but not including) the
                        terminating null wide character. If the precision is specified, no more than
                        that many wide characters are written. If the precision is not specified or is
                        greater than the size of the converted array, the converted array shall contain a
                        null wide character.
                        If an l length modifier is present, the argument shall be a pointer to the initial
                        element of an array of wchar_t type. Wide characters from the array are
                        written up to (but not including) a terminating null wide character. If the
                        precision is specified, no more than that many wide characters are written. If
                        the precision is not specified or is greater than the size of the array, the array
                        shall contain a null wide character.
         p              The argument shall be a pointer to void. The value of the pointer is
                        converted to a sequence of printing wide characters, in an implementation-
                        defined manner.
         n              The argument shall be a pointer to signed integer into which is written the
                        number of wide characters written to the output stream so far by this call to
                        fwprintf. No argument is converted, but one is consumed. If the
                        conversion specification includes any flags, a field width, or a precision, the
                        behavior is undefined.
         %              A % wide character is written. No argument is converted. The complete
                        conversion specification shall be %%.

    Footnote 332) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
         meaning; the # and 0 flag wide characters have no effect.

    Footnote 333) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
         character so that subsequent digits align to nibble (4-bit) boundaries.

    Footnote 334) The precision p is sufficient to distinguish values of the source type if 16 p−1 > b n where b is
         FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
         might suffice depending on the implementation’s scheme for determining the digit to the left of the
         decimal-point wide character.

    9    If a conversion specification is invalid, the behavior is undefined.[335] If any argument is
         not the correct type for the corresponding conversion specification, the behavior is
         undefined.

    Footnote 335) See ‘‘future library directions’’ (7.31.16).

    10   In no case does a nonexistent or small field width cause truncation of a field; if the result
         of a conversion is wider than the field width, the field is expanded to contain the
         conversion result.

    11   For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
         to a hexadecimal floating number with the given precision.
         Recommended practice

    12   For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
         representable in the given precision, the result should be one of the two adjacent numbers
         in hexadecimal floating style with the given precision, with the extra stipulation that the
         error should have a correct sign for the current rounding direction.

    13   For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
         DECIMAL_DIG, then the result should be correctly rounded.[336] If the number of
         significant decimal digits is more than DECIMAL_DIG but the source value is exactly
         representable with DECIMAL_DIG digits, then the result should be an exact
         representation with trailing zeros. Otherwise, the source value is bounded by two
         adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
         of the resultant decimal string D should satisfy L ≤ D ≤ U, with the extra stipulation that
         the error should have a correct sign for the current rounding direction.
         Returns

    Footnote 336) For binary-to-decimal conversion, the result format’s values are the numbers representable with the
              given format specifier. The number of significant digits is determined by the format specifier, and in
              the case of fixed-point conversion by the source value as well.

    14   The fwprintf function returns the number of wide characters transmitted, or a negative
         value if an output or encoding error occurred.
         Environmental limits

    15   The number of wide characters that can be produced by any single conversion shall be at
         least 4095.

    16   EXAMPLE       To print a date and time in the form ‘‘Sunday, July 3, 10:02’’ followed by π to five decimal
         places:
                 #include <math.h>
                 #include <stdio.h>
                 #include <wchar.h>
                 /* ... */
                 wchar_t *weekday, *month; // pointers to wide strings
                 int day, hour, min;
                 fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
                         weekday, month, day, hour, min);
                 fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));

         Forward references:           the btowc function (7.29.6.1.1), the mbrtowc function
         (7.29.6.3.2).

### 7.29.2.2 [The fwscanf function]

    1 Synopsis
                #include <stdio.h>
                 #include <wchar.h>
                 int fwscanf(FILE * restrict stream,
                      const wchar_t * restrict format, ...);
         Description

    2    The fwscanf function reads input from the stream pointed to by stream, under
         control of the wide string pointed to by format that specifies the admissible input
         sequences and how they are to be converted for assignment, using subsequent arguments
        as pointers to the objects to receive the converted input. If there are insufficient
        arguments for the format, the behavior is undefined. If the format is exhausted while
        arguments remain, the excess arguments are evaluated (as always) but are otherwise
        ignored.

    3   The format is composed of zero or more directives: one or more white-space wide
        characters, an ordinary wide character (neither % nor a white-space wide character), or a
        conversion specification. Each conversion specification is introduced by the wide
        character %. After the %, the following appear in sequence:
        — An optional assignment-suppressing wide character *.
        — An optional decimal integer greater than zero that specifies the maximum field width
          (in wide characters).
        — An optional length modifier that specifies the size of the receiving object.
        — A conversion specifier wide character that specifies the type of conversion to be
          applied.

    4   The fwscanf function executes each directive of the format in turn. When all directives
        have been executed, or if a directive fails (as detailed below), the function returns.
        Failures are described as input failures (due to the occurrence of an encoding error or the
        unavailability of input characters), or matching failures (due to inappropriate input).

    5   A directive composed of white-space wide character(s) is executed by reading input up to
        the first non-white-space wide character (which remains unread), or until no more wide
        characters can be read. The directive never fails.

    6   A directive that is an ordinary wide character is executed by reading the next wide
        character of the stream. If that wide character differs from the directive, the directive
        fails and the differing and subsequent wide characters remain unread. Similarly, if end-
        of-file, an encoding error, or a read error prevents a wide character from being read, the
        directive fails.

    7   A directive that is a conversion specification defines a set of matching input sequences, as
        described below for each specifier. A conversion specification is executed in the
        following steps:

    8   Input white-space wide characters (as specified by the iswspace function) are skipped,
        unless the specification includes a [, c, or n specifier.[337]

    Footnote 337) These white-space wide characters are not counted against a specified field width.

    9   An input item is read from the stream, unless the specification includes an n specifier. An
        input item is defined as the longest sequence of input wide characters which does not
        exceed any specified field width and which is, or is a prefix of, a matching input
         sequence.[338] The first wide character, if any, after the input item remains unread. If the
         length of the input item is zero, the execution of the directive fails; this condition is a
         matching failure unless end-of-file, an encoding error, or a read error prevented input
         from the stream, in which case it is an input failure.

    Footnote 338) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
              sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.

    10   Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
         count of input wide characters) is converted to a type appropriate to the conversion
         specifier. If the input item is not a matching sequence, the execution of the directive fails:
         this condition is a matching failure. Unless assignment suppression was indicated by a *,
         the result of the conversion is placed in the object pointed to by the first argument
         following the format argument that has not already received a conversion result. If this
         object does not have an appropriate type, or if the result of the conversion cannot be
         represented in the object, the behavior is undefined.

    11   The length modifiers and their meanings are:
         hh           Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to signed char or unsigned char.
         h            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to short int or unsigned short
                      int.
         l (ell)      Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to long int or unsigned long
                      int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
                      an argument with type pointer to double; or that a following c, s, or [
                      conversion specifier applies to an argument with type pointer to wchar_t.
         ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to long long int or unsigned
                      long long int.
         j            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to intmax_t or uintmax_t.
         z            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to size_t or the corresponding signed
                      integer type.
         t            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                      to an argument with type pointer to ptrdiff_t or the corresponding
                      unsigned integer type.
         L           Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                     applies to an argument with type pointer to long double.
         If a length modifier appears with any conversion specifier other than as specified above,
         the behavior is undefined.

    12   The conversion specifiers and their meanings are:
         d          Matches an optionally signed decimal integer, whose format is the same as
                    expected for the subject sequence of the wcstol function with the value 10
                    for the base argument. The corresponding argument shall be a pointer to
                    signed integer.
         i          Matches an optionally signed integer, whose format is the same as expected
                    for the subject sequence of the wcstol function with the value 0 for the
                    base argument. The corresponding argument shall be a pointer to signed
                    integer.
         o          Matches an optionally signed octal integer, whose format is the same as
                    expected for the subject sequence of the wcstoul function with the value 8
                    for the base argument. The corresponding argument shall be a pointer to
                    unsigned integer.
         u          Matches an optionally signed decimal integer, whose format is the same as
                    expected for the subject sequence of the wcstoul function with the value 10
                    for the base argument. The corresponding argument shall be a pointer to
                    unsigned integer.
         x          Matches an optionally signed hexadecimal integer, whose format is the same
                    as expected for the subject sequence of the wcstoul function with the value
                    16 for the base argument. The corresponding argument shall be a pointer to
                    unsigned integer.
         a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
                 format is the same as expected for the subject sequence of the wcstod
                 function. The corresponding argument shall be a pointer to floating.
         c          Matches a sequence of wide characters of exactly the number specified by the
                    field width (1 if no field width is present in the directive).
                    If no l length modifier is present, characters from the input field are
                    converted as if by repeated calls to the wcrtomb function, with the
                    conversion state described by an mbstate_t object initialized to zero
                    before the first wide character is converted. The corresponding argument
                    shall be a pointer to the initial element of a character array large enough to
                    accept the sequence. No null character is added.
                    If an l length modifier is present, the corresponding argument shall be a
        pointer to the initial element of an array of wchar_t large enough to accept
        the sequence. No null wide character is added.
    s   Matches a sequence of non-white-space wide characters.
        If no l length modifier is present, characters from the input field are
        converted as if by repeated calls to the wcrtomb function, with the
        conversion state described by an mbstate_t object initialized to zero
        before the first wide character is converted. The corresponding argument
        shall be a pointer to the initial element of a character array large enough to
        accept the sequence and a terminating null character, which will be added
        automatically.
        If an l length modifier is present, the corresponding argument shall be a
        pointer to the initial element of an array of wchar_t large enough to accept
        the sequence and the terminating null wide character, which will be added
        automatically.
    [   Matches a nonempty sequence of wide characters from a set of expected
        characters (the scanset).
        If no l length modifier is present, characters from the input field are
        converted as if by repeated calls to the wcrtomb function, with the
        conversion state described by an mbstate_t object initialized to zero
        before the first wide character is converted. The corresponding argument
        shall be a pointer to the initial element of a character array large enough to
        accept the sequence and a terminating null character, which will be added
        automatically.
        If an l length modifier is present, the corresponding argument shall be a
        pointer to the initial element of an array of wchar_t large enough to accept
        the sequence and the terminating null wide character, which will be added
        automatically.
        The conversion specifier includes all subsequent wide characters in the
        format string, up to and including the matching right bracket (]). The wide
        characters between the brackets (the scanlist) compose the scanset, unless the
        wide character after the left bracket is a circumflex (^), in which case the
        scanset contains all wide characters that do not appear in the scanlist between
        the circumflex and the right bracket. If the conversion specifier begins with
        [] or [^], the right bracket wide character is in the scanlist and the next
        following right bracket wide character is the matching right bracket that ends
        the specification; otherwise the first following right bracket wide character is
        the one that ends the specification. If a - wide character is in the scanlist and
        is not the first, nor the second where the first wide character is a ^, nor the
                        last character, the behavior is implementation-defined.
         p              Matches an implementation-defined set of sequences, which should be the
                        same as the set of sequences that may be produced by the %p conversion of
                        the fwprintf function. The corresponding argument shall be a pointer to a
                        pointer to void. The input item is converted to a pointer value in an
                        implementation-defined manner. If the input item is a value converted earlier
                        during the same program execution, the pointer that results shall compare
                        equal to that value; otherwise the behavior of the %p conversion is undefined.
         n              No input is consumed. The corresponding argument shall be a pointer to
                        signed integer into which is to be written the number of wide characters read
                        from the input stream so far by this call to the fwscanf function. Execution
                        of a %n directive does not increment the assignment count returned at the
                        completion of execution of the fwscanf function. No argument is
                        converted, but one is consumed. If the conversion specification includes an
                        assignment-suppressing wide character or a field width, the behavior is
                        undefined.
         %              Matches a single % wide character; no conversion or assignment occurs. The
                        complete conversion specification shall be %%.

    13   If a conversion specification is invalid, the behavior is undefined.[339]

    Footnote 339) See ‘‘future library directions’’ (7.31.16).

    14   The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
         respectively, a, e, f, g, and x.

    15   Trailing white space (including new-line wide characters) is left unread unless matched
         by a directive. The success of literal matches and suppressed assignments is not directly
         determinable other than via the %n directive.
         Returns

    16   The fwscanf function returns the value of the macro EOF if an input failure occurs
         before the first conversion (if any) has completed. Otherwise, the function returns the
         number of input items assigned, which can be fewer than provided for, or even zero, in
         the event of an early matching failure.

    17   EXAMPLE 1       The call:
                  #include <stdio.h>
                  #include <wchar.h>
                  /* ... */
                  int n, i; float x; wchar_t name[50];
                  n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
         with the input line:
                  25 54.32E-1 thompson
         will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
         thompson\0.

    18   EXAMPLE 2        The call:
                  #include <stdio.h>
                  #include <wchar.h>
                  /* ... */
                  int i; float x; double y;
                  fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
         with input:
                  56789 0123 56a72
         will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value
         56.0. The next wide character read from the input stream will be a.

         Forward references: the wcstod, wcstof, and wcstold functions (7.29.4.1.1), the
         wcstol, wcstoll, wcstoul, and wcstoull functions (7.29.4.1.2), the wcrtomb
         function (7.29.6.3.3).

### 7.29.2.3 [The swprintf function]

    1 Synopsis
                 #include <wchar.h>
                  int swprintf(wchar_t * restrict s,
                       size_t n,
                       const wchar_t * restrict format, ...);
         Description

    2    The swprintf function is equivalent to fwprintf, except that the argument s
         specifies an array of wide characters into which the generated output is to be written,
         rather than written to a stream. No more than n wide characters are written, including a
         terminating null wide character, which is always added (unless n is zero).
         Returns

    3    The swprintf function returns the number of wide characters written in the array, not
         counting the terminating null wide character, or a negative value if an encoding error
         occurred or if n or more wide characters were requested to be written.

### 7.29.2.4 [The swscanf function]

    1 Synopsis
              #include <wchar.h>
               int swscanf(const wchar_t * restrict s,
                    const wchar_t * restrict format, ...);
        Description

    2   The swscanf function is equivalent to fwscanf, except that the argument s specifies a
        wide string from which the input is to be obtained, rather than from a stream. Reaching
        the end of the wide string is equivalent to encountering end-of-file for the fwscanf
        function.
        Returns

    3   The swscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the swscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.29.2.5 [The vfwprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               #include <wchar.h>
               int vfwprintf(FILE * restrict stream,
                    const wchar_t * restrict format,
                    va_list arg);
        Description

    2   The vfwprintf function is equivalent to fwprintf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vfwprintf function does not invoke the
        va_end macro.[340]
        Returns

    Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
             invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vfwprintf function returns the number of wide characters transmitted, or a
        negative value if an output or encoding error occurred.

    4   EXAMPLE       The following shows the use of the vfwprintf function in a general error-reporting
        routine.
               #include <stdarg.h>
               #include <stdio.h>
               #include <wchar.h>
               void error(char *function_name, wchar_t *format, ...)
               {
                     va_list args;
                        va_start(args, format);
                        // print out name of function causing error
                        fwprintf(stderr, L"ERROR in %s: ", function_name);
                        // print out remainder of message
                        vfwprintf(stderr, format, args);
                        va_end(args);
               }

### 7.29.2.6 [The vfwscanf function]

    1 Synopsis
              #include <stdarg.h>
               #include <stdio.h>
               #include <wchar.h>
               int vfwscanf(FILE * restrict stream,
                    const wchar_t * restrict format,
                    va_list arg);
        Description

    2   The vfwscanf function is equivalent to fwscanf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vfwscanf function does not invoke the
        va_end macro.[340]
        Returns

    Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
             invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vfwscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the vfwscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.29.2.7 [The vswprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <wchar.h>
               int vswprintf(wchar_t * restrict s,
                    size_t n,
                    const wchar_t * restrict format,
                    va_list arg);
        Description

    2   The vswprintf function is equivalent to swprintf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vswprintf function does not invoke the
        va_end macro.[340]
        Returns

    Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
             invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vswprintf function returns the number of wide characters written in the array, not
        counting the terminating null wide character, or a negative value if an encoding error
        occurred or if n or more wide characters were requested to be generated.

### 7.29.2.8 [The vswscanf function]

    1 Synopsis
              #include <stdarg.h>
               #include <wchar.h>
               int vswscanf(const wchar_t * restrict s,
                    const wchar_t * restrict format,
                    va_list arg);
        Description

    2   The vswscanf function is equivalent to swscanf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vswscanf function does not invoke the
        va_end macro.[340]
        Returns

    Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
             invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vswscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the vswscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.29.2.9 [The vwprintf function]

    1 Synopsis
              #include <stdarg.h>
               #include <wchar.h>
               int vwprintf(const wchar_t * restrict format,
                    va_list arg);
        Description

    2   The vwprintf function is equivalent to wprintf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vwprintf function does not invoke the
        va_end macro.[340]
        Returns

    Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
             invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vwprintf function returns the number of wide characters transmitted, or a negative
        value if an output or encoding error occurred.

### 7.29.2.10 [The vwscanf function]

    1 Synopsis
              #include <stdarg.h>
               #include <wchar.h>
               int vwscanf(const wchar_t * restrict format,
                    va_list arg);
        Description

    2   The vwscanf function is equivalent to wscanf, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vwscanf function does not invoke the
        va_end macro.[340]
        Returns

    Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
             invoke the va_arg macro, the value of arg after the return is indeterminate.

    3   The vwscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the vwscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.29.2.11 [The wprintf function]

    1 Synopsis
              #include <wchar.h>
               int wprintf(const wchar_t * restrict format, ...);
        Description

    2   The wprintf function is equivalent to fwprintf with the argument stdout
        interposed before the arguments to wprintf.
        Returns

    3   The wprintf function returns the number of wide characters transmitted, or a negative
        value if an output or encoding error occurred.

### 7.29.2.12 [The wscanf function]

    1 Synopsis
              #include <wchar.h>
               int wscanf(const wchar_t * restrict format, ...);
        Description

    2   The wscanf function is equivalent to fwscanf with the argument stdin interposed
        before the arguments to wscanf.
        Returns

    3   The wscanf function returns the value of the macro EOF if an input failure occurs
        before the first conversion (if any) has completed. Otherwise, the wscanf function
        returns the number of input items assigned, which can be fewer than provided for, or even
        zero, in the event of an early matching failure.

### 7.29.3 [Wide character input/output functions]

### 7.29.3.1 [The fgetwc function]

    1 Synopsis
              #include <stdio.h>
               #include <wchar.h>
               wint_t fgetwc(FILE *stream);
        Description

    2   If the end-of-file indicator for the input stream pointed to by stream is not set and a
        next wide character is present, the fgetwc function obtains that wide character as a
        wchar_t converted to a wint_t and advances the associated file position indicator for
        the stream (if defined).
        Returns

    3   If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
        of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
        the fgetwc function returns the next wide character from the input stream pointed to by
        stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
        function returns WEOF. If an encoding error occurs (including too few bytes), the value of
        the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.[341]

    Footnote 341) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
             Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.

### 7.29.3.2 [The fgetws function]

    1 Synopsis
               #include <stdio.h>
                #include <wchar.h>
                wchar_t *fgetws(wchar_t * restrict s,
                     int n, FILE * restrict stream);
        Description

    2   The fgetws function reads at most one less than the number of wide characters
        specified by n from the stream pointed to by stream into the array pointed to by s. No
        additional wide characters are read after a new-line wide character (which is retained) or
        after end-of-file. A null wide character is written immediately after the last wide
        character read into the array.
        Returns

    3   The fgetws function returns s if successful. If end-of-file is encountered and no
        characters have been read into the array, the contents of the array remain unchanged and a
        null pointer is returned. If a read or encoding error occurs during the operation, the array
        contents are indeterminate and a null pointer is returned.

### 7.29.3.3 [The fputwc function]

    1 Synopsis
               #include <stdio.h>
                #include <wchar.h>
                wint_t fputwc(wchar_t c, FILE *stream);
        Description

    2   The fputwc function writes the wide character specified by c to the output stream
        pointed to by stream, at the position indicated by the associated file position indicator
        for the stream (if defined), and advances the indicator appropriately. If the file cannot
        support positioning requests, or if the stream was opened with append mode, the
        character is appended to the output stream.
        Returns

    3   The fputwc function returns the wide character written. If a write error occurs, the
        error indicator for the stream is set and fputwc returns WEOF. If an encoding error
        occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.

### 7.29.3.4 [The fputws function]

    1 Synopsis
               #include <stdio.h>
                #include <wchar.h>
                int fputws(const wchar_t * restrict s,
                     FILE * restrict stream);
        Description

    2   The fputws function writes the wide string pointed to by s to the stream pointed to by
        stream. The terminating null wide character is not written.
        Returns

    3   The fputws function returns EOF if a write or encoding error occurs; otherwise, it
        returns a nonnegative value.

### 7.29.3.5 [The fwide function]

    1 Synopsis
               #include <stdio.h>
                #include <wchar.h>
                int fwide(FILE *stream, int mode);
        Description

    2   The fwide function determines the orientation of the stream pointed to by stream. If
        mode is greater than zero, the function first attempts to make the stream wide oriented. If
        mode is less than zero, the function first attempts to make the stream byte oriented.[342]
        Otherwise, mode is zero and the function does not alter the orientation of the stream.
        Returns

    Footnote 342) If the orientation of the stream has already been determined, fwide does not change it.

    3   The fwide function returns a value greater than zero if, after the call, the stream has
        wide orientation, a value less than zero if the stream has byte orientation, or zero if the
        stream has no orientation.

### 7.29.3.6 [The getwc function]

    1 Synopsis
              #include <stdio.h>
               #include <wchar.h>
               wint_t getwc(FILE *stream);
        Description

    2   The getwc function is equivalent to fgetwc, except that if it is implemented as a
        macro, it may evaluate stream more than once, so the argument should never be an
        expression with side effects.
        Returns

    3   The getwc function returns the next wide character from the input stream pointed to by
        stream, or WEOF.

### 7.29.3.7 [The getwchar function]

    1 Synopsis
              #include <wchar.h>
               wint_t getwchar(void);
        Description

    2   The getwchar function is equivalent to getwc with the argument stdin.
        Returns

    3   The getwchar function returns the next wide character from the input stream pointed to
        by stdin, or WEOF.

### 7.29.3.8 [The putwc function]

    1 Synopsis
              #include <stdio.h>
               #include <wchar.h>
               wint_t putwc(wchar_t c, FILE *stream);
        Description

    2   The putwc function is equivalent to fputwc, except that if it is implemented as a
        macro, it may evaluate stream more than once, so that argument should never be an
        expression with side effects.
        Returns

    3   The putwc function returns the wide character written, or WEOF.

### 7.29.3.9 [The putwchar function]

    1 Synopsis
              #include <wchar.h>
               wint_t putwchar(wchar_t c);
        Description

    2   The putwchar function is equivalent to putwc with the second argument stdout.
        Returns

    3   The putwchar function returns the character written, or WEOF.

### 7.29.3.10 [The ungetwc function]

    1 Synopsis
              #include <stdio.h>
               #include <wchar.h>
               wint_t ungetwc(wint_t c, FILE *stream);
        Description

    2   The ungetwc function pushes the wide character specified by c back onto the input
        stream pointed to by stream. Pushed-back wide characters will be returned by
        subsequent reads on that stream in the reverse order of their pushing. A successful
        intervening call (with the stream pointed to by stream) to a file positioning function
        (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
        stream. The external storage corresponding to the stream is unchanged.

    3   One wide character of pushback is guaranteed, even if the call to the ungetwc function
        follows just after a call to a formatted wide character input function fwscanf,
        vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
        on the same stream without an intervening read or file positioning operation on that
        stream, the operation may fail.

    4   If the value of c equals that of the macro WEOF, the operation fails and the input stream is
        unchanged.

    5   A successful call to the ungetwc function clears the end-of-file indicator for the stream.
        The value of the file position indicator for the stream after reading or discarding all
        pushed-back wide characters is the same as it was before the wide characters were pushed
        back. For a text or binary stream, the value of its file position indicator after a successful
        call to the ungetwc function is unspecified until all pushed-back wide characters are
        read or discarded.
        Returns

    6   The ungetwc function returns the wide character pushed back, or WEOF if the operation
        fails.

### 7.29.4 [General wide string utilities]

    1   The header <wchar.h> declares a number of functions useful for wide string
        manipulation. Various methods are used for determining the lengths of the arrays, but in
        all cases a wchar_t * argument points to the initial (lowest addressed) element of the
        array. If an array is accessed beyond the end of an object, the behavior is undefined.

    2   Where an argument declared as size_t n determines the length of the array for a
        function, n can have the value zero on a call to that function. Unless explicitly stated
        otherwise in the description of a particular function in this subclause, pointer arguments
        on such a call shall still have valid values, as described in 7.1.4. On such a call, a
        function that locates a wide character finds no occurrence, a function that compares two
        wide character sequences returns zero, and a function that copies wide characters copies
        zero wide characters.

### 7.29.4.1 [Wide string numeric conversion functions]

### 7.29.4.1.1 [The wcstod, wcstof, and wcstold functions]

    1 Synopsis
              #include <wchar.h>
               double wcstod(const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr);
               float wcstof(const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr);
               long double wcstold(const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr);
        Description

    2   The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
        string pointed to by nptr to double, float, and long double representation,
        respectively. First, they decompose the input string into three parts: an initial, possibly
        empty, sequence of white-space wide characters (as specified by the iswspace
        function), a subject sequence resembling a floating-point constant or representing an
        infinity or NaN; and a final wide string of one or more unrecognized wide characters,
        including the terminating null wide character of the input wide string. Then, they attempt
        to convert the subject sequence to a floating-point number, and return the result.

    3   The expected form of the subject sequence is an optional plus or minus sign, then one of
        the following:
        — a nonempty sequence of decimal digits optionally containing a decimal-point wide
          character, then an optional exponent part as defined for the corresponding single-byte
          characters in 6.4.4.2;
        — a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
          decimal-point wide character, then an optional binary exponent part as defined in
          6.4.4.2;
        — INF or INFINITY, or any other wide string equivalent except for case
        — NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
          case in the NAN part, where:
                     n-wchar-sequence:
                           digit
                           nondigit
                           n-wchar-sequence digit
                           n-wchar-sequence nondigit
        The subject sequence is defined as the longest initial subsequence of the input wide
        string, starting with the first non-white-space wide character, that is of the expected form.
        The subject sequence contains no wide characters if the input wide string is not of the
        expected form.

    4   If the subject sequence has the expected form for a floating-point number, the sequence of
        wide characters starting with the first digit or the decimal-point wide character
        (whichever occurs first) is interpreted as a floating constant according to the rules of
        6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
        if neither an exponent part nor a decimal-point wide character appears in a decimal
        floating point number, or if a binary exponent part does not appear in a hexadecimal
        floating point number, an exponent part of the appropriate type with value zero is
        assumed to follow the last digit in the string. If the subject sequence begins with a minus
        sign, the sequence is interpreted as negated.[343] A wide character sequence INF or
        INFINITY is interpreted as an infinity, if representable in the return type, else like a
        floating constant that is too large for the range of the return type. A wide character
        sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
        in the return type, else like a subject sequence part that does not have the expected form;
        the meaning of the n-wchar sequence is implementation-defined.[344] A pointer to the
         final wide string is stored in the object pointed to by endptr, provided that endptr is
         not a null pointer.

    Footnote 343) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
             negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
             methods may yield different results if rounding is toward positive or negative infinity. In either case,
             the functions honor the sign of zero if floating-point arithmetic supports signed zeros.

    Footnote 344) An implementation may use the n-wchar sequence to determine extra information to be represented in
             the NaN’s significand.

    5    If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
         value resulting from the conversion is correctly rounded.

    6    In other than the "C" locale, additional locale-specific subject sequence forms may be
         accepted.

    7    If the subject sequence is empty or does not have the expected form, no conversion is
         performed; the value of nptr is stored in the object pointed to by endptr, provided
         that endptr is not a null pointer.
         Recommended practice

    8    If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
         the result is not exactly representable, the result should be one of the two numbers in the
         appropriate internal format that are adjacent to the hexadecimal floating source value,
         with the extra stipulation that the error should have a correct sign for the current rounding
         direction.

    9    If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
         <float.h>) significant digits, the result should be correctly rounded. If the subject
         sequence D has the decimal form and more than DECIMAL_DIG significant digits,
         consider the two bounding, adjacent decimal strings L and U, both having
         DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L ≤ D ≤ U.
         The result should be one of the (equal or adjacent) values that would be obtained by
         correctly rounding L and U according to the current rounding direction, with the extra
         stipulation that the error with respect to D should have a correct sign for the current
         rounding direction.[345]
         Returns

    Footnote 345) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
              to the same internal floating value, but if not will round to adjacent values.

    10   The functions return the converted value, if any. If no conversion could be performed,
         zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
         plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
         return type and sign of the value), and the value of the macro ERANGE is stored in
         errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
         no greater than the smallest normalized positive number in the return type; whether
         errno acquires the value ERANGE is implementation-defined.

### 7.29.4.1.2 [The wcstol, wcstoll, wcstoul, and wcstoull functions]

    1 Synopsis
              #include <wchar.h>
               long int wcstol(
                    const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr,
                    int base);
               long long int wcstoll(
                    const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr,
                    int base);
               unsigned long int wcstoul(
                    const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr,
                    int base);
               unsigned long long int wcstoull(
                    const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr,
                    int base);
        Description

    2   The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
        portion of the wide string pointed to by nptr to long int, long long int,
        unsigned long int, and unsigned long long int representation,
        respectively. First, they decompose the input string into three parts: an initial, possibly
        empty, sequence of white-space wide characters (as specified by the iswspace
        function), a subject sequence resembling an integer represented in some radix determined
        by the value of base, and a final wide string of one or more unrecognized wide
        characters, including the terminating null wide character of the input wide string. Then,
        they attempt to convert the subject sequence to an integer, and return the result.

    3   If the value of base is zero, the expected form of the subject sequence is that of an
        integer constant as described for the corresponding single-byte characters in 6.4.4.1,
        optionally preceded by a plus or minus sign, but not including an integer suffix. If the
        value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
        is a sequence of letters and digits representing an integer with the radix specified by
        base, optionally preceded by a plus or minus sign, but not including an integer suffix.
        The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
        letters and digits whose ascribed values are less than that of base are permitted. If the
        value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
        of letters and digits, following the sign if present.

    4   The subject sequence is defined as the longest initial subsequence of the input wide
        string, starting with the first non-white-space wide character, that is of the expected form.
        The subject sequence contains no wide characters if the input wide string is empty or
        consists entirely of white space, or if the first non-white-space wide character is other
        than a sign or a permissible letter or digit.

    5   If the subject sequence has the expected form and the value of base is zero, the sequence
        of wide characters starting with the first digit is interpreted as an integer constant
        according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
        value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
        letter its value as given above. If the subject sequence begins with a minus sign, the value
        resulting from the conversion is negated (in the return type). A pointer to the final wide
        string is stored in the object pointed to by endptr, provided that endptr is not a null
        pointer.

    6   In other than the "C" locale, additional locale-specific subject sequence forms may be
        accepted.

    7   If the subject sequence is empty or does not have the expected form, no conversion is
        performed; the value of nptr is stored in the object pointed to by endptr, provided
        that endptr is not a null pointer.
        Returns

    8   The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
        value, if any. If no conversion could be performed, zero is returned. If the correct value
        is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
        LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
        sign of the value, if any), and the value of the macro ERANGE is stored in errno.

### 7.29.4.2 [Wide string copying functions]

### 7.29.4.2.1 [The wcscpy function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcscpy(wchar_t * restrict s1,
                    const wchar_t * restrict s2);
        Description

    2   The wcscpy function copies the wide string pointed to by s2 (including the terminating
        null wide character) into the array pointed to by s1.
        Returns

    3   The wcscpy function returns the value of s1.

### 7.29.4.2.2 [The wcsncpy function]

    1 Synopsis
                #include <wchar.h>
                 wchar_t *wcsncpy(wchar_t * restrict s1,
                      const wchar_t * restrict s2,
                      size_t n);
        Description

    2   The wcsncpy function copies not more than n wide characters (those that follow a null
        wide character are not copied) from the array pointed to by s2 to the array pointed to by
        s1.[346]

    Footnote 346) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
             result will not be null-terminated.

    3   If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
        wide characters are appended to the copy in the array pointed to by s1, until n wide
        characters in all have been written.
        Returns

    4   The wcsncpy function returns the value of s1.

### 7.29.4.2.3 [The wmemcpy function]

    1 Synopsis
                #include <wchar.h>
                 wchar_t *wmemcpy(wchar_t * restrict s1,
                      const wchar_t * restrict s2,
                      size_t n);
        Description

    2   The wmemcpy function copies n wide characters from the object pointed to by s2 to the
        object pointed to by s1.
        Returns

    3   The wmemcpy function returns the value of s1.

### 7.29.4.2.4 [The wmemmove function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
                    size_t n);
        Description

    2   The wmemmove function copies n wide characters from the object pointed to by s2 to
        the object pointed to by s1. Copying takes place as if the n wide characters from the
        object pointed to by s2 are first copied into a temporary array of n wide characters that
        does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
        the temporary array are copied into the object pointed to by s1.
        Returns

    3   The wmemmove function returns the value of s1.

### 7.29.4.3 [Wide string concatenation functions]

### 7.29.4.3.1 [The wcscat function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcscat(wchar_t * restrict s1,
                    const wchar_t * restrict s2);
        Description

    2   The wcscat function appends a copy of the wide string pointed to by s2 (including the
        terminating null wide character) to the end of the wide string pointed to by s1. The initial
        wide character of s2 overwrites the null wide character at the end of s1.
        Returns

    3   The wcscat function returns the value of s1.

### 7.29.4.3.2 [The wcsncat function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcsncat(wchar_t * restrict s1,
                    const wchar_t * restrict s2,
                    size_t n);
        Description

    2   The wcsncat function appends not more than n wide characters (a null wide character
        and those that follow it are not appended) from the array pointed to by s2 to the end of
        the wide string pointed to by s1. The initial wide character of s2 overwrites the null
        wide character at the end of s1. A terminating null wide character is always appended to
        the result.[347]
        Returns

    Footnote 347) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
             wcslen(s1)+n+1.

    3   The wcsncat function returns the value of s1.

### 7.29.4.4 [Wide string comparison functions]

    1   Unless explicitly stated otherwise, the functions described in this subclause order two
        wide characters the same way as two integers of the underlying integer type designated
        by wchar_t.

### 7.29.4.4.1 [The wcscmp function]

    1 Synopsis
               #include <wchar.h>
                int wcscmp(const wchar_t *s1, const wchar_t *s2);
        Description

    2   The wcscmp function compares the wide string pointed to by s1 to the wide string
        pointed to by s2.
        Returns

    3   The wcscmp function returns an integer greater than, equal to, or less than zero,
        accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
        wide string pointed to by s2.

### 7.29.4.4.2 [The wcscoll function]

    1 Synopsis
               #include <wchar.h>
                int wcscoll(const wchar_t *s1, const wchar_t *s2);
        Description

    2   The wcscoll function compares the wide string pointed to by s1 to the wide string
        pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
        current locale.
        Returns

    3   The wcscoll function returns an integer greater than, equal to, or less than zero,
        accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
        wide string pointed to by s2 when both are interpreted as appropriate to the current
        locale.

### 7.29.4.4.3 [The wcsncmp function]

    1 Synopsis
              #include <wchar.h>
               int wcsncmp(const wchar_t *s1, const wchar_t *s2,
                    size_t n);
        Description

    2   The wcsncmp function compares not more than n wide characters (those that follow a
        null wide character are not compared) from the array pointed to by s1 to the array
        pointed to by s2.
        Returns

    3   The wcsncmp function returns an integer greater than, equal to, or less than zero,
        accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
        to, or less than the possibly null-terminated array pointed to by s2.

### 7.29.4.4.4 [The wcsxfrm function]

    1 Synopsis
              #include <wchar.h>
               size_t wcsxfrm(wchar_t * restrict s1,
                    const wchar_t * restrict s2,
                    size_t n);
        Description

    2   The wcsxfrm function transforms the wide string pointed to by s2 and places the
        resulting wide string into the array pointed to by s1. The transformation is such that if
        the wcscmp function is applied to two transformed wide strings, it returns a value greater
        than, equal to, or less than zero, corresponding to the result of the wcscoll function
        applied to the same two original wide strings. No more than n wide characters are placed
        into the resulting array pointed to by s1, including the terminating null wide character. If
        n is zero, s1 is permitted to be a null pointer.
        Returns

    3   The wcsxfrm function returns the length of the transformed wide string (not including
        the terminating null wide character). If the value returned is n or greater, the contents of
        the array pointed to by s1 are indeterminate.

    4   EXAMPLE The value of the following expression is the length of the array needed to hold the
        transformation of the wide string pointed to by s:
               1 + wcsxfrm(NULL, s, 0)

### 7.29.4.4.5 [The wmemcmp function]

    1 Synopsis
              #include <wchar.h>
               int wmemcmp(const wchar_t *s1, const wchar_t *s2,
                    size_t n);
        Description

    2   The wmemcmp function compares the first n wide characters of the object pointed to by
        s1 to the first n wide characters of the object pointed to by s2.
        Returns

    3   The wmemcmp function returns an integer greater than, equal to, or less than zero,
        accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
        pointed to by s2.

### 7.29.4.5 [Wide string search functions]

### 7.29.4.5.1 [The wcschr function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcschr(const wchar_t *s, wchar_t c);
        Description

    2   The wcschr function locates the first occurrence of c in the wide string pointed to by s.
        The terminating null wide character is considered to be part of the wide string.
        Returns

    3   The wcschr function returns a pointer to the located wide character, or a null pointer if
        the wide character does not occur in the wide string.

### 7.29.4.5.2 [The wcscspn function]

    1 Synopsis
              #include <wchar.h>
               size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
        Description

    2   The wcscspn function computes the length of the maximum initial segment of the wide
        string pointed to by s1 which consists entirely of wide characters not from the wide
        string pointed to by s2.
        Returns

    3   The wcscspn function returns the length of the segment.

### 7.29.4.5.3 [The wcspbrk function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
        Description

    2   The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
        any wide character from the wide string pointed to by s2.
        Returns

    3   The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
        no wide character from s2 occurs in s1.

### 7.29.4.5.4 [The wcsrchr function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
        Description

    2   The wcsrchr function locates the last occurrence of c in the wide string pointed to by
        s. The terminating null wide character is considered to be part of the wide string.
        Returns

    3   The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
        not occur in the wide string.

### 7.29.4.5.5 [The wcsspn function]

    1 Synopsis
              #include <wchar.h>
               size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
        Description

    2   The wcsspn function computes the length of the maximum initial segment of the wide
        string pointed to by s1 which consists entirely of wide characters from the wide string
        pointed to by s2.
        Returns

    3   The wcsspn function returns the length of the segment.

### 7.29.4.5.6 [The wcsstr function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
        Description

    2   The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
        the sequence of wide characters (excluding the terminating null wide character) in the
        wide string pointed to by s2.
        Returns

    3   The wcsstr function returns a pointer to the located wide string, or a null pointer if the
        wide string is not found. If s2 points to a wide string with zero length, the function
        returns s1.

### 7.29.4.5.7 [The wcstok function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wcstok(wchar_t * restrict s1,
                    const wchar_t * restrict s2,
                    wchar_t ** restrict ptr);
        Description

    2   A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
        a sequence of tokens, each of which is delimited by a wide character from the wide string
        pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
        which the wcstok function stores information necessary for it to continue scanning the
        same wide string.

    3   The first call in a sequence has a non-null first argument and stores an initial value in the
        object pointed to by ptr. Subsequent calls in the sequence have a null first argument and
        the object pointed to by ptr is required to have the value stored by the previous call in
        the sequence, which is then updated. The separator wide string pointed to by s2 may be
        different from call to call.

    4   The first call in the sequence searches the wide string pointed to by s1 for the first wide
        character that is not contained in the current separator wide string pointed to by s2. If no
        such wide character is found, then there are no tokens in the wide string pointed to by s1
        and the wcstok function returns a null pointer. If such a wide character is found, it is
        the start of the first token.

    5   The wcstok function then searches from there for a wide character that is contained in
        the current separator wide string. If no such wide character is found, the current token
        extends to the end of the wide string pointed to by s1, and subsequent searches in the
        same wide string for a token return a null pointer. If such a wide character is found, it is
        overwritten by a null wide character, which terminates the current token.

    6   In all cases, the wcstok function stores sufficient information in the pointer pointed to
        by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
        value for ptr, shall start searching just past the element overwritten by a null wide
        character (if any).
        Returns

    7   The wcstok function returns a pointer to the first wide character of a token, or a null
        pointer if there is no token.

    8   EXAMPLE
               #include <wchar.h>
               static wchar_t str1[] = L"?a???b,,,#c";
               static wchar_t str2[] = L"\t \t";
               wchar_t *t, *ptr1, *ptr2;
               t = wcstok(str1, L"?", &ptr1);                // t points to the token L"a"
               t = wcstok(NULL, L",", &ptr1);                // t points to the token L"??b"
               t = wcstok(str2, L" \t", &ptr2);              // t is a null pointer
               t = wcstok(NULL, L"#,", &ptr1);               // t points to the token L"c"
               t = wcstok(NULL, L"?", &ptr1);                // t is a null pointer

### 7.29.4.5.8 [The wmemchr function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wmemchr(const wchar_t *s, wchar_t c,
                    size_t n);
        Description

    2   The wmemchr function locates the first occurrence of c in the initial n wide characters of
        the object pointed to by s.
        Returns

    3   The wmemchr function returns a pointer to the located wide character, or a null pointer if
        the wide character does not occur in the object.

### 7.29.4.6 [Miscellaneous functions]

### 7.29.4.6.1 [The wcslen function]

    1 Synopsis
              #include <wchar.h>
               size_t wcslen(const wchar_t *s);
        Description

    2   The wcslen function computes the length of the wide string pointed to by s.
        Returns

    3   The wcslen function returns the number of wide characters that precede the terminating
        null wide character.

### 7.29.4.6.2 [The wmemset function]

    1 Synopsis
              #include <wchar.h>
               wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
        Description

    2   The wmemset function copies the value of c into each of the first n wide characters of
        the object pointed to by s.
        Returns

    3   The wmemset function returns the value of s.

### 7.29.5 [Wide character time conversion functions]

### 7.29.5.1 [The wcsftime function]

    1 Synopsis
              #include <time.h>
               #include <wchar.h>
               size_t wcsftime(wchar_t * restrict s,
                    size_t maxsize,
                    const wchar_t * restrict format,
                    const struct tm * restrict timeptr);
        Description

    2   The wcsftime function is equivalent to the strftime function, except that:
        — The argument s points to the initial element of an array of wide characters into which
          the generated output is to be placed.
        — The argument maxsize indicates the limiting number of wide characters.
        — The argument format is a wide string and the conversion specifiers are replaced by
          corresponding sequences of wide characters.
        — The return value indicates the number of wide characters.
        Returns

    3   If the total number of resulting wide characters including the terminating null wide
        character is not more than maxsize, the wcsftime function returns the number of
        wide characters placed into the array pointed to by s not including the terminating null
        wide character. Otherwise, zero is returned and the contents of the array are
        indeterminate.

### 7.29.6 [Extended multibyte/wide character conversion utilities]

    1   The header <wchar.h> declares an extended set of functions useful for conversion
        between multibyte characters and wide characters.

    2   Most of the following functions — those that are listed as ‘‘restartable’’, 7.29.6.3 and
        7.29.6.4 — take as a last argument a pointer to an object of type mbstate_t that is used
        to describe the current conversion state from a particular multibyte character sequence to
        a wide character sequence (or the reverse) under the rules of a particular setting for the
        LC_CTYPE category of the current locale.

    3   The initial conversion state corresponds, for a conversion in either direction, to the
        beginning of a new multibyte character in the initial shift state. A zero-valued
        mbstate_t object is (at least) one way to describe an initial conversion state. A zero-
        valued mbstate_t object can be used to initiate conversion involving any multibyte
        character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
        been altered by any of the functions described in this subclause, and is then used with a
        different multibyte character sequence, or in the other conversion direction, or with a
        different LC_CTYPE category setting than on earlier function calls, the behavior is
        undefined.[348]

    Footnote 348) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and
             mbsrtowcs functions as long as they are used to step sequentially through the same multibyte
             character string.

    4   On entry, each function takes the described conversion state (either internal or pointed to
        by an argument) as current. The conversion state described by the referenced object is
        altered as needed to track the shift state, and the position within a multibyte character, for
        the associated multibyte character sequence.

### 7.29.6.1 [Single-byte/wide character conversion functions]

### 7.29.6.1.1 [The btowc function]

    1 Synopsis
              #include <wchar.h>
               wint_t btowc(int c);
        Description

    2   The btowc function determines whether c constitutes a valid single-byte character in the
        initial shift state.
        Returns

    3   The btowc function returns WEOF if c has the value EOF or if (unsigned char)c
        does not constitute a valid single-byte character in the initial shift state. Otherwise, it
        returns the wide character representation of that character.

### 7.29.6.1.2 [The wctob function]

    1 Synopsis
              #include <wchar.h>
               int wctob(wint_t c);
        Description

    2   The wctob function determines whether c corresponds to a member of the extended
        character set whose multibyte character representation is a single byte when in the initial
        shift state.
        Returns

    3   The wctob function returns EOF if c does not correspond to a multibyte character with
        length one in the initial shift state. Otherwise, it returns the single-byte representation of
        that character as an unsigned char converted to an int.

### 7.29.6.2 [Conversion state functions]

### 7.29.6.2.1 [The mbsinit function]

    1 Synopsis
              #include <wchar.h>
               int mbsinit(const mbstate_t *ps);
        Description

    2   If ps is not a null pointer, the mbsinit function determines whether the referenced
        mbstate_t object describes an initial conversion state.
        Returns

    3   The mbsinit function returns nonzero if ps is a null pointer or if the referenced object
        describes an initial conversion state; otherwise, it returns zero.

### 7.29.6.3 [Restartable multibyte/wide character conversion functions]

    1   These functions differ from the corresponding multibyte character functions of 7.22.7
        (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type
        pointer to mbstate_t that points to an object that can completely describe the current
        conversion state of the associated multibyte character sequence. If ps is a null pointer,
        each function uses its own internal mbstate_t object instead, which is initialized at
        program startup to the initial conversion state; the functions are not required to avoid data
        races with other calls to the same function in this case. The implementation behaves as if
        no library function calls these functions with a null pointer for ps.

    2   Also unlike their corresponding functions, the return value does not represent whether the
        encoding is state-dependent.

### 7.29.6.3.1 [The mbrlen function]

    1 Synopsis
              #include <wchar.h>
               size_t mbrlen(const char * restrict s,
                    size_t n,
                    mbstate_t * restrict ps);
        Description

    2   The mbrlen function is equivalent to the call:
               mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
        where internal is the mbstate_t object for the mbrlen function, except that the
        expression designated by ps is evaluated only once.
        Returns

    3   The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
        or (size_t)(-1).
        Forward references: the mbrtowc function (7.29.6.3.2).

### 7.29.6.3.2 [The mbrtowc function]

    1 Synopsis
               #include <wchar.h>
                size_t mbrtowc(wchar_t * restrict pwc,
                     const char * restrict s,
                     size_t n,
                     mbstate_t * restrict ps);
        Description

    2   If s is a null pointer, the mbrtowc function is equivalent to the call:
                        mbrtowc(NULL, "", 1, ps)
        In this case, the values of the parameters pwc and n are ignored.

    3   If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with
        the byte pointed to by s to determine the number of bytes needed to complete the next
        multibyte character (including any shift sequences). If the function determines that the
        next multibyte character is complete and valid, it determines the value of the
        corresponding wide character and then, if pwc is not a null pointer, stores that value in
        the object pointed to by pwc. If the corresponding wide character is the null wide
        character, the resulting state described is the initial conversion state.
        Returns

    4   The mbrtowc function returns the first of the following that applies (given the current
        conversion state):
        0                     if the next n or fewer bytes complete the multibyte character that
                              corresponds to the null wide character (which is the value stored).
        between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                           character (which is the value stored); the value returned is the number
                           of bytes that complete the multibyte character.
        (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                     multibyte character, and all n bytes have been processed (no value is
                     stored).[349]
        (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                     do not contribute to a complete and valid multibyte character (no
                     value is stored); the value of the macro EILSEQ is stored in errno,
                     and the conversion state is unspecified.

    Footnote 349) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
             sequence of redundant shift sequences (for implementations with state-dependent encodings).

### 7.29.6.3.3 [The wcrtomb function]

    1 Synopsis
               #include <wchar.h>
                size_t wcrtomb(char * restrict s,
                     wchar_t wc,
                     mbstate_t * restrict ps);
        Description

    2   If s is a null pointer, the wcrtomb function is equivalent to the call
                        wcrtomb(buf, L'\0', ps)
        where buf is an internal buffer.

    3   If s is not a null pointer, the wcrtomb function determines the number of bytes needed
        to represent the multibyte character that corresponds to the wide character given by wc
        (including any shift sequences), and stores the multibyte character representation in the
        array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
        wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
        to restore the initial shift state; the resulting state described is the initial conversion state.
        Returns

    4   The wcrtomb function returns the number of bytes stored in the array object (including
        any shift sequences). When wc is not a valid wide character, an encoding error occurs:
        the function stores the value of the macro EILSEQ in errno and returns
        (size_t)(-1); the conversion state is unspecified.

### 7.29.6.4 [Restartable multibyte/wide string conversion functions]

    1   These functions differ from the corresponding multibyte string functions of 7.22.8
        (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to
        mbstate_t that points to an object that can completely describe the current conversion
        state of the associated multibyte character sequence. If ps is a null pointer, each function
        uses its own internal mbstate_t object instead, which is initialized at program startup
        to the initial conversion state; the functions are not required to avoid data races with other
        calls to the same function in this case. The implementation behaves as if no library
        function calls these functions with a null pointer for ps.

    2   Also unlike their corresponding functions, the conversion source parameter, src, has a
        pointer-to-pointer type. When the function is storing the results of conversions (that is,
        when dst is not a null pointer), the pointer object pointed to by this parameter is updated
        to reflect the amount of the source processed by that invocation.

### 7.29.6.4.1 [The mbsrtowcs function]

    1 Synopsis
                #include <wchar.h>
                 size_t mbsrtowcs(wchar_t * restrict dst,
                      const char ** restrict src,
                      size_t len,
                      mbstate_t * restrict ps);
        Description

    2   The mbsrtowcs function converts a sequence of multibyte characters that begins in the
        conversion state described by the object pointed to by ps, from the array indirectly
        pointed to by src into a sequence of corresponding wide characters. If dst is not a null
        pointer, the converted characters are stored into the array pointed to by dst. Conversion
        continues up to and including a terminating null character, which is also stored.
        Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
        not form a valid multibyte character, or (if dst is not a null pointer) when len wide
        characters have been stored into the array pointed to by dst.[350] Each conversion takes
        place as if by a call to the mbrtowc function.

    Footnote 350) Thus, the value of len is ignored if dst is a null pointer.

    3   If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
        pointer (if conversion stopped due to reaching a terminating null character) or the address
        just past the last multibyte character converted (if any). If conversion stopped due to
        reaching a terminating null character and if dst is not a null pointer, the resulting state
        described is the initial conversion state.
        Returns

    4   If the input conversion encounters a sequence of bytes that do not form a valid multibyte
        character, an encoding error occurs: the mbsrtowcs function stores the value of the
        macro EILSEQ in errno and returns (size_t)(-1); the conversion state is
        unspecified. Otherwise, it returns the number of multibyte characters successfully
        converted, not including the terminating null character (if any).

### 7.29.6.4.2 [The wcsrtombs function]

    1 Synopsis
               #include <wchar.h>
                size_t wcsrtombs(char * restrict dst,
                     const wchar_t ** restrict src,
                     size_t len,
                     mbstate_t * restrict ps);
        Description

    2   The wcsrtombs function converts a sequence of wide characters from the array
        indirectly pointed to by src into a sequence of corresponding multibyte characters that
        begins in the conversion state described by the object pointed to by ps. If dst is not a
        null pointer, the converted characters are then stored into the array pointed to by dst.
        Conversion continues up to and including a terminating null wide character, which is also
        stored. Conversion stops earlier in two cases: when a wide character is reached that does
        not correspond to a valid multibyte character, or (if dst is not a null pointer) when the
        next multibyte character would exceed the limit of len total bytes to be stored into the
        array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
        function.[351]

    Footnote 351) If conversion stops because a terminating null wide character has been reached, the bytes stored
             include those necessary to reach the initial shift state immediately before the null byte.

    3   If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
        pointer (if conversion stopped due to reaching a terminating null wide character) or the
        address just past the last wide character converted (if any). If conversion stopped due to
        reaching a terminating null wide character, the resulting state described is the initial
        conversion state.
        Returns

    4   If conversion stops because a wide character is reached that does not correspond to a
        valid multibyte character, an encoding error occurs: the wcsrtombs function stores the
        value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
        state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
        character sequence, not including the terminating null character (if any).

### 7.30 [Wide character classification and mapping utilities <wctype.h>]

### 7.30.1 [Introduction]

    1   The header <wctype.h> defines one macro, and declares three data types and many
        functions.[352]

    Footnote 352) See ‘‘future library directions’’ (7.31.17).

    2   The types declared are
                 wint_t
        described in 7.29.1;
                 wctrans_t
        which is a scalar type that can hold values which represent locale-specific character
        mappings; and
                 wctype_t
        which is a scalar type that can hold values which represent locale-specific character
        classifications.

    3   The macro defined is WEOF (described in 7.29.1).

    4   The functions declared are grouped as follows:
        — Functions that provide wide character classification;
        — Extensible functions that provide wide character classification;
        — Functions that provide wide character case mapping;
        — Extensible functions that provide wide character mapping.

    5   For all functions described in this subclause that accept an argument of type wint_t, the
        value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
        this argument has any other value, the behavior is undefined.

    6   The behavior of these functions is affected by the LC_CTYPE category of the current
        locale.

### 7.30.2 [Wide character classification utilities]

    1   The header <wctype.h> declares several functions useful for classifying wide
        characters.

    2   The term printing wide character refers to a member of a locale-specific set of wide
        characters, each of which occupies at least one printing position on a display device. The
        term control wide character refers to a member of a locale-specific set of wide characters
        that are not printing wide characters.

### 7.30.2.1 [Wide character classification functions]

    1   The functions in this subclause return nonzero (true) if and only if the value of the
        argument wc conforms to that in the description of the function.

    2   Each of the following functions returns true for each wide character that corresponds (as
        if by a call to the wctob function) to a single-byte character for which the corresponding
        character classification function from 7.4.1 returns true, except that the iswgraph and
        iswpunct functions may differ with respect to wide characters other than L' ' that are
        both printing and white-space wide characters.[353]
        Forward references: the wctob function (7.29.6.1.2).

    Footnote 353) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
             iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
             (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)
             && iswspace(wc) is true, but not both.

### 7.30.2.1.1 [The iswalnum function]

    1 Synopsis
               #include <wctype.h>
                int iswalnum(wint_t wc);
        Description

    2   The iswalnum function tests for any wide character for which iswalpha or
        iswdigit is true.

### 7.30.2.1.2 [The iswalpha function]

    1 Synopsis
               #include <wctype.h>
                int iswalpha(wint_t wc);
        Description

    2   The iswalpha function tests for any wide character for which iswupper or
        iswlower is true, or any wide character that is one of a locale-specific set of alphabetic
        wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace
        is true.[354]

    Footnote 354) The functions iswlower and iswupper test true or false separately for each of these additional
             wide characters; all four combinations are possible.

### 7.30.2.1.3 [The iswblank function]

    1 Synopsis
               #include <wctype.h>
                int iswblank(wint_t wc);
        Description

    2   The iswblank function tests for any wide character that is a standard blank wide
        character or is one of a locale-specific set of wide characters for which iswspace is true
        and that is used to separate words within a line of text. The standard blank wide
        characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
        locale, iswblank returns true only for the standard blank characters.

### 7.30.2.1.4 [The iswcntrl function]

    1 Synopsis
               #include <wctype.h>
                int iswcntrl(wint_t wc);
        Description

    2   The iswcntrl function tests for any control wide character.

### 7.30.2.1.5 [The iswdigit function]

    1 Synopsis
               #include <wctype.h>
                int iswdigit(wint_t wc);
        Description

    2   The iswdigit function tests for any wide character that corresponds to a decimal-digit
        character (as defined in 5.2.1).

### 7.30.2.1.6 [The iswgraph function]

    1 Synopsis
               #include <wctype.h>
                int iswgraph(wint_t wc);
        Description

    2   The iswgraph function tests for any wide character for which iswprint is true and
        iswspace is false.[355]

    Footnote 355) Note that the behavior of the iswgraph and iswpunct functions may differ from their
             corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
             characters other than ' '.

### 7.30.2.1.7 [The iswlower function]

    1 Synopsis
               #include <wctype.h>
                int iswlower(wint_t wc);
        Description

    2   The iswlower function tests for any wide character that corresponds to a lowercase
        letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
        iswdigit, iswpunct, or iswspace is true.

### 7.30.2.1.8 [The iswprint function]

    1 Synopsis
               #include <wctype.h>
                int iswprint(wint_t wc);
        Description

    2   The iswprint function tests for any printing wide character.

### 7.30.2.1.9 [The iswpunct function]

    1 Synopsis
               #include <wctype.h>
                int iswpunct(wint_t wc);
        Description

    2   The iswpunct function tests for any printing wide character that is one of a locale-
        specific set of punctuation wide characters for which neither iswspace nor iswalnum
        is true.[355]

    Footnote 355) Note that the behavior of the iswgraph and iswpunct functions may differ from their
             corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
             characters other than ' '.

### 7.30.2.1.10 [The iswspace function]

    1 Synopsis
               #include <wctype.h>
                int iswspace(wint_t wc);
        Description

    2   The iswspace function tests for any wide character that corresponds to a locale-specific
        set of white-space wide characters for which none of iswalnum, iswgraph, or
        iswpunct is true.

### 7.30.2.1.11 [The iswupper function]

    1 Synopsis
              #include <wctype.h>
               int iswupper(wint_t wc);
        Description

    2   The iswupper function tests for any wide character that corresponds to an uppercase
        letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
        iswdigit, iswpunct, or iswspace is true.

### 7.30.2.1.12 [The iswxdigit function]

    1 Synopsis
              #include <wctype.h>
               int iswxdigit(wint_t wc);
        Description

    2   The iswxdigit function tests for any wide character that corresponds to a
        hexadecimal-digit character (as defined in 6.4.4.1).

### 7.30.2.2 [Extensible wide character classification functions]

    1   The functions wctype and iswctype provide extensible wide character classification
        as well as testing equivalent to that performed by the functions described in the previous
        subclause (7.30.2.1).

### 7.30.2.2.1 [The iswctype function]

    1 Synopsis
              #include <wctype.h>
               int iswctype(wint_t wc, wctype_t desc);
        Description

    2   The iswctype function determines whether the wide character wc has the property
        described by desc. The current setting of the LC_CTYPE category shall be the same as
        during the call to wctype that returned the value desc.

    3   Each of the following expressions has a truth-value equivalent to the call to the wide
        character classification function (7.30.2.1) in the comment that follows the expression:
               iswctype(wc, wctype("alnum"))                    // iswalnum(wc)
               iswctype(wc, wctype("alpha"))                    // iswalpha(wc)
               iswctype(wc, wctype("blank"))                    // iswblank(wc)
               iswctype(wc, wctype("cntrl"))                    // iswcntrl(wc)
               iswctype(wc, wctype("digit"))                    // iswdigit(wc)
               iswctype(wc, wctype("graph"))                    // iswgraph(wc)
               iswctype(wc, wctype("lower"))                    // iswlower(wc)
               iswctype(wc, wctype("print"))                    // iswprint(wc)
               iswctype(wc, wctype("punct"))                    // iswpunct(wc)
               iswctype(wc, wctype("space"))                    // iswspace(wc)
               iswctype(wc, wctype("upper"))                    // iswupper(wc)
               iswctype(wc, wctype("xdigit"))                   // iswxdigit(wc)
        Returns

    4   The iswctype function returns nonzero (true) if and only if the value of the wide
        character wc has the property described by desc. If desc is zero, the iswctype
        function returns zero (false).
        Forward references: the wctype function (7.30.2.2.2).

### 7.30.2.2.2 [The wctype function]

    1 Synopsis
              #include <wctype.h>
               wctype_t wctype(const char *property);
        Description

    2   The wctype function constructs a value with type wctype_t that describes a class of
        wide characters identified by the string argument property.

    3   The strings listed in the description of the iswctype function shall be valid in all
        locales as property arguments to the wctype function.
        Returns

    4   If property identifies a valid class of wide characters according to the LC_CTYPE
        category of the current locale, the wctype function returns a nonzero value that is valid
        as the second argument to the iswctype function; otherwise, it returns zero.

### 7.30.3 [Wide character case mapping utilities]

    1   The header <wctype.h> declares several functions useful for mapping wide characters.

### 7.30.3.1 [Wide character case mapping functions]

### 7.30.3.1.1 [The towlower function]

    1 Synopsis
              #include <wctype.h>
               wint_t towlower(wint_t wc);
        Description

    2   The towlower function converts an uppercase letter to a corresponding lowercase letter.
        Returns

    3   If the argument is a wide character for which iswupper is true and there are one or
        more corresponding wide characters, as specified by the current locale, for which
        iswlower is true, the towlower function returns one of the corresponding wide
        characters (always the same one for any given locale); otherwise, the argument is
        returned unchanged.

### 7.30.3.1.2 [The towupper function]

    1 Synopsis
              #include <wctype.h>
               wint_t towupper(wint_t wc);
        Description

    2   The towupper function converts a lowercase letter to a corresponding uppercase letter.
        Returns

    3   If the argument is a wide character for which iswlower is true and there are one or
        more corresponding wide characters, as specified by the current locale, for which
        iswupper is true, the towupper function returns one of the corresponding wide
        characters (always the same one for any given locale); otherwise, the argument is
        returned unchanged.

### 7.30.3.2 [Extensible wide character case mapping functions]

    1   The functions wctrans and towctrans provide extensible wide character mapping as
        well as case mapping equivalent to that performed by the functions described in the
        previous subclause (7.30.3.1).

### 7.30.3.2.1 [The towctrans function]

    1 Synopsis
              #include <wctype.h>
               wint_t towctrans(wint_t wc, wctrans_t desc);
        Description

    2   The towctrans function maps the wide character wc using the mapping described by
        desc. The current setting of the LC_CTYPE category shall be the same as during the call
        to wctrans that returned the value desc.

    3   Each of the following expressions behaves the same as the call to the wide character case
        mapping function (7.30.3.1) in the comment that follows the expression:
               towctrans(wc, wctrans("tolower"))                      // towlower(wc)
               towctrans(wc, wctrans("toupper"))                      // towupper(wc)
        Returns

    4   The towctrans function returns the mapped value of wc using the mapping described
        by desc. If desc is zero, the towctrans function returns the value of wc.

### 7.30.3.2.2 [The wctrans function]

    1 Synopsis
              #include <wctype.h>
               wctrans_t wctrans(const char *property);
        Description

    2   The wctrans function constructs a value with type wctrans_t that describes a
        mapping between wide characters identified by the string argument property.

    3   The strings listed in the description of the towctrans function shall be valid in all
        locales as property arguments to the wctrans function.
        Returns

    4   If property identifies a valid mapping of wide characters according to the LC_CTYPE
        category of the current locale, the wctrans function returns a nonzero value that is valid
        as the second argument to the towctrans function; otherwise, it returns zero.

### 7.31 [Future library directions]

    1   The following names are grouped under individual headers for convenience. All external
        names described below are reserved no matter what headers are included by the program.

### 7.31.1 [Complex arithmetic <complex.h>]

    1   The function names
             cerf                cexpm1              clog2
             cerfc               clog10              clgamma
             cexp2               clog1p              ctgamma
        and the same names suffixed with f or l may be added to the declarations in the
        <complex.h> header.

### 7.31.2 [Character handling <ctype.h>]

    1   Function names that begin with either is or to, and a lowercase letter may be added to
        the declarations in the <ctype.h> header.

### 7.31.3 [Errors <errno.h>]

    1   Macros that begin with E and a digit or E and an uppercase letter may be added to the
        macros defined in the <errno.h> header.

### 7.31.4 [Floating-point environment <fenv.h>]

    1   Macros that begin with FE_ and an uppercase letter may be added to the macros defined
        in the <fenv.h> header.

### 7.31.5 [Format conversion of integer types <inttypes.h>]

    1   Macros that begin with either PRI or SCN, and either a lowercase letter or X may be
        added to the macros defined in the <inttypes.h> header.

### 7.31.6 [Localization <locale.h>]

    1   Macros that begin with LC_ and an uppercase letter may be added to the macros defined
        in the <locale.h> header.

### 7.31.7 [Signal handling <signal.h>]

    1   Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
        letter may be added to the macros defined in the <signal.h> header.

### 7.31.8 [Atomics <stdatomic.h>]

    1   Macros that begin with ATOMIC_ and an uppercase letter may be added to the macros
        defined in the <stdatomic.h> header. Typedef names that begin with either
        atomic_ or memory_, and a lowercase letter may be added to the declarations in the
        <stdatomic.h> header. Enumeration constants that begin with memory_order_
        and a lowercase letter may be added to the definition of the memory_order type in the
        <stdatomic.h> header. Function names that begin with atomic_ and a lowercase
        letter may be added to the declarations in the <stdatomic.h> header.

### 7.31.9 [Boolean type and values <stdbool.h>]

    1   The ability to undefine and perhaps then redefine the macros bool, true, and false is
        an obsolescent feature.

### 7.31.10 [Integer types <stdint.h>]

    1   Typedef names beginning with int or uint and ending with _t may be added to the
        types defined in the <stdint.h> header. Macro names beginning with INT or UINT
        and ending with _MAX, _MIN, or _C may be added to the macros defined in the
        <stdint.h> header.

### 7.31.11 [Input/output <stdio.h>]

    1   Lowercase letters may be added to the conversion specifiers and length modifiers in
        fprintf and fscanf. Other characters may be used in extensions.

    2   The use of ungetc on a binary stream where the file position indicator is zero prior to
        the call is an obsolescent feature.

### 7.31.12 [General utilities <stdlib.h>]

    1   Function names that begin with str and a lowercase letter may be added to the
        declarations in the <stdlib.h> header.

### 7.31.13 [String handling <string.h>]

    1   Function names that begin with str, mem, or wcs and a lowercase letter may be added
        to the declarations in the <string.h> header.

### 7.31.14 [Date and time <time.h>]

    Macros beginning with TIME_ and an uppercase letter may be added to the macros in the
        <time.h> header.

### 7.31.15 [Threads <threads.h>]

    1   Function names, type names, and enumeration constants that begin with either cnd_,
        mtx_, thrd_, or tss_, and a lowercase letter may be added to the declarations in the
        <threads.h> header.

### 7.31.16 [Extended multibyte and wide character utilities <wchar.h>]

    1   Function names that begin with wcs and a lowercase letter may be added to the
        declarations in the <wchar.h> header.

    2   Lowercase letters may be added to the conversion specifiers and length modifiers in

### 7.31.17 [Wide character classification and mapping utilities]

    1 <wctype.h>
       Function names that begin with is or to and a lowercase letter may be added to the
        declarations in the <wctype.h> header.

### A. [Annex A (informative) Language syntax summary]

    1   NOTE   The notation is described in 6.1.

### A.1 [Lexical grammar]

### A.1.1 [Lexical elements]

    (6.4) token:
                       keyword
                       identifier
                       constant
                       string-literal
                       punctuator
        (6.4) preprocessing-token:
                      header-name
                      identifier
                      pp-number
                      character-constant
                      string-literal
                      punctuator
                      each non-white-space character that cannot be one of the above

### A.1.2 [Keywords]

    (6.4.1) keyword: one of
                  auto                    ∗ if                       unsigned
                  break                     inline                   void
                  case                      int                      volatile
                  char                      long                     while
                  const                     register                 _Alignas
                  continue                  restrict                 _Alignof
                  default                   return                   _Atomic
                  do                        short                    _Bool
                  double                    signed                   _Complex
                  else                      sizeof                   _Generic
                  enum                      static                   _Imaginary
                  extern                    struct                   _Noreturn
                  float                     switch                   _Static_assert
                  for                       typedef                  _Thread_local
                  goto                      union

### A.1.3 [Identifiers]

    (6.4.2.1) identifier:
                   identifier-nondigit
                   identifier identifier-nondigit
                   identifier digit
    (6.4.2.1) identifier-nondigit:
                   nondigit
                   universal-character-name
                   other implementation-defined characters
    (6.4.2.1) nondigit: one of
                  _ a b c             d   e    f    g   h    i   j   k   l   m
                       n o p          q   r    s    t   u    v   w   x   y   z
                       A B C          D   E    F    G   H    I   J   K   L   M
                       N O P          Q   R    S    T   U    V   W   X   Y   Z
    (6.4.2.1) digit: one of
                   0 1 2         3    4   5    6    7   8    9

### A.1.4 [Universal character names]

    (6.4.3) universal-character-name:
                  \u hex-quad
                  \U hex-quad hex-quad
    (6.4.3) hex-quad:
                  hexadecimal-digit hexadecimal-digit
                               hexadecimal-digit hexadecimal-digit

### A.1.5 [Constants]

    (6.4.4) constant:
                  integer-constant
                  floating-constant
                  enumeration-constant
                  character-constant
    (6.4.4.1) integer-constant:
                   decimal-constant integer-suffixopt
                   octal-constant integer-suffixopt
                   hexadecimal-constant integer-suffixopt
    (6.4.4.1) decimal-constant:
                  nonzero-digit
                  decimal-constant digit
    (6.4.4.1) octal-constant:
                   0
                   octal-constant octal-digit
    (6.4.4.1) hexadecimal-constant:
                  hexadecimal-prefix hexadecimal-digit
                  hexadecimal-constant hexadecimal-digit
    (6.4.4.1) hexadecimal-prefix: one of
                  0x 0X
    (6.4.4.1) nonzero-digit: one of
                  1 2 3 4 5              6      7   8   9
    (6.4.4.1) octal-digit: one of
                   0 1 2 3          4    5      6   7
    (6.4.4.1) hexadecimal-digit: one of
                  0 1 2 3 4 5                6      7    8   9
                  a b c d e f
                  A B C D E F
    (6.4.4.1) integer-suffix:
                   unsigned-suffix long-suffixopt
                   unsigned-suffix long-long-suffix
                   long-suffix unsigned-suffixopt
                   long-long-suffix unsigned-suffixopt
    (6.4.4.1) unsigned-suffix: one of
                   u U
    (6.4.4.1) long-suffix: one of
                   l L
    (6.4.4.1) long-long-suffix: one of
                   ll LL
    (6.4.4.2) floating-constant:
                    decimal-floating-constant
                    hexadecimal-floating-constant
    (6.4.4.2) decimal-floating-constant:
                  fractional-constant exponent-partopt floating-suffixopt
                  digit-sequence exponent-part floating-suffixopt
    (6.4.4.2) hexadecimal-floating-constant:
                  hexadecimal-prefix hexadecimal-fractional-constant
                                 binary-exponent-part floating-suffixopt
                  hexadecimal-prefix hexadecimal-digit-sequence
                                 binary-exponent-part floating-suffixopt
    (6.4.4.2) fractional-constant:
                   digit-sequenceopt . digit-sequence
                   digit-sequence .
    (6.4.4.2) exponent-part:
                  e signopt digit-sequence
                  E signopt digit-sequence
    (6.4.4.2) sign: one of
                   + -
    (6.4.4.2) digit-sequence:
                   digit
                   digit-sequence digit
    (6.4.4.2) hexadecimal-fractional-constant:
                  hexadecimal-digit-sequenceopt .
                                 hexadecimal-digit-sequence
                  hexadecimal-digit-sequence .
    (6.4.4.2) binary-exponent-part:
                   p signopt digit-sequence
                   P signopt digit-sequence
    (6.4.4.2) hexadecimal-digit-sequence:
                  hexadecimal-digit
                  hexadecimal-digit-sequence hexadecimal-digit
    (6.4.4.2) floating-suffix: one of
                    f l F L
    (6.4.4.3) enumeration-constant:
                  identifier
    (6.4.4.4) character-constant:
                  ' c-char-sequence '
                  L' c-char-sequence '
                  u' c-char-sequence '
                  U' c-char-sequence '
    (6.4.4.4) c-char-sequence:
                   c-char
                   c-char-sequence c-char
    (6.4.4.4) c-char:
                   any member of the source character set except
                                the single-quote ', backslash \, or new-line character
                   escape-sequence
    (6.4.4.4) escape-sequence:
                  simple-escape-sequence
                  octal-escape-sequence
                  hexadecimal-escape-sequence
                  universal-character-name
    (6.4.4.4) simple-escape-sequence: one of
                  \' \" \? \\
                  \a \b \f \n \r \t                   \v
    (6.4.4.4) octal-escape-sequence:
                   \ octal-digit
                   \ octal-digit octal-digit
                   \ octal-digit octal-digit octal-digit
    (6.4.4.4) hexadecimal-escape-sequence:
                  \x hexadecimal-digit
                  hexadecimal-escape-sequence hexadecimal-digit

### A.1.6 [String literals]

    (6.4.5) string-literal:
                   encoding-prefixopt " s-char-sequenceopt "
    (6.4.5) encoding-prefix:
                  u8
                  u
                  U
                  L
    (6.4.5) s-char-sequence:
                   s-char
                   s-char-sequence s-char
    (6.4.5) s-char:
                   any member of the source character set except
                                the double-quote ", backslash \, or new-line character
                   escape-sequence

### A.1.7 [Punctuators]

    (6.4.6) punctuator: one of
                  [ ] ( ) { } . ->
                  ++ -- & * + - ~ !
                  / % << >> < > <= >=                      ==    !=    ^    |   &&   ||
                  ? : ; ...
                  = *= /= %= += -= <<=                     >>=    &=       ^=   |=
                  , # ##
                  <: :> <% %> %: %:%:

### A.1.8 [Header names]

    (6.4.7) header-name:
                  < h-char-sequence >
                  " q-char-sequence "
    (6.4.7) h-char-sequence:
                  h-char
                  h-char-sequence h-char
    (6.4.7) h-char:
                  any member of the source character set except
                               the new-line character and >
    (6.4.7) q-char-sequence:
                  q-char
                  q-char-sequence q-char
    (6.4.7) q-char:
                  any member of the source character set except
                               the new-line character and "

### A.1.9 [Preprocessing numbers]

    (6.4.8) pp-number:
                  digit
                  . digit
                  pp-number digit
                  pp-number identifier-nondigit
                  pp-number e sign
                  pp-number E sign
                  pp-number p sign
                  pp-number P sign
                  pp-number .

### A.2 [Phrase structure grammar]

### A.2.1 [Expressions]

    (6.5.1) primary-expression:
                  identifier
                  constant
                  string-literal
                  ( expression )
                  generic-selection
    (6.5.1.1) generic-selection:
                  _Generic ( assignment-expression , generic-assoc-list )
    (6.5.1.1) generic-assoc-list:
                  generic-association
                  generic-assoc-list , generic-association
    (6.5.1.1) generic-association:
                  type-name : assignment-expression
                  default : assignment-expression
    (6.5.2) postfix-expression:
                   primary-expression
                   postfix-expression [ expression ]
                   postfix-expression ( argument-expression-listopt )
                   postfix-expression . identifier
                   postfix-expression -> identifier
                   postfix-expression ++
                   postfix-expression --
                   ( type-name ) { initializer-list }
                   ( type-name ) { initializer-list , }
    (6.5.2) argument-expression-list:
                 assignment-expression
                 argument-expression-list , assignment-expression
    (6.5.3) unary-expression:
                  postfix-expression
                  ++ unary-expression
                  -- unary-expression
                  unary-operator cast-expression
                  sizeof unary-expression
                  sizeof ( type-name )
                  _Alignof ( type-name )
    (6.5.3) unary-operator: one of
                  & * + - ~             !
    (6.5.4) cast-expression:
                   unary-expression
                   ( type-name ) cast-expression
    (6.5.5) multiplicative-expression:
                   cast-expression
                   multiplicative-expression * cast-expression
                   multiplicative-expression / cast-expression
                   multiplicative-expression % cast-expression
    (6.5.6) additive-expression:
                   multiplicative-expression
                   additive-expression + multiplicative-expression
                   additive-expression - multiplicative-expression
    (6.5.7) shift-expression:
                    additive-expression
                    shift-expression << additive-expression
                    shift-expression >> additive-expression
    (6.5.8) relational-expression:
                   shift-expression
                   relational-expression < shift-expression
                   relational-expression > shift-expression
                   relational-expression <= shift-expression
                   relational-expression >= shift-expression
    (6.5.9) equality-expression:
                   relational-expression
                   equality-expression == relational-expression
                   equality-expression != relational-expression
    (6.5.10) AND-expression:
                 equality-expression
                 AND-expression & equality-expression
    (6.5.11) exclusive-OR-expression:
                  AND-expression
                  exclusive-OR-expression ^ AND-expression
    (6.5.12) inclusive-OR-expression:
                   exclusive-OR-expression
                   inclusive-OR-expression | exclusive-OR-expression
    (6.5.13) logical-AND-expression:
                  inclusive-OR-expression
                  logical-AND-expression && inclusive-OR-expression
    (6.5.14) logical-OR-expression:
                  logical-AND-expression
                  logical-OR-expression || logical-AND-expression
    (6.5.15) conditional-expression:
                  logical-OR-expression
                  logical-OR-expression ? expression : conditional-expression
    (6.5.16) assignment-expression:
                  conditional-expression
                  unary-expression assignment-operator assignment-expression
    (6.5.16) assignment-operator: one of
                  = *= /= %= +=                -=    <<=     >>=       &=   ^=   |=
    (6.5.17) expression:
                  assignment-expression
                  expression , assignment-expression
    (6.6) constant-expression:
                  conditional-expression

### A.2.2 [Declarations]

    (6.7) declaration:
                   declaration-specifiers init-declarator-listopt ;
                   static_assert-declaration
    (6.7) declaration-specifiers:
                   storage-class-specifier declaration-specifiersopt
                   type-specifier declaration-specifiersopt
                   type-qualifier declaration-specifiersopt
                   function-specifier declaration-specifiersopt
                   alignment-specifier declaration-specifiersopt
    (6.7) init-declarator-list:
                   init-declarator
                   init-declarator-list , init-declarator
    (6.7) init-declarator:
                   declarator
                   declarator = initializer
    (6.7.1) storage-class-specifier:
                  typedef
                  extern
                  static
                  _Thread_local
                  auto
                  register
    (6.7.2) type-specifier:
                   void
                   char
                   short
                   int
                   long
                   float
                   double
                   signed
                   unsigned
                   _Bool
                   _Complex
                   atomic-type-specifier
                   struct-or-union-specifier
                   enum-specifier
                   typedef-name
    (6.7.2.1) struct-or-union-specifier:
                   struct-or-union identifieropt { struct-declaration-list }
                   struct-or-union identifier
    (6.7.2.1) struct-or-union:
                   struct
                   union
    (6.7.2.1) struct-declaration-list:
                   struct-declaration
                   struct-declaration-list struct-declaration
    (6.7.2.1) struct-declaration:
                   specifier-qualifier-list struct-declarator-listopt ;
                   static_assert-declaration
    (6.7.2.1) specifier-qualifier-list:
                   type-specifier specifier-qualifier-listopt
                   type-qualifier specifier-qualifier-listopt
    (6.7.2.1) struct-declarator-list:
                   struct-declarator
                   struct-declarator-list , struct-declarator
    (6.7.2.1) struct-declarator:
                   declarator
                   declaratoropt : constant-expression
    (6.7.2.2) enum-specifier:
                  enum identifieropt { enumerator-list }
                  enum identifieropt { enumerator-list , }
                  enum identifier
    (6.7.2.2) enumerator-list:
                  enumerator
                  enumerator-list , enumerator
    (6.7.2.2) enumerator:
                  enumeration-constant
                  enumeration-constant = constant-expression
    (6.7.2.4) atomic-type-specifier:
                  _Atomic ( type-name )
    (6.7.3) type-qualifier:
                  const
                  restrict
                  volatile
                  _Atomic
    (6.7.4) function-specifier:
                   inline
                   _Noreturn
    (6.7.5) alignment-specifier:
                  _Alignas ( type-name )
                  _Alignas ( constant-expression )
    (6.7.6) declarator:
                  pointeropt direct-declarator
    (6.7.6) direct-declarator:
                   identifier
                   ( declarator )
                   direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
                   direct-declarator [ static type-qualifier-listopt assignment-expression ]
                   direct-declarator [ type-qualifier-list static assignment-expression ]
                   direct-declarator [ type-qualifier-listopt * ]
                   direct-declarator ( parameter-type-list )
                   direct-declarator ( identifier-listopt )
    (6.7.6) pointer:
                   * type-qualifier-listopt
                   * type-qualifier-listopt pointer
    (6.7.6) type-qualifier-list:
                  type-qualifier
                  type-qualifier-list type-qualifier
    (6.7.6) parameter-type-list:
                 parameter-list
                 parameter-list , ...
    (6.7.6) parameter-list:
                 parameter-declaration
                 parameter-list , parameter-declaration
    (6.7.6) parameter-declaration:
                 declaration-specifiers declarator
                 declaration-specifiers abstract-declaratoropt
    (6.7.6) identifier-list:
                    identifier
                    identifier-list , identifier
    (6.7.7) type-name:
                  specifier-qualifier-list abstract-declaratoropt
    (6.7.7) abstract-declarator:
                  pointer
                  pointeropt direct-abstract-declarator
    (6.7.7) direct-abstract-declarator:
                   ( abstract-declarator )
                   direct-abstract-declaratoropt [ type-qualifier-listopt
                                  assignment-expressionopt ]
                   direct-abstract-declaratoropt [ static type-qualifier-listopt
                                  assignment-expression ]
                   direct-abstract-declaratoropt [ type-qualifier-list static
                                  assignment-expression ]
                   direct-abstract-declaratoropt [ * ]
                   direct-abstract-declaratoropt ( parameter-type-listopt )
    (6.7.8) typedef-name:
                  identifier
    (6.7.9) initializer:
                    assignment-expression
                    { initializer-list }
                    { initializer-list , }
    (6.7.9) initializer-list:
                    designationopt initializer
                    initializer-list , designationopt initializer
    (6.7.9) designation:
                  designator-list =
    (6.7.9) designator-list:
                  designator
                  designator-list designator
    (6.7.9) designator:
                  [ constant-expression ]
                  . identifier
    (6.7.10) static_assert-declaration:
                   _Static_assert ( constant-expression , string-literal ) ;

### A.2.3 [Statements]

    (6.8) statement:
                  labeled-statement
                  compound-statement
                  expression-statement
                  selection-statement
                  iteration-statement
                  jump-statement
    (6.8.1) labeled-statement:
                   identifier : statement
                   case constant-expression : statement
                   default : statement
    (6.8.2) compound-statement:
                 { block-item-listopt }
    (6.8.2) block-item-list:
                   block-item
                   block-item-list block-item
    (6.8.2) block-item:
                   declaration
                   statement
    (6.8.3) expression-statement:
                  expressionopt ;
    (6.8.4) selection-statement:
                   if ( expression ) statement
                   if ( expression ) statement else statement
                   switch ( expression ) statement
    (6.8.5) iteration-statement:
                    while ( expression ) statement
                    do statement while ( expression ) ;
                    for ( expressionopt ; expressionopt ; expressionopt ) statement
                    for ( declaration expressionopt ; expressionopt ) statement
    (6.8.6) jump-statement:
                  goto identifier ;
                  continue ;
                  break ;
                  return expressionopt ;

### A.2.4 [External definitions]

    (6.9) translation-unit:
                   external-declaration
                   translation-unit external-declaration
    (6.9) external-declaration:
                   function-definition
                   declaration
    (6.9.1) function-definition:
                   declaration-specifiers declarator declaration-listopt compound-statement
    (6.9.1) declaration-list:
                  declaration
                  declaration-list declaration

### A.3 [Preprocessing directives]

    (6.10) preprocessing-file:
                  groupopt
    (6.10) group:
                    group-part
                    group group-part
    (6.10) group-part:
                  if-section
                  control-line
                  text-line
                  # non-directive
    (6.10) if-section:
                    if-group elif-groupsopt else-groupopt endif-line
    (6.10) if-group:
                   # if     constant-expression new-line groupopt
                   # ifdef identifier new-line groupopt
                   # ifndef identifier new-line groupopt
    (6.10) elif-groups:
                   elif-group
                   elif-groups elif-group
    (6.10) elif-group:
                   # elif        constant-expression new-line groupopt
    (6.10) else-group:
                   # else        new-line groupopt
    (6.10) endif-line:
                   # endif       new-line
    (6.10) control-line:
                  # include pp-tokens new-line
                  # define identifier replacement-list new-line
                  # define identifier lparen identifier-listopt )
                                                  replacement-list new-line
                  # define identifier lparen ... ) replacement-list new-line
                  # define identifier lparen identifier-list , ... )
                                                  replacement-list new-line
                  # undef   identifier new-line
                  # line    pp-tokens new-line
                  # error   pp-tokensopt new-line
                  # pragma pp-tokensopt new-line
                  #         new-line
    (6.10) text-line:
                   pp-tokensopt new-line
    (6.10) non-directive:
                  pp-tokens new-line
    (6.10) lparen:
                     a ( character not immediately preceded by white-space
    (6.10) replacement-list:
                  pp-tokensopt
    (6.10) pp-tokens:
                  preprocessing-token
                  pp-tokens preprocessing-token
    (6.10) new-line:
                  the new-line character

### B. [Annex B (informative) Library summary]

### B.1 [Diagnostics <assert.h>]

    NDEBUG
         static_assert
         void assert(scalar expression);

### B.2 [Complex <complex.h>]

    _ _STDC_NO_COMPLEX_ _        imaginary
         complex                      _Imaginary_I
         _Complex_I                   I
         #pragma STDC CX_LIMITED_RANGE on-off-switch
         double complex cacos(double complex z);
         float complex cacosf(float complex z);
         long double complex cacosl(long double complex z);
         double complex casin(double complex z);
         float complex casinf(float complex z);
         long double complex casinl(long double complex z);
         double complex catan(double complex z);
         float complex catanf(float complex z);
         long double complex catanl(long double complex z);
         double complex ccos(double complex z);
         float complex ccosf(float complex z);
         long double complex ccosl(long double complex z);
         double complex csin(double complex z);
         float complex csinf(float complex z);
         long double complex csinl(long double complex z);
         double complex ctan(double complex z);
         float complex ctanf(float complex z);
         long double complex ctanl(long double complex z);
         double complex cacosh(double complex z);
         float complex cacoshf(float complex z);
         long double complex cacoshl(long double complex z);
         double complex casinh(double complex z);
         float complex casinhf(float complex z);
         long double complex casinhl(long double complex z);
    double complex catanh(double complex z);
    float complex catanhf(float complex z);
    long double complex catanhl(long double complex z);
    double complex ccosh(double complex z);
    float complex ccoshf(float complex z);
    long double complex ccoshl(long double complex z);
    double complex csinh(double complex z);
    float complex csinhf(float complex z);
    long double complex csinhl(long double complex z);
    double complex ctanh(double complex z);
    float complex ctanhf(float complex z);
    long double complex ctanhl(long double complex z);
    double complex cexp(double complex z);
    float complex cexpf(float complex z);
    long double complex cexpl(long double complex z);
    double complex clog(double complex z);
    float complex clogf(float complex z);
    long double complex clogl(long double complex z);
    double cabs(double complex z);
    float cabsf(float complex z);
    long double cabsl(long double complex z);
    double complex cpow(double complex x, double complex y);
    float complex cpowf(float complex x, float complex y);
    long double complex cpowl(long double complex x,
         long double complex y);
    double complex csqrt(double complex z);
    float complex csqrtf(float complex z);
    long double complex csqrtl(long double complex z);
    double carg(double complex z);
    float cargf(float complex z);
    long double cargl(long double complex z);
    double cimag(double complex z);
    float cimagf(float complex z);
    long double cimagl(long double complex z);
    double complex CMPLX(double x, double y);
    float complex CMPLXF(float x, float y);
    long double complex CMPLXL(long double x, long double y);
    double complex conj(double complex z);
    float complex conjf(float complex z);
    long double complex conjl(long double complex z);
    double complex cproj(double complex z);
         float complex cprojf(float complex z);
         long double complex cprojl(long double complex z);
         double creal(double complex z);
         float crealf(float complex z);
         long double creall(long double complex z);

### B.3 [Character handling <ctype.h>]

    int isalnum(int c);
         int isalpha(int c);
         int isblank(int c);
         int iscntrl(int c);
         int isdigit(int c);
         int isgraph(int c);
         int islower(int c);
         int isprint(int c);
         int ispunct(int c);
         int isspace(int c);
         int isupper(int c);
         int isxdigit(int c);
         int tolower(int c);
         int toupper(int c);

### B.4 [Errors <errno.h>]

    EDOM           EILSEQ         ERANGE       errno
         _ _STDC_WANT_LIB_EXT1_ _
         errno_t

### B.5 [Floating-point environment <fenv.h>]

    fenv_t              FE_OVERFLOW        FE_TOWARDZERO
         fexcept_t           FE_UNDERFLOW       FE_UPWARD
         FE_DIVBYZERO        FE_ALL_EXCEPT      FE_DFL_ENV
         FE_INEXACT          FE_DOWNWARD
         FE_INVALID          FE_TONEAREST
         #pragma STDC FENV_ACCESS on-off-switch
         int feclearexcept(int excepts);
         int fegetexceptflag(fexcept_t *flagp, int excepts);
         int feraiseexcept(int excepts);
         int fesetexceptflag(const fexcept_t *flagp,
              int excepts);
         int fetestexcept(int excepts);
         int fegetround(void);
         int fesetround(int round);
         int fegetenv(fenv_t *envp);
         int feholdexcept(fenv_t *envp);
         int fesetenv(const fenv_t *envp);
         int feupdateenv(const fenv_t *envp);

### B.6 [Characteristics of floating types <float.h>]

    FLT_ROUNDS           DBL_DIG                 FLT_MAX
         FLT_EVAL_METHOD      LDBL_DIG                DBL_MAX
         FLT_HAS_SUBNORM      FLT_MIN_EXP             LDBL_MAX
         DBL_HAS_SUBNORM      DBL_MIN_EXP             FLT_EPSILON
         LDBL_HAS_SUBNORM     LDBL_MIN_EXP            DBL_EPSILON
         FLT_RADIX            FLT_MIN_10_EXP          LDBL_EPSILON
         FLT_MANT_DIG         DBL_MIN_10_EXP          FLT_MIN
         DBL_MANT_DIG         LDBL_MIN_10_EXP         DBL_MIN
         LDBL_MANT_DIG        FLT_MAX_EXP             LDBL_MIN
         FLT_DECIMAL_DIG      DBL_MAX_EXP             FLT_TRUE_MIN
         DBL_DECIMAL_DIG      LDBL_MAX_EXP            DBL_TRUE_MIN
         LDBL_DECIMAL_DIG     FLT_MAX_10_EXP          LDBL_TRUE_MIN
         DECIMAL_DIG          DBL_MAX_10_EXP
         FLT_DIG              LDBL_MAX_10_EXP

### B.7 [Format conversion of integer types <inttypes.h>]

    imaxdiv_t
         PRIdN       PRIdLEASTN     PRIdFASTN         PRIdMAX    PRIdPTR
         PRIiN       PRIiLEASTN     PRIiFASTN         PRIiMAX    PRIiPTR
         PRIoN       PRIoLEASTN     PRIoFASTN         PRIoMAX    PRIoPTR
         PRIuN       PRIuLEASTN     PRIuFASTN         PRIuMAX    PRIuPTR
         PRIxN       PRIxLEASTN     PRIxFASTN         PRIxMAX    PRIxPTR
         PRIXN       PRIXLEASTN     PRIXFASTN         PRIXMAX    PRIXPTR
         SCNdN       SCNdLEASTN     SCNdFASTN         SCNdMAX    SCNdPTR
         SCNiN       SCNiLEASTN     SCNiFASTN         SCNiMAX    SCNiPTR
         SCNoN       SCNoLEASTN     SCNoFASTN         SCNoMAX    SCNoPTR
         SCNuN       SCNuLEASTN     SCNuFASTN         SCNuMAX    SCNuPTR
         SCNxN       SCNxLEASTN     SCNxFASTN         SCNxMAX    SCNxPTR
         intmax_t imaxabs(intmax_t j);
         imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
         intmax_t strtoimax(const char * restrict nptr,
                 char ** restrict endptr, int base);
         uintmax_t strtoumax(const char * restrict nptr,
                 char ** restrict endptr, int base);
         intmax_t wcstoimax(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr, int base);
         uintmax_t wcstoumax(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr, int base);

### B.8 [Alternative spellings <iso646.h>]

    and            bitor           not_eq         xor
         and_eq         compl           or             xor_eq
         bitand         not             or_eq

### B.9 [Sizes of integer types <limits.h>]

    CHAR_BIT       CHAR_MAX        INT_MIN        ULONG_MAX
         SCHAR_MIN      MB_LEN_MAX      INT_MAX        LLONG_MIN
         SCHAR_MAX      SHRT_MIN        UINT_MAX       LLONG_MAX
         UCHAR_MAX      SHRT_MAX        LONG_MIN       ULLONG_MAX
         CHAR_MIN       USHRT_MAX       LONG_MAX

### B.10 [Localization <locale.h>]

    struct lconv   LC_ALL          LC_CTYPE       LC_NUMERIC
         NULL           LC_COLLATE      LC_MONETARY    LC_TIME
         char *setlocale(int category, const char *locale);
         struct lconv *localeconv(void);

### B.11 [Mathematics <math.h>]

    float_t             FP_INFINITE           FP_FAST_FMAL
         double_t            FP_NAN                FP_ILOGB0
         HUGE_VAL            FP_NORMAL             FP_ILOGBNAN
         HUGE_VALF           FP_SUBNORMAL          MATH_ERRNO
         HUGE_VALL           FP_ZERO               MATH_ERREXCEPT
         INFINITY            FP_FAST_FMA           math_errhandling
         NAN                 FP_FAST_FMAF
         #pragma STDC FP_CONTRACT on-off-switch
         int fpclassify(real-floating x);
         int isfinite(real-floating x);
         int isinf(real-floating x);
         int isnan(real-floating x);
         int isnormal(real-floating x);
         int signbit(real-floating x);
    double acos(double x);
    float acosf(float x);
    long double acosl(long double x);
    double asin(double x);
    float asinf(float x);
    long double asinl(long double x);
    double atan(double x);
    float atanf(float x);
    long double atanl(long double x);
    double atan2(double y, double x);
    float atan2f(float y, float x);
    long double atan2l(long double y, long double x);
    double cos(double x);
    float cosf(float x);
    long double cosl(long double x);
    double sin(double x);
    float sinf(float x);
    long double sinl(long double x);
    double tan(double x);
    float tanf(float x);
    long double tanl(long double x);
    double acosh(double x);
    float acoshf(float x);
    long double acoshl(long double x);
    double asinh(double x);
    float asinhf(float x);
    long double asinhl(long double x);
    double atanh(double x);
    float atanhf(float x);
    long double atanhl(long double x);
    double cosh(double x);
    float coshf(float x);
    long double coshl(long double x);
    double sinh(double x);
    float sinhf(float x);
    long double sinhl(long double x);
    double tanh(double x);
    float tanhf(float x);
    long double tanhl(long double x);
    double exp(double x);
    float expf(float x);
    long double expl(long double x);
    double exp2(double x);
    float exp2f(float x);
    long double exp2l(long double x);
    double expm1(double x);
    float expm1f(float x);
    long double expm1l(long double x);
    double frexp(double value, int *exp);
    float frexpf(float value, int *exp);
    long double frexpl(long double value, int *exp);
    int ilogb(double x);
    int ilogbf(float x);
    int ilogbl(long double x);
    double ldexp(double x, int exp);
    float ldexpf(float x, int exp);
    long double ldexpl(long double x, int exp);
    double log(double x);
    float logf(float x);
    long double logl(long double x);
    double log10(double x);
    float log10f(float x);
    long double log10l(long double x);
    double log1p(double x);
    float log1pf(float x);
    long double log1pl(long double x);
    double log2(double x);
    float log2f(float x);
    long double log2l(long double x);
    double logb(double x);
    float logbf(float x);
    long double logbl(long double x);
    double modf(double value, double *iptr);
    float modff(float value, float *iptr);
    long double modfl(long double value, long double *iptr);
    double scalbn(double x, int n);
    float scalbnf(float x, int n);
    long double scalbnl(long double x, int n);
    double scalbln(double x, long int n);
    float scalblnf(float x, long int n);
    long double scalblnl(long double x, long int n);
    double cbrt(double x);
    float cbrtf(float x);
    long double cbrtl(long double x);
    double fabs(double x);
    float fabsf(float x);
    long double fabsl(long double x);
    double hypot(double x, double y);
    float hypotf(float x, float y);
    long double hypotl(long double x, long double y);
    double pow(double x, double y);
    float powf(float x, float y);
    long double powl(long double x, long double y);
    double sqrt(double x);
    float sqrtf(float x);
    long double sqrtl(long double x);
    double erf(double x);
    float erff(float x);
    long double erfl(long double x);
    double erfc(double x);
    float erfcf(float x);
    long double erfcl(long double x);
    double lgamma(double x);
    float lgammaf(float x);
    long double lgammal(long double x);
    double tgamma(double x);
    float tgammaf(float x);
    long double tgammal(long double x);
    double ceil(double x);
    float ceilf(float x);
    long double ceill(long double x);
    double floor(double x);
    float floorf(float x);
    long double floorl(long double x);
    double nearbyint(double x);
    float nearbyintf(float x);
    long double nearbyintl(long double x);
    double rint(double x);
    float rintf(float x);
    long double rintl(long double x);
    long int lrint(double x);
    long int lrintf(float x);
    long int lrintl(long double x);
    long long int llrint(double x);
    long long int llrintf(float x);
    long long int llrintl(long double x);
    double round(double x);
    float roundf(float x);
    long double roundl(long double x);
    long int lround(double x);
    long int lroundf(float x);
    long int lroundl(long double x);
    long long int llround(double x);
    long long int llroundf(float x);
    long long int llroundl(long double x);
    double trunc(double x);
    float truncf(float x);
    long double truncl(long double x);
    double fmod(double x, double y);
    float fmodf(float x, float y);
    long double fmodl(long double x, long double y);
    double remainder(double x, double y);
    float remainderf(float x, float y);
    long double remainderl(long double x, long double y);
    double remquo(double x, double y, int *quo);
    float remquof(float x, float y, int *quo);
    long double remquol(long double x, long double y,
         int *quo);
    double copysign(double x, double y);
    float copysignf(float x, float y);
    long double copysignl(long double x, long double y);
    double nan(const char *tagp);
    float nanf(const char *tagp);
    long double nanl(const char *tagp);
    double nextafter(double x, double y);
    float nextafterf(float x, float y);
    long double nextafterl(long double x, long double y);
    double nexttoward(double x, long double y);
    float nexttowardf(float x, long double y);
    long double nexttowardl(long double x, long double y);
    double fdim(double x, double y);
    float fdimf(float x, float y);
    long double fdiml(long double x, long double y);
    double fmax(double x, double y);
         float fmaxf(float x, float y);
         long double fmaxl(long double x, long double y);
         double fmin(double x, double y);
         float fminf(float x, float y);
         long double fminl(long double x, long double y);
         double fma(double x, double y, double z);
         float fmaf(float x, float y, float z);
         long double fmal(long double x, long double y,
              long double z);
         int isgreater(real-floating x, real-floating y);
         int isgreaterequal(real-floating x, real-floating y);
         int isless(real-floating x, real-floating y);
         int islessequal(real-floating x, real-floating y);
         int islessgreater(real-floating x, real-floating y);
         int isunordered(real-floating x, real-floating y);

### B.12 [Nonlocal jumps <setjmp.h>]

    jmp_buf
         int setjmp(jmp_buf env);
         _Noreturn void longjmp(jmp_buf env, int val);

### B.13 [Signal handling <signal.h>]

    sig_atomic_t   SIG_IGN        SIGILL         SIGTERM
         SIG_DFL        SIGABRT        SIGINT
         SIG_ERR        SIGFPE         SIGSEGV
         void (*signal(int sig, void (*func)(int)))(int);
         int raise(int sig);

### B.14 [Alignment <stdalign.h>]

    alignas
         _ _alignas_is_defined

### B.15 [Variable arguments <stdarg.h>]

    va_list
         type va_arg(va_list ap, type);
         void va_copy(va_list dest, va_list src);
         void va_end(va_list ap);
         void va_start(va_list ap, parmN);

### B.16 [Atomics <stdatomic.h>]

    ATOMIC_BOOL_LOCK_FREE       atomic_uint
         ATOMIC_CHAR_LOCK_FREE       atomic_long
         ATOMIC_CHAR16_T_LOCK_FREE   atomic_ulong
         ATOMIC_CHAR32_T_LOCK_FREE   atomic_llong
         ATOMIC_WCHAR_T_LOCK_FREE    atomic_ullong
         ATOMIC_SHORT_LOCK_FREE      atomic_char16_t
         ATOMIC_INT_LOCK_FREE        atomic_char32_t
         ATOMIC_LONG_LOCK_FREE       atomic_wchar_t
         ATOMIC_LLONG_LOCK_FREE      atomic_int_least8_t
         ATOMIC_POINTER_LOCK_FREE    atomic_uint_least8_t
         ATOMIC_FLAG_INIT            atomic_int_least16_t
         memory_order                atomic_uint_least16_t
         atomic_flag                 atomic_int_least32_t
         memory_order_relaxed      ∗ atomic_uint_least32_t
         memory_order_consume        atomic_int_least64_t
         memory_order_acquire        atomic_uint_least64_t
         memory_order_release        atomic_int_fast8_t
         memory_order_acq_rel        atomic_uint_fast8_t
         memory_order_seq_cst        atomic_int_fast16_t
         atomic_bool                 atomic_uint_fast16_t
         atomic_char                 atomic_int_fast32_t
         atomic_schar                atomic_uint_fast32_t
         atomic_uchar                atomic_int_fast64_t
         atomic_short                atomic_uint_fast64_t
         atomic_ushort               atomic_intptr_t
         atomic_int                  atomic_uintptr_t
    atomic_size_t              atomic_intmax_t
    atomic_ptrdiff_t           atomic_uintmax_t
    #define ATOMIC_VAR_INIT(C value)
    void atomic_init(volatile A *obj, C value);
    type kill_dependency(type y);
    void atomic_thread_fence(memory_order order);
    void atomic_signal_fence(memory_order order);
    _Bool atomic_is_lock_free(const volatile A *obj);
    void atomic_store(volatile A *object, C desired);
    void atomic_store_explicit(volatile A *object,
          C desired, memory_order order);
    C atomic_load(volatile A *object);
    C atomic_load_explicit(volatile A *object,
          memory_order order);
    C atomic_exchange(volatile A *object, C desired);
    C atomic_exchange_explicit(volatile A *object,
          C desired, memory_order order);
    _Bool atomic_compare_exchange_strong(volatile A *object,
          C *expected, C desired);
    _Bool atomic_compare_exchange_strong_explicit(
          volatile A *object, C *expected, C desired,
          memory_order success, memory_order failure);
    _Bool atomic_compare_exchange_weak(volatile A *object,
          C *expected, C desired);
    _Bool atomic_compare_exchange_weak_explicit(
          volatile A *object, C *expected, C desired,
          memory_order success, memory_order failure);
    C atomic_fetch_key(volatile A *object, M operand);
    C atomic_fetch_key_explicit(volatile A *object,
          M operand, memory_order order);
    _Bool atomic_flag_test_and_set(
          volatile atomic_flag *object);
    _Bool atomic_flag_test_and_set_explicit(
          volatile atomic_flag *object, memory_order order);
    void atomic_flag_clear(volatile atomic_flag *object);
    void atomic_flag_clear_explicit(
          volatile atomic_flag *object, memory_order order);

### B.17 [Boolean type and values <stdbool.h>]

    bool
         true
         false
         _ _bool_true_false_are_defined

### B.18 [Common definitions <stddef.h>]

    ptrdiff_t       max_align_t     NULL
         size_t          wchar_t
         offsetof(type, member-designator)
         _ _STDC_WANT_LIB_EXT1_ _
         rsize_t

### B.19 [Integer types <stdint.h>]

    intN_t               INT_LEASTN_MIN    PTRDIFF_MAX
         uintN_t              INT_LEASTN_MAX    SIG_ATOMIC_MIN
         int_leastN_t         UINT_LEASTN_MAX   SIG_ATOMIC_MAX
         uint_leastN_t        INT_FASTN_MIN     SIZE_MAX
         int_fastN_t          INT_FASTN_MAX     WCHAR_MIN
         uint_fastN_t         UINT_FASTN_MAX    WCHAR_MAX
         intptr_t             INTPTR_MIN        WINT_MIN
         uintptr_t            INTPTR_MAX        WINT_MAX
         intmax_t             UINTPTR_MAX       INTN_C(value)
         uintmax_t            INTMAX_MIN        UINTN_C(value)
         INTN_MIN             INTMAX_MAX        INTMAX_C(value)
         INTN_MAX             UINTMAX_MAX       UINTMAX_C(value)
         UINTN_MAX            PTRDIFF_MIN
         _ _STDC_WANT_LIB_EXT1_ _
         RSIZE_MAX

### B.20 [Input/output <stdio.h>]

    size_t        _IOLBF       FILENAME_MAX   TMP_MAX
         FILE          _IONBF       L_tmpnam       stderr
         fpos_t        BUFSIZ       SEEK_CUR       stdin
         NULL          EOF          SEEK_END       stdout
         _IOFBF        FOPEN_MAX    SEEK_SET
         int remove(const char *filename);
         int rename(const char *old, const char *new);
         FILE *tmpfile(void);
         char *tmpnam(char *s);
         int fclose(FILE *stream);
         int fflush(FILE *stream);
         FILE *fopen(const char * restrict filename,
              const char * restrict mode);
         FILE *freopen(const char * restrict filename,
              const char * restrict mode,
              FILE * restrict stream);
         void setbuf(FILE * restrict stream,
              char * restrict buf);
         int setvbuf(FILE * restrict stream,
              char * restrict buf,
              int mode, size_t size);
         int fprintf(FILE * restrict stream,
              const char * restrict format, ...);
         int fscanf(FILE * restrict stream,
              const char * restrict format, ...);
         int printf(const char * restrict format, ...);
         int scanf(const char * restrict format, ...);
         int snprintf(char * restrict s, size_t n,
              const char * restrict format, ...);
         int sprintf(char * restrict s,
              const char * restrict format, ...);
         int sscanf(const char * restrict s,
              const char * restrict format, ...);
         int vfprintf(FILE * restrict stream,
              const char * restrict format, va_list arg);
         int vfscanf(FILE * restrict stream,
              const char * restrict format, va_list arg);
         int vprintf(const char * restrict format, va_list arg);
         int vscanf(const char * restrict format, va_list arg);
    int vsnprintf(char * restrict s, size_t n,
         const char * restrict format, va_list arg);
    int vsprintf(char * restrict s,
         const char * restrict format, va_list arg);
    int vsscanf(const char * restrict s,
         const char * restrict format, va_list arg);
    int fgetc(FILE *stream);
    char *fgets(char * restrict s, int n,
         FILE * restrict stream);
    int fputc(int c, FILE *stream);
    int fputs(const char * restrict s,
         FILE * restrict stream);
    int getc(FILE *stream);
    int getchar(void);
    int putc(int c, FILE *stream);
    int putchar(int c);
    int puts(const char *s);
    int ungetc(int c, FILE *stream);
    size_t fread(void * restrict ptr,
         size_t size, size_t nmemb,
         FILE * restrict stream);
    size_t fwrite(const void * restrict ptr,
         size_t size, size_t nmemb,
         FILE * restrict stream);
    int fgetpos(FILE * restrict stream,
         fpos_t * restrict pos);
    int fseek(FILE *stream, long int offset, int whence);
    int fsetpos(FILE *stream, const fpos_t *pos);
    long int ftell(FILE *stream);
    void rewind(FILE *stream);
    void clearerr(FILE *stream);
    int feof(FILE *stream);
    int ferror(FILE *stream);
    void perror(const char *s);
    _ _STDC_WANT_LIB_EXT1_ _
    L_tmpnam_s    TMP_MAX_S    errno_t       rsize_t
    errno_t tmpfile_s(FILE * restrict * restrict streamptr);
    errno_t tmpnam_s(char *s, rsize_t maxsize);
    errno_t fopen_s(FILE * restrict * restrict streamptr,
         const char * restrict filename,
         const char * restrict mode);
    errno_t freopen_s(FILE * restrict * restrict newstreamptr,
         const char * restrict filename,
         const char * restrict mode,
         FILE * restrict stream);
    int fprintf_s(FILE * restrict stream,
         const char * restrict format, ...);
    int fscanf_s(FILE * restrict stream,
         const char * restrict format, ...);
    int printf_s(const char * restrict format, ...);
    int scanf_s(const char * restrict format, ...);
    int snprintf_s(char * restrict s, rsize_t n,
         const char * restrict format, ...);
    int sprintf_s(char * restrict s, rsize_t n,
         const char * restrict format, ...);
    int sscanf_s(const char * restrict s,
         const char * restrict format, ...);
    int vfprintf_s(FILE * restrict stream,
         const char * restrict format,
         va_list arg);
    int vfscanf_s(FILE * restrict stream,
         const char * restrict format,
         va_list arg);
    int vprintf_s(const char * restrict format,
         va_list arg);
    int vscanf_s(const char * restrict format,
         va_list arg);
    int vsnprintf_s(char * restrict s, rsize_t n,
         const char * restrict format,
         va_list arg);
    int vsprintf_s(char * restrict s, rsize_t n,
         const char * restrict format,
         va_list arg);
    int vsscanf_s(const char * restrict s,
         const char * restrict format,
         va_list arg);
    char *gets_s(char *s, rsize_t n);

### B.21 [General utilities <stdlib.h>]

    size_t         ldiv_t          EXIT_FAILURE   MB_CUR_MAX
         wchar_t        lldiv_t         EXIT_SUCCESS
         div_t          NULL            RAND_MAX
         double atof(const char *nptr);
         int atoi(const char *nptr);
         long int atol(const char *nptr);
         long long int atoll(const char *nptr);
         double strtod(const char * restrict nptr,
              char ** restrict endptr);
         float strtof(const char * restrict nptr,
              char ** restrict endptr);
         long double strtold(const char * restrict nptr,
              char ** restrict endptr);
         long int strtol(const char * restrict nptr,
              char ** restrict endptr, int base);
         long long int strtoll(const char * restrict nptr,
              char ** restrict endptr, int base);
         unsigned long int strtoul(
              const char * restrict nptr,
              char ** restrict endptr, int base);
         unsigned long long int strtoull(
              const char * restrict nptr,
              char ** restrict endptr, int base);
         int rand(void);
         void srand(unsigned int seed);
         void *aligned_alloc(size_t alignment, size_t size);
         void *calloc(size_t nmemb, size_t size);
         void free(void *ptr);
         void *malloc(size_t size);
         void *realloc(void *ptr, size_t size);
         _Noreturn void abort(void);
         int atexit(void (*func)(void));
         int at_quick_exit(void (*func)(void));
         _Noreturn void exit(int status);
         _Noreturn void _Exit(int status);
         char *getenv(const char *name);
         _Noreturn void quick_exit(int status);
         int system(const char *string);
    void *bsearch(const void *key, const void *base,
         size_t nmemb, size_t size,
         int (*compar)(const void *, const void *));
    void qsort(void *base, size_t nmemb, size_t size,
         int (*compar)(const void *, const void *));
    int abs(int j);
    long int labs(long int j);
    long long int llabs(long long int j);
    div_t div(int numer, int denom);
    ldiv_t ldiv(long int numer, long int denom);
    lldiv_t lldiv(long long int numer,
         long long int denom);
    int mblen(const char *s, size_t n);
    int mbtowc(wchar_t * restrict pwc,
         const char * restrict s, size_t n);
    int wctomb(char *s, wchar_t wchar);
    size_t mbstowcs(wchar_t * restrict pwcs,
         const char * restrict s, size_t n);
    size_t wcstombs(char * restrict s,
         const wchar_t * restrict pwcs, size_t n);
    _ _STDC_WANT_LIB_EXT1_ _
    errno_t
    rsize_t
    constraint_handler_t
    constraint_handler_t set_constraint_handler_s(
         constraint_handler_t handler);
    void abort_handler_s(
         const char * restrict msg,
         void * restrict ptr,
         errno_t error);
    void ignore_handler_s(
         const char * restrict msg,
         void * restrict ptr,
         errno_t error);
    errno_t getenv_s(size_t * restrict len,
              char * restrict value, rsize_t maxsize,
              const char * restrict name);
         void *bsearch_s(const void *key, const void *base,
              rsize_t nmemb, rsize_t size,
              int (*compar)(const void *k, const void *y,
                              void *context),
              void *context);
         errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
              int (*compar)(const void *x, const void *y,
                              void *context),
              void *context);
         errno_t wctomb_s(int * restrict status,
              char * restrict s,
              rsize_t smax,
              wchar_t wc);
         errno_t mbstowcs_s(size_t * restrict retval,
              wchar_t * restrict dst, rsize_t dstmax,
              const char * restrict src, rsize_t len);
         errno_t wcstombs_s(size_t * restrict retval,
              char * restrict dst, rsize_t dstmax,
              const wchar_t * restrict src, rsize_t len);

### B.22 [_Noreturn <stdnoreturn.h>]

    noreturn

### B.23 [String handling <string.h>]

    size_t
         NULL
         void *memcpy(void * restrict s1,
              const void * restrict s2, size_t n);
         void *memmove(void *s1, const void *s2, size_t n);
         char *strcpy(char * restrict s1,
              const char * restrict s2);
         char *strncpy(char * restrict s1,
              const char * restrict s2, size_t n);
         char *strcat(char * restrict s1,
              const char * restrict s2);
         char *strncat(char * restrict s1,
              const char * restrict s2, size_t n);
         int memcmp(const void *s1, const void *s2, size_t n);
         int strcmp(const char *s1, const char *s2);
         int strcoll(const char *s1, const char *s2);
         int strncmp(const char *s1, const char *s2, size_t n);
    size_t strxfrm(char * restrict s1,
         const char * restrict s2, size_t n);
    void *memchr(const void *s, int c, size_t n);
    char *strchr(const char *s, int c);
    size_t strcspn(const char *s1, const char *s2);
    char *strpbrk(const char *s1, const char *s2);
    char *strrchr(const char *s, int c);
    size_t strspn(const char *s1, const char *s2);
    char *strstr(const char *s1, const char *s2);
    char *strtok(char * restrict s1,
         const char * restrict s2);
    void *memset(void *s, int c, size_t n);
    char *strerror(int errnum);
    size_t strlen(const char *s);
    _ _STDC_WANT_LIB_EXT1_ _
    errno_t
    rsize_t
    errno_t memcpy_s(void * restrict s1, rsize_t s1max,
         const void * restrict s2, rsize_t n);
    errno_t memmove_s(void *s1, rsize_t s1max,
         const void *s2, rsize_t n);
    errno_t strcpy_s(char * restrict s1,
         rsize_t s1max,
         const char * restrict s2);
    errno_t strncpy_s(char * restrict s1,
         rsize_t s1max,
         const char * restrict s2,
         rsize_t n);
    errno_t strcat_s(char * restrict s1,
         rsize_t s1max,
         const char * restrict s2);
    errno_t strncat_s(char * restrict s1,
         rsize_t s1max,
         const char * restrict s2,
         rsize_t n);
    char *strtok_s(char * restrict s1,
         rsize_t * restrict s1max,
         const char * restrict s2,
         char ** restrict ptr);
    errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
         errno_t strerror_s(char *s, rsize_t maxsize,
              errno_t errnum);
         size_t strerrorlen_s(errno_t errnum);
         size_t strnlen_s(const char *s, size_t maxsize);

### B.24 [Type-generic math <tgmath.h>]

    acos          sqrt             fmod            nextafter
         asin          fabs             frexp           nexttoward
         atan          atan2            hypot           remainder
         acosh         cbrt             ilogb           remquo
         asinh         ceil             ldexp           rint
         atanh         copysign         lgamma          round
         cos           erf              llrint          scalbn
         sin           erfc             llround         scalbln
         tan           exp2             log10           tgamma
         cosh          expm1            log1p           trunc
         sinh          fdim             log2            carg
         tanh          floor            logb            cimag
         exp           fma              lrint           conj
         log           fmax             lround          cproj
         pow           fmin             nearbyint       creal

### B.25 [Threads <threads.h>]

    thread_local                   once_flag
         ONCE_FLAG_INIT                 mtx_plain                    ∗
         TSS_DTOR_ITERATIONS            mtx_recursive
         cnd_t                          mtx_timed
         thrd_t                         thrd_timedout
         tss_t                          thrd_success
         mtx_t                          thrd_busy
         tss_dtor_t                     thrd_error
         thrd_start_t                   thrd_nomem
         void call_once(once_flag *flag, void (*func)(void));
         int cnd_broadcast(cnd_t *cond);
         void cnd_destroy(cnd_t *cond);
         int cnd_init(cnd_t *cond);
         int cnd_signal(cnd_t *cond);
         int cnd_timedwait(cnd_t *restrict cond,
              mtx_t *restrict mtx,
              const struct timespec *restrict ts);
         int cnd_wait(cnd_t *cond, mtx_t *mtx);
         void mtx_destroy(mtx_t *mtx);
         int mtx_init(mtx_t *mtx, int type);
         int mtx_lock(mtx_t *mtx);
         int mtx_timedlock(mtx_t *restrict mtx,
              const struct timespec *restrict ts);
         int mtx_trylock(mtx_t *mtx);
         int mtx_unlock(mtx_t *mtx);
         int thrd_create(thrd_t *thr, thrd_start_t func,
              void *arg);
         thrd_t thrd_current(void);
         int thrd_detach(thrd_t thr);
         int thrd_equal(thrd_t thr0, thrd_t thr1);
         _Noreturn void thrd_exit(int res);
         int thrd_join(thrd_t thr, int *res);
         int thrd_sleep(const struct timespec *duration,
              struct timespec *remaining);
         void thrd_yield(void);
         int tss_create(tss_t *key, tss_dtor_t dtor);
         void tss_delete(tss_t key);
         void *tss_get(tss_t key);
         int tss_set(tss_t key, void *val);

### B.26 [Date and time <time.h>]

    NULL               size_t           struct timespec
         CLOCKS_PER_SEC     clock_t          struct tm
         TIME_UTC           time_t
         clock_t clock(void);
         double difftime(time_t time1, time_t time0);
         time_t mktime(struct tm *timeptr);
         time_t time(time_t *timer);
         int timespec_get(timespec *ts, int base);
         char *asctime(const struct tm *timeptr);
         char *ctime(const time_t *timer);
         struct tm *gmtime(const time_t *timer);
         struct tm *localtime(const time_t *timer);
         size_t strftime(char * restrict s,
              size_t maxsize,
              const char * restrict format,
              const struct tm * restrict timeptr);
         _ _STDC_WANT_LIB_EXT1_ _
         errno_t
         rsize_t
         errno_t asctime_s(char *s, rsize_t maxsize,
              const struct tm *timeptr);
         errno_t ctime_s(char *s, rsize_t maxsize,
              const time_t *timer);
         struct tm *gmtime_s(const time_t * restrict timer,
              struct tm * restrict result);
         struct tm *localtime_s(const time_t * restrict timer,
              struct tm * restrict result);

### B.27 [Unicode utilities <uchar.h>]

    mbstate_t       size_t           char16_t       char32_t
         size_t mbrtoc16(char16_t * restrict pc16,
              const char * restrict s, size_t n,
              mbstate_t * restrict ps);
         size_t c16rtomb(char * restrict s, char16_t c16,
              mbstate_t * restrict ps);
         size_t mbrtoc32(char32_t * restrict pc32,
              const char * restrict s, size_t n,
              mbstate_t * restrict ps);
         size_t c32rtomb(char * restrict s, char32_t c32,
              mbstate_t * restrict ps);

### B.28 [Extended multibyte/wide character utilities <wchar.h>]

    wchar_t              wint_t                 WCHAR_MAX
         size_t               struct tm              WCHAR_MIN
         mbstate_t            NULL                   WEOF
         int fwprintf(FILE * restrict stream,
              const wchar_t * restrict format, ...);
         int fwscanf(FILE * restrict stream,
              const wchar_t * restrict format, ...);
         int swprintf(wchar_t * restrict s, size_t n,
              const wchar_t * restrict format, ...);
         int swscanf(const wchar_t * restrict s,
              const wchar_t * restrict format, ...);
         int vfwprintf(FILE * restrict stream,
              const wchar_t * restrict format, va_list arg);
    int vfwscanf(FILE * restrict stream,
         const wchar_t * restrict format, va_list arg);
    int vswprintf(wchar_t * restrict s, size_t n,
         const wchar_t * restrict format, va_list arg);
    int vswscanf(const wchar_t * restrict s,
         const wchar_t * restrict format, va_list arg);
    int vwprintf(const wchar_t * restrict format,
         va_list arg);
    int vwscanf(const wchar_t * restrict format,
         va_list arg);
    int wprintf(const wchar_t * restrict format, ...);
    int wscanf(const wchar_t * restrict format, ...);
    wint_t fgetwc(FILE *stream);
    wchar_t *fgetws(wchar_t * restrict s, int n,
         FILE * restrict stream);
    wint_t fputwc(wchar_t c, FILE *stream);
    int fputws(const wchar_t * restrict s,
         FILE * restrict stream);
    int fwide(FILE *stream, int mode);
    wint_t getwc(FILE *stream);
    wint_t getwchar(void);
    wint_t putwc(wchar_t c, FILE *stream);
    wint_t putwchar(wchar_t c);
    wint_t ungetwc(wint_t c, FILE *stream);
    double wcstod(const wchar_t * restrict nptr,
         wchar_t ** restrict endptr);
    float wcstof(const wchar_t * restrict nptr,
         wchar_t ** restrict endptr);
    long double wcstold(const wchar_t * restrict nptr,
         wchar_t ** restrict endptr);
    long int wcstol(const wchar_t * restrict nptr,
         wchar_t ** restrict endptr, int base);
    long long int wcstoll(const wchar_t * restrict nptr,
         wchar_t ** restrict endptr, int base);
    unsigned long int wcstoul(const wchar_t * restrict nptr,
         wchar_t ** restrict endptr, int base);
    unsigned long long int wcstoull(
         const wchar_t * restrict nptr,
         wchar_t ** restrict endptr, int base);
    wchar_t *wcscpy(wchar_t * restrict s1,
         const wchar_t * restrict s2);
    wchar_t *wcsncpy(wchar_t * restrict s1,
         const wchar_t * restrict s2, size_t n);
    wchar_t *wmemcpy(wchar_t * restrict s1,
         const wchar_t * restrict s2, size_t n);
    wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
         size_t n);
    wchar_t *wcscat(wchar_t * restrict s1,
         const wchar_t * restrict s2);
    wchar_t *wcsncat(wchar_t * restrict s1,
         const wchar_t * restrict s2, size_t n);
    int wcscmp(const wchar_t *s1, const wchar_t *s2);
    int wcscoll(const wchar_t *s1, const wchar_t *s2);
    int wcsncmp(const wchar_t *s1, const wchar_t *s2,
         size_t n);
    size_t wcsxfrm(wchar_t * restrict s1,
         const wchar_t * restrict s2, size_t n);
    int wmemcmp(const wchar_t *s1, const wchar_t *s2,
         size_t n);
    wchar_t *wcschr(const wchar_t *s, wchar_t c);
    size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
    wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
    wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
    size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
    wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
    wchar_t *wcstok(wchar_t * restrict s1,
         const wchar_t * restrict s2,
         wchar_t ** restrict ptr);
    wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
    size_t wcslen(const wchar_t *s);
    wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
    size_t wcsftime(wchar_t * restrict s, size_t maxsize,
         const wchar_t * restrict format,
         const struct tm * restrict timeptr);
    wint_t btowc(int c);
    int wctob(wint_t c);
    int mbsinit(const mbstate_t *ps);
    size_t mbrlen(const char * restrict s, size_t n,
         mbstate_t * restrict ps);
    size_t mbrtowc(wchar_t * restrict pwc,
         const char * restrict s, size_t n,
         mbstate_t * restrict ps);
    size_t wcrtomb(char * restrict s, wchar_t wc,
         mbstate_t * restrict ps);
    size_t mbsrtowcs(wchar_t * restrict dst,
         const char ** restrict src, size_t len,
         mbstate_t * restrict ps);
    size_t wcsrtombs(char * restrict dst,
         const wchar_t ** restrict src, size_t len,
         mbstate_t * restrict ps);
    _ _STDC_WANT_LIB_EXT1_ _
    errno_t
    rsize_t
    int fwprintf_s(FILE * restrict stream,
         const wchar_t * restrict format, ...);
    int fwscanf_s(FILE * restrict stream,
         const wchar_t * restrict format, ...);
    int snwprintf_s(wchar_t * restrict s,
         rsize_t n,
         const wchar_t * restrict format, ...);
    int swprintf_s(wchar_t * restrict s, rsize_t n,
         const wchar_t * restrict format, ...);
    int swscanf_s(const wchar_t * restrict s,
         const wchar_t * restrict format, ...);
    int vfwprintf_s(FILE * restrict stream,
         const wchar_t * restrict format,
         va_list arg);
    int vfwscanf_s(FILE * restrict stream,
         const wchar_t * restrict format, va_list arg);
    int vsnwprintf_s(wchar_t * restrict s,
         rsize_t n,
         const wchar_t * restrict format,
         va_list arg);
    int vswprintf_s(wchar_t * restrict s,
         rsize_t n,
         const wchar_t * restrict format,
         va_list arg);
    int vswscanf_s(const wchar_t * restrict s,
         const wchar_t * restrict format,
         va_list arg);
    int vwprintf_s(const wchar_t * restrict format,
         va_list arg);
    int vwscanf_s(const wchar_t * restrict format,
         va_list arg);
    int wprintf_s(const wchar_t * restrict format, ...);
    int wscanf_s(const wchar_t * restrict format, ...);
    errno_t wcscpy_s(wchar_t * restrict s1,
         rsize_t s1max,
         const wchar_t * restrict s2);
    errno_t wcsncpy_s(wchar_t * restrict s1,
         rsize_t s1max,
         const wchar_t * restrict s2,
         rsize_t n);
    errno_t wmemcpy_s(wchar_t * restrict s1,
         rsize_t s1max,
         const wchar_t * restrict s2,
         rsize_t n);
    errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
         const wchar_t *s2, rsize_t n);
    errno_t wcscat_s(wchar_t * restrict s1,
         rsize_t s1max,
         const wchar_t * restrict s2);
    errno_t wcsncat_s(wchar_t * restrict s1,
         rsize_t s1max,
         const wchar_t * restrict s2,
         rsize_t n);
    wchar_t *wcstok_s(wchar_t * restrict s1,
         rsize_t * restrict s1max,
         const wchar_t * restrict s2,
         wchar_t ** restrict ptr);
    size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
    errno_t wcrtomb_s(size_t * restrict retval,
         char * restrict s, rsize_t smax,
         wchar_t wc, mbstate_t * restrict ps);
         errno_t mbsrtowcs_s(size_t * restrict retval,
              wchar_t * restrict dst, rsize_t dstmax,
              const char ** restrict src, rsize_t len,
              mbstate_t * restrict ps);
         errno_t wcsrtombs_s(size_t * restrict retval,
              char * restrict dst, rsize_t dstmax,
              const wchar_t ** restrict src, rsize_t len,
              mbstate_t * restrict ps);

### B.29 [Wide character classification and mapping utilities <wctype.h>]

    wint_t          wctrans_t      wctype_t        WEOF
         int iswalnum(wint_t wc);
         int iswalpha(wint_t wc);
         int iswblank(wint_t wc);
         int iswcntrl(wint_t wc);
         int iswdigit(wint_t wc);
         int iswgraph(wint_t wc);
         int iswlower(wint_t wc);
         int iswprint(wint_t wc);
         int iswpunct(wint_t wc);
         int iswspace(wint_t wc);
         int iswupper(wint_t wc);
         int iswxdigit(wint_t wc);
         int iswctype(wint_t wc, wctype_t desc);
         wctype_t wctype(const char *property);
         wint_t towlower(wint_t wc);
         wint_t towupper(wint_t wc);
         wint_t towctrans(wint_t wc, wctrans_t desc);
         wctrans_t wctrans(const char *property);

### C. [Annex C (informative) Sequence points]

    1   The following are the sequence points described in 5.1.2.3:
        — Between the evaluations of the function designator and actual arguments in a function
          call and the actual call. (6.5.2.2).
        — Between the evaluations of the first and second operands of the following operators:
          logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17).
        — Between the evaluations of the first operand of the conditional ? : operator and
          whichever of the second and third operands is evaluated (6.5.15).
        — The end of a full declarator: declarators (6.7.6);
        — Between the evaluation of a full expression and the next full expression to be
          evaluated. The following are full expressions: an initializer that is not part of a
          compound literal (6.7.9); the expression in an expression statement (6.8.3); the
          controlling expression of a selection statement (if or switch) (6.8.4); the
          controlling expression of a while or do statement (6.8.5); each of the (optional)
          expressions of a for statement (6.8.5.3); the (optional) expression in a return
          statement (6.8.6.4).
        — Immediately before a library function returns (7.1.4).
        — After the actions associated with each formatted input/output function conversion
          specifier (7.21.6, 7.29.2).
        — Immediately before and immediately after each call to a comparison function, and
          also between any call to a comparison function and any movement of the objects
          passed as arguments to that call (7.22.5).

### D. [Annex D (normative) Universal character names for identifiers]

    1   This clause lists the hexadecimal code values that are valid in universal character names
        in identifiers.

### D.1 [Ranges of characters allowed]

    1   00A8, 00AA, 00AD, 00AF, 00B2−00B5, 00B7−00BA, 00BC−00BE, 00C0−00D6,
        00D8−00F6, 00F8−00FF

    2   0100−167F, 1681−180D, 180F−1FFF

    3   200B−200D, 202A−202E, 203F−2040, 2054, 2060−206F

    4   2070−218F, 2460−24FF, 2776−2793, 2C00−2DFF, 2E80−2FFF

    5   3004−3007, 3021−302F, 3031−303F

    6   3040−D7FF

    7   F900−FD3D, FD40−FDCF, FDF0−FE44, FE47−FFFD

    8   10000−1FFFD, 20000−2FFFD, 30000−3FFFD, 40000−4FFFD, 50000−5FFFD,
        60000−6FFFD, 70000−7FFFD, 80000−8FFFD, 90000−9FFFD, A0000−AFFFD,
        B0000−BFFFD, C0000−CFFFD, D0000−DFFFD, E0000−EFFFD

### D.2 [Ranges of characters disallowed initially]

    1   0300−036F, 1DC0−1DFF, 20D0−20FF, FE20−FE2F

### E. [Annex E (informative) Implementation limits]

    1   The contents of the header <limits.h> are given below, in alphabetical order. The
        minimum magnitudes shown shall be replaced by implementation-defined magnitudes
        with the same sign. The values shall all be constant expressions suitable for use in #if
        preprocessing directives. The components are described further in 5.2.4.2.1.
               #define CHAR_BIT                                   8
               #define CHAR_MAX              UCHAR_MAX or SCHAR_MAX
               #define CHAR_MIN                      0 or SCHAR_MIN
               #define INT_MAX                               +32767
               #define INT_MIN                               -32767
               #define LONG_MAX                         +2147483647
               #define LONG_MIN                         -2147483647
               #define LLONG_MAX               +9223372036854775807
               #define LLONG_MIN               -9223372036854775807
               #define MB_LEN_MAX                                 1
               #define SCHAR_MAX                               +127
               #define SCHAR_MIN                               -127
               #define SHRT_MAX                              +32767
               #define SHRT_MIN                              -32767
               #define UCHAR_MAX                                255
               #define USHRT_MAX                              65535
               #define UINT_MAX                               65535
               #define ULONG_MAX                         4294967295
               #define ULLONG_MAX              18446744073709551615

    2   The contents of the header <float.h> are given below. All integer values, except
        FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing
        directives; all floating values shall be constant expressions. The components are
        described further in 5.2.4.2.2.

    3   The values given in the following list shall be replaced by implementation-defined
        expressions:
               #define FLT_EVAL_METHOD
               #define FLT_ROUNDS

    4   The values given in the following list shall be replaced by implementation-defined
        constant expressions that are greater or equal in magnitude (absolute value) to those
        shown, with the same sign:
               #define DLB_DECIMAL_DIG                                   10
               #define DBL_DIG                                           10
               #define DBL_MANT_DIG
               #define DBL_MAX_10_EXP                                  +37
               #define DBL_MAX_EXP
               #define DBL_MIN_10_EXP                                  -37
               #define DBL_MIN_EXP
               #define DECIMAL_DIG                                       10
               #define FLT_DECIMAL_DIG                                    6
               #define FLT_DIG                                            6
               #define FLT_MANT_DIG
               #define FLT_MAX_10_EXP                                  +37
               #define FLT_MAX_EXP
               #define FLT_MIN_10_EXP                                  -37
               #define FLT_MIN_EXP
               #define FLT_RADIX                                          2
               #define LDLB_DECIMAL_DIG                                  10
               #define LDBL_DIG                                          10
               #define LDBL_MANT_DIG
               #define LDBL_MAX_10_EXP                                 +37
               #define LDBL_MAX_EXP
               #define LDBL_MIN_10_EXP                                 -37
               #define LDBL_MIN_EXP

    5   The values given in the following list shall be replaced by implementation-defined
        constant expressions with values that are greater than or equal to those shown:
               #define DBL_MAX                                      1E+37
               #define FLT_MAX                                      1E+37
               #define LDBL_MAX                                     1E+37

    6   The values given in the following list shall be replaced by implementation-defined
        constant expressions with (positive) values that are less than or equal to those shown:
               #define DBL_EPSILON                                   1E-9
               #define DBL_MIN                                      1E-37
               #define FLT_EPSILON                                   1E-5
               #define FLT_MIN                                      1E-37
               #define LDBL_EPSILON                                  1E-9
               #define LDBL_MIN                                     1E-37

### F. [Annex F (normative) IEC 60559 floating-point arithmetic]

### F.1 [Introduction]

    1   This annex specifies C language support for the IEC 60559 floating-point standard. The
        IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for
        microprocessor systems, second edition (IEC 60559:1989), previously designated
        IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic
        (ANSI/IEEE 754−1985). IEEE Standard for Radix-Independent Floating-Point
        Arithmetic (ANSI/IEEE 854−1987) generalizes the binary standard to remove
        dependencies on radix and word length. IEC 60559 generally refers to the floating-point
        standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that
        defines _ _STDC_IEC_559_ _ shall conform to the specifications in this annex.[356]
        Where a binding between the C language and IEC 60559 is indicated, the
        IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since
        negative and positive infinity are representable in IEC 60559 formats, all real numbers lie
        within the range of representable values.

    Footnote 356) Implementations that do not define _ _STDC_IEC_559_ _ are not required to conform to these
             specifications.

### F.2 [Types]

    1   The C floating types match the IEC 60559 formats as follows:
        — The float type matches the IEC 60559 single format.
        — The double type matches the IEC 60559 double format.
        — The long double type matches an IEC 60559 extended format,[357] else a
          non-IEC 60559 extended format, else the IEC 60559 double format.
        Any non-IEC 60559 extended format used for the long double type shall have more
        precision than IEC 60559 double and at least the range of IEC 60559 double.[358]
        Recommended practice

    Footnote 357) ‘‘Extended’’ is IEC 60559’s double-extended data format. Extended refers to both the common 80-bit
             and quadruple 128-bit IEC 60559 formats.

    Footnote 358) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include
             all double values.

    2   The long double type should match an IEC 60559 extended format.

### F.2.1 [Infinities, signed zeros, and NaNs]

    1   This specification does not define the behavior of signaling NaNs.[359] It generally uses
        the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan
        functions in <math.h> provide designations for IEC 60559 NaNs and infinities.

    Footnote 359) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are
             sufficient for closure of the arithmetic.

### F.3 [Operators and functions]

    1   C operators and functions provide IEC 60559 required and recommended facilities as
        listed below.
        — The +, −, *, and / operators provide the IEC 60559 add, subtract, multiply, and
          divide operations.
        — The sqrt functions in <math.h> provide the IEC 60559 square root operation.
        — The remainder functions in <math.h> provide the IEC 60559 remainder
          operation. The remquo functions in <math.h> provide the same operation but
          with additional information.
        — The rint functions in <math.h> provide the IEC 60559 operation that rounds a
          floating-point number to an integer value (in the same precision). The nearbyint
          functions in <math.h> provide the nearbyinteger function recommended in the
          Appendix to ANSI/IEEE 854.
        — The conversions for floating types provide the IEC 60559 conversions between
          floating-point precisions.
        — The conversions from integer to floating types provide the IEC 60559 conversions
          from integer to floating point.
        — The conversions from floating to integer types provide IEC 60559-like conversions
          but always round toward zero.
        — The lrint and llrint functions in <math.h> provide the IEC 60559
          conversions, which honor the directed rounding mode, from floating point to the
          long int and long long int integer formats. The lrint and llrint
          functions can be used to implement IEC 60559 conversions from floating to other
          integer formats.
        — The translation time conversion of floating constants and the strtod, strtof,
          strtold, fprintf, fscanf, and related library functions in <stdlib.h>,
       <stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The
       strtold function in <stdlib.h> provides the conv function recommended in the
       Appendix to ANSI/IEEE 854.
    — The relational and equality operators provide IEC 60559 comparisons. IEC 60559
      identifies a need for additional comparison predicates to facilitate writing code that
      accounts for NaNs. The comparison macros (isgreater, isgreaterequal,
      isless, islessequal, islessgreater, and isunordered) in <math.h>
      supplement the language operators to address this need. The islessgreater and
      isunordered macros provide respectively a quiet version of the <> predicate and
      the unordered predicate recommended in the Appendix to IEC 60559.
    — The feclearexcept, feraiseexcept, and fetestexcept functions in
      <fenv.h> provide the facility to test and alter the IEC 60559 floating-point
      exception status flags. The fegetexceptflag and fesetexceptflag
      functions in <fenv.h> provide the facility to save and restore all five status flags at
      one time. These functions are used in conjunction with the type fexcept_t and the
      floating-point    exception      macros      (FE_INEXACT,         FE_DIVBYZERO,
      FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>.
    — The fegetround and fesetround functions in <fenv.h> provide the facility
      to select among the IEC 60559 directed rounding modes represented by the rounding
      direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
      FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the
      IEC 60559 directed rounding modes.
    — The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in
      <fenv.h> provide a facility to manage the floating-point environment, comprising
      the IEC 60559 status flags and control modes.
    — The copysign functions in <math.h> provide the copysign function
      recommended in the Appendix to IEC 60559.
    — The fabs functions in <math.h> provide the abs function recommended in the
      Appendix to IEC 60559.
    — The unary minus (−) operator provides the unary minus (−) operation recommended
      in the Appendix to IEC 60559.
    — The scalbn and scalbln functions in <math.h> provide the scalb function
      recommended in the Appendix to IEC 60559.
    — The logb functions in <math.h> provide the logb function recommended in the
      Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854.
    — The nextafter and nexttoward functions in <math.h> provide the nextafter
      function recommended in the Appendix to IEC 60559 (but with a minor change to
            better handle signed zeros).
        — The isfinite macro in <math.h> provides the finite function recommended in
          the Appendix to IEC 60559.
        — The isnan macro in <math.h> provides the isnan function recommended in the
          Appendix to IEC 60559.
        — The signbit macro and the fpclassify macro in <math.h>, used in
          conjunction with the number classification macros (FP_NAN, FP_INFINITE,
          FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class
          function recommended in the Appendix to IEC 60559 (except that the classification
          macros defined in 7.12.3 do not distinguish signaling from quiet NaNs).

### F.4 [Floating to integer conversion]

    1   If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised
        (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part
        of the floating value exceeds the range of the integer type, then the ‘‘invalid’’ floating-
        point exception is raised and the resulting value is unspecified. Otherwise, the resulting
        value is determined by 6.3.1.4. Conversion of an integral floating value that does not
        exceed the range of the integer type raises no floating-point exceptions; whether
        conversion of a non-integral floating value raises the ‘‘inexact’’ floating-point exception is
        unspecified.[360]

    Footnote 360) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer
             conversions raise the ‘‘inexact’’ floating-point exception for non-integer in-range values. In those
             cases where it matters, library functions can be used to effect such conversions with or without raising
             the ‘‘inexact’’ floating-point exception. See rint, lrint, llrint, and nearbyint in
             <math.h>.

### F.5 [Binary-decimal conversion]

    1   Conversion from the widest supported IEC 60559 format to decimal with
        DECIMAL_DIG digits and back is the identity function.[361]

    Footnote 361) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported,
             DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest
             IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and
             DBL_DIG are 18 and 15, respectively, for these formats.)

    2   Conversions involving IEC 60559 formats follow all pertinent recommended practice. In
        particular, conversion between any supported IEC 60559 format and decimal with
        DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current
        rounding mode), which assures that conversion from the widest supported IEC 60559
        format to decimal with DECIMAL_DIG digits and back is the identity function.

    3   Functions such as strtod that convert character sequences to floating types honor the
        rounding direction. Hence, if the rounding direction might be upward or downward, the
        implementation cannot convert a minus-signed sequence by negating the converted
        unsigned sequence.

### F.6 [The return statement]

    If the return expression is evaluated in a floating-point format different from the return
        type, the expression is converted as if by assignment[362] to the return type of the function
        and the resulting value is returned to the caller.

    Footnote 362) Assignment removes any extra range and precision.

### F.7 [Contracted expressions]

    1   A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed
        zeros, subnormals, and the rounding directions in a manner consistent with the basic
        arithmetic operations covered by IEC 60559.
        Recommended practice

    2   A contracted expression should raise floating-point exceptions in a manner generally
        consistent with the basic arithmetic operations.

### F.8 [Floating-point environment]

    1   The floating-point environment defined in <fenv.h> includes the IEC 60559 floating-
        point exception status flags and directed-rounding control modes. It includes also
        IEC 60559 dynamic rounding precision and trap enablement modes, if the
        implementation supports them.[363]

    Footnote 363) This specification does not require dynamic rounding precision nor trap enablement modes.

### F.8.1 [Environment management]

    1   IEC 60559 requires that floating-point operations implicitly raise floating-point exception
        status flags, and that rounding control modes can be set explicitly to affect result values of
        floating-point operations. When the state for the FENV_ACCESS pragma (defined in
        <fenv.h>) is ‘‘on’’, these changes to the floating-point state are treated as side effects
        which respect sequence points.[364]

    Footnote 364) If the state for the FENV_ACCESS pragma is ‘‘off’’, the implementation is free to assume the floating-
             point control modes will be the default ones and the floating-point status flags will not be tested,
             which allows certain optimizations (see F.9).

### F.8.2 [Translation]

    1   During translation the IEC 60559 default modes are in effect:
        — The rounding direction mode is rounding to nearest.
        — The rounding precision mode (if supported) is set so that results are not shortened.
        — Trapping or stopping (if supported) is disabled on all floating-point exceptions.
        Recommended practice

    2   The implementation should produce a diagnostic message for each translation-time
        floating-point exception, other than ‘‘inexact’’;[365] the implementation should then
        proceed with the translation of the program.

    Footnote 365) As floating constants are converted to appropriate internal representations at translation time, their
             conversion is subject to default rounding modes and raises no execution-time floating-point exceptions
             (even where the state of the FENV_ACCESS pragma is ‘‘on’’). Library functions, for example
             strtod, provide execution-time conversion of numeric strings.

### F.8.3 [Execution]

    1   At program startup the floating-point environment is initialized as prescribed by
        IEC 60559:
        — All floating-point exception status flags are cleared.
        — The rounding direction mode is rounding to nearest.
        — The dynamic rounding precision mode (if supported) is set so that results are not
          shortened.
        — Trapping or stopping (if supported) is disabled on all floating-point exceptions.

### F.8.4 [Constant expressions]

    1   An arithmetic constant expression of floating type, other than one in an initializer for an
        object that has static or thread storage duration, is evaluated (as if) during execution; thus,
        it is affected by any operative floating-point control modes and raises floating-point
        exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma
        is ‘‘on’’).[366]

    Footnote 366) Where the state for the FENV_ACCESS pragma is ‘‘on’’, results of inexact expressions like 1.0/3.0
             are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
             1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the
             efficiency of translation-time evaluation through static initialization, such as
                      const static double one_third = 1.0/3.0;

    2   EXAMPLE
                 #include <fenv.h>
                 #pragma STDC FENV_ACCESS ON
                 void f(void)
                 {
                       float w[] = { 0.0/0.0 }; // raises an exception
                       static float x = 0.0/0.0; // does not raise an exception
                       float y = 0.0/0.0;        // raises an exception
                       double z = 0.0/0.0;       // raises an exception
                       /* ... */
                 }

    3   For the static initialization, the division is done at translation time, raising no (execution-time) floating-
        point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at
        execution time.

### F.8.5 [Initialization]

    1   All computation for automatic initialization is done (as if) at execution time; thus, it is
        affected by any operative modes and raises floating-point exceptions as required by
        IEC 60559 (provided the state for the FENV_ACCESS pragma is ‘‘on’’). All computation
        for initialization of objects that have static or thread storage duration is done (as if) at
        translation time.

    2   EXAMPLE
                 #include <fenv.h>
                 #pragma STDC FENV_ACCESS ON
                 void f(void)
                 {
                       float u[] = { 1.1e75 }; // raises exceptions
                       static float v = 1.1e75; // does not raise exceptions
                       float w = 1.1e75;        // raises exceptions
                       double x = 1.1e75;       // may raise exceptions
                       float y = 1.1e75f;       // may raise exceptions
                       long double z = 1.1e75; // does not raise exceptions
                       /* ... */
                 }

    3   The static initialization of v raises no (execution-time) floating-point exceptions because its computation is
        done at translation time. The automatic initialization of u and w require an execution-time conversion to
        float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations
        of x and y entail execution-time conversion; however, in some expression evaluation methods, the
        conversions is not to a narrower format, in which case no floating-point exception is raised.[367] The
        automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating-
        point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to
        their internal representations occur at translation time in all cases.

    Footnote 367) Use of float_t and double_t variables increases the likelihood of translation-time computation.
             For example, the automatic initialization
                      double_t x = 1.1e75;
             could be done at translation time, regardless of the expression evaluation method.

### F.8.6 [Changing the environment]

    1   Operations defined in 6.5 and functions and macros defined for the standard libraries
        change floating-point status flags and control modes just as indicated by their
        specifications (including conformance to IEC 60559). They do not change flags or modes
        (so as to be detectable by the user) in any other cases.

    2   If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559
        valid coincident floating-point exceptions for atomic operations (namely ‘‘overflow’’ and
        ‘‘inexact’’, or ‘‘underflow’’ and ‘‘inexact’’), then ‘‘overflow’’ or ‘‘underflow’’ is raised
        before ‘‘inexact’’.

### F.9 [Optimization]

    1   This section identifies code transformations that might subvert IEC 60559-specified
        behavior, and others that do not.

### F.9.1 [Global transformations]

    1   Floating-point arithmetic operations and external function calls may entail side effects
        which optimization shall honor, at least where the state of the FENV_ACCESS pragma is
        ‘‘on’’. The flags and modes in the floating-point environment may be regarded as global
        variables; floating-point operations (+, *, etc.) implicitly read the modes and write the
        flags.

    2   Concern about side effects may inhibit code motion and removal of seemingly useless
        code. For example, in
                 #include <fenv.h>
                 #pragma STDC FENV_ACCESS ON
                 void f(double x)
                 {
                      /* ... */
                      for (i = 0; i < n; i++) x + 1;
                      /* ... */
                 }
        x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop
        body might not execute (maybe 0 ≥ n), x + 1 cannot be moved out of the loop. (Of
        course these optimizations are valid if the implementation can rule out the nettlesome
        cases.)

    3   This specification does not require support for trap handlers that maintain information
        about the order or count of floating-point exceptions. Therefore, between function calls,
        floating-point exceptions need not be precise: the actual order and number of occurrences
        of floating-point exceptions (> 1) may vary from what the source code expresses. Thus,
        the preceding loop could be treated as
                if (0 < n) x + 1;

### F.9.2 [Expression transformations]

    1   x/2 ↔ x × 0.5          Although similar transformations involving inexact constants
                               generally do not yield numerically equivalent expressions, if the
                               constants are exact then such transformations can be made on
                               IEC 60559 machines and others that round perfectly.
        1 × x and x/1 → x The expressions 1 × x, x/1, and x are equivalent (on IEC 60559
                          machines, among others).[368]
        x/x → 1. 0             The expressions x/x and 1. 0 are not equivalent if x can be zero,
                               infinite, or NaN.
        x − y ↔ x + (−y)       The expressions x − y, x + (−y), and (−y) + x are equivalent (on
                               IEC 60559 machines, among others).
        x − y ↔ −(y − x)       The expressions x − y and −(y − x) are not equivalent because 1 − 1
                               is +0 but −(1 − 1) is −0 (in the default rounding direction).[369]
        x − x → 0. 0           The expressions x − x and 0. 0 are not equivalent if x is a NaN or
                               infinite.
        0 × x → 0. 0           The expressions 0 × x and 0. 0 are not equivalent if x is a NaN,
                               infinite, or −0.
        x+0→ x                 The expressions x + 0 and x are not equivalent if x is −0, because
                               (−0) + (+0) yields +0 (in the default rounding direction), not −0.
        x−0→ x                 (+0) − (+0) yields −0 when rounding is downward (toward −∞), but
                               +0 otherwise, and (−0) − (+0) always yields −0; so, if the state of the
                               FENV_ACCESS pragma is ‘‘off’’, promising default rounding, then
                               the implementation can replace x − 0 by x, even if x might be zero.
        −x ↔ 0 − x             The expressions −x and 0 − x are not equivalent if x is +0, because
                               −(+0) yields −0, but 0 − (+0) yields +0 (unless rounding is
                               downward).

    Footnote 368) Strict support for signaling NaNs — not required by this specification — would invalidate these and
             other transformations that remove arithmetic operators.

    Footnote 369) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
             Examples include:
                1/(1/ ± ∞) is ± ∞
             and
                conj(csqrt(z)) is csqrt(conj(z)),
             for complex z.

### F.9.3 [Relational operators]

    1   x ≠ x → false           The expression x ≠ x is true if x is a NaN.
        x = x → true            The expression x = x is false if x is a NaN.
        x < y → isless(x,y) (and similarly for ≤, >, ≥) Though numerically equal, these
                       expressions are not equivalent because of side effects when x or y is a
                       NaN and the state of the FENV_ACCESS pragma is ‘‘on’’. This
                       transformation, which would be desirable if extra code were required
                       to cause the ‘‘invalid’’ floating-point exception for unordered cases,
                       could be performed provided the state of the FENV_ACCESS pragma
                       is ‘‘off’’.
        The sense of relational operators shall be maintained. This includes handling unordered
        cases as expressed by the source code.

    2   EXAMPLE
                 // calls g and raises ‘‘invalid’’ if a and b are unordered
                 if (a < b)
                         f();
                 else
                         g();
        is not equivalent to
                 // calls f and raises ‘‘invalid’’ if a and b are unordered
                 if (a >= b)
                         g();
                 else
                         f();
        nor to
                 // calls f without raising ‘‘invalid’’ if a and b are unordered
                 if (isgreaterequal(a,b))
                         g();
                 else
                         f();
        nor, unless the state of the FENV_ACCESS pragma is ‘‘off’’, to
                 // calls g without raising ‘‘invalid’’ if a and b are unordered
                 if (isless(a,b))
                         f();
                 else
                         g();
        but is equivalent to
                if (!(a < b))
                      g();
                else
                      f();

### F.9.4 [Constant arithmetic]

    1   The implementation shall honor floating-point exceptions raised by execution-time
        constant arithmetic wherever the state of the FENV_ACCESS pragma is ‘‘on’’. (See F.8.4
        and F.8.5.) An operation on constants that raises no floating-point exception can be
        folded during translation, except, if the state of the FENV_ACCESS pragma is ‘‘on’’, a
        further check is required to assure that changing the rounding direction to downward does
        not alter the sign of the result,[370] and implementations that support dynamic rounding
        precision modes shall assure further that the result of the operation raises no floating-
        point exception when converted to the semantic type of the operation.

    Footnote 370) 0 − 0 yields −0 instead of +0 just when the rounding direction is downward.

### F.10 [Mathematics <math.h>]

    1   This subclause contains specifications of <math.h> facilities that are particularly suited
        for IEC 60559 implementations.

    2   The Standard C macro HUGE_VAL and its float and long double analogs,
        HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive
        infinities.

    3   Special cases for functions in <math.h> are covered directly or indirectly by
        IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The
        other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and
        (provided the state of the FENV_ACCESS pragma is ‘‘on’’) the floating-point status flags
        in a manner consistent with the basic arithmetic operations covered by IEC 60559.

    4   The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a
        nonzero value.

    5   The ‘‘invalid’’ and ‘‘divide-by-zero’’ floating-point exceptions are raised as specified in
        subsequent subclauses of this annex.

    6   The ‘‘overflow’’ floating-point exception is raised whenever an infinity — or, because of
        rounding direction, a maximal-magnitude finite number — is returned in lieu of a value
        whose magnitude is too large.

    7   The ‘‘underflow’’ floating-point exception is raised whenever a result is tiny (essentially
        subnormal or zero) and suffers loss of accuracy.[371]

    Footnote 371) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on
             when the floating-point exception is raised.

    8    Whether or when library functions raise the ‘‘inexact’’ floating-point exception is
         unspecified, unless explicitly specified otherwise.

    9    Whether or when library functions raise an undeserved ‘‘underflow’’ floating-point
         exception is unspecified.[372] Otherwise, as implied by F.8.6, the <math.h> functions do
         not raise spurious floating-point exceptions (detectable by the user), other than the
         ‘‘inexact’’ floating-point exception.

    Footnote 372) It is intended that undeserved ‘‘underflow’’ and ‘‘inexact’’ floating-point exceptions are raised only if
              avoiding them would be too costly.

    10   Whether the functions honor the rounding direction mode is implementation-defined,
         unless explicitly specified otherwise.

    11   Functions with a NaN argument return a NaN result and raise no floating-point exception,
         except where stated otherwise.

    12   The specifications in the following subclauses append to the definitions in <math.h>.
         For families of functions, the specifications apply to all of the functions even though only
         the principal function is shown. Unless otherwise specified, where the symbol ‘‘±’’
         occurs in both an argument and the result, the result has the same sign as the argument.
         Recommended practice

    13   If a function with one or more NaN arguments returns a NaN result, the result should be
         the same as one of the NaN arguments (after possible type conversion), except perhaps
         for the sign.

### F.10.1 [Trigonometric functions]

### F.10.1.1 [The acos functions]

    1    — acos(1) returns +0.
         — acos(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for
           | x | > 1.

### F.10.1.2 [The asin functions]

    1    — asin(±0) returns ±0.
         — asin(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for
           | x | > 1.

### F.10.1.3 [The atan functions]

    1   — atan(±0) returns ±0.
        — atan(±∞) returns ±π /2.

### F.10.1.4 [The atan2 functions]

    1   — atan2(±0, −0) returns ±π .[373]
        — atan2(±0, +0) returns ±0.
        — atan2(±0, x) returns ±π for x < 0.
        — atan2(±0, x) returns ±0 for x > 0.
        — atan2(y, ±0) returns −π /2 for y < 0.
        — atan2(y, ±0) returns π /2 for y > 0.
        — atan2(±y, −∞) returns ±π for finite y > 0.
        — atan2(±y, +∞) returns ±0 for finite y > 0.
        — atan2(±∞, x) returns ±π /2 for finite x.
        — atan2(±∞, −∞) returns ±3π /4.
        — atan2(±∞, +∞) returns ±π /4.

    Footnote 373) atan2(0, 0) does not raise the ‘‘invalid’’ floating-point exception, nor does atan2( y , 0) raise
             the ‘‘divide-by-zero’’ floating-point exception.

### F.10.1.5 [The cos functions]

    1   — cos(±0) returns 1.
        — cos(±∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.

### F.10.1.6 [The sin functions]

    1   — sin(±0) returns ±0.
        — sin(±∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.

### F.10.1.7 [The tan functions]

    1   — tan(±0) returns ±0.
        — tan(±∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.

### F.10.2 [Hyperbolic functions]

### F.10.2.1 [The acosh functions]

    1   — acosh(1) returns +0.
        — acosh(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 1.
        — acosh(+∞) returns +∞.

### F.10.2.2 [The asinh functions]

    1   — asinh(±0) returns ±0.
        — asinh(±∞) returns ±∞.

### F.10.2.3 [The atanh functions]

    1   — atanh(±0) returns ±0.
        — atanh(±1) returns ±∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — atanh(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for
          | x | > 1.

### F.10.2.4 [The cosh functions]

    1   — cosh(±0) returns 1.
        — cosh(±∞) returns +∞.

### F.10.2.5 [The sinh functions]

    1   — sinh(±0) returns ±0.
        — sinh(±∞) returns ±∞.

### F.10.2.6 [The tanh functions]

    1   — tanh(±0) returns ±0.
        — tanh(±∞) returns ±1.

### F.10.3 [Exponential and logarithmic functions]

### F.10.3.1 [The exp functions]

    1   — exp(±0) returns 1.
        — exp(−∞) returns +0.
        — exp(+∞) returns +∞.

### F.10.3.2 [The exp2 functions]

    1   — exp2(±0) returns 1.
        — exp2(−∞) returns +0.
        — exp2(+∞) returns +∞.

### F.10.3.3 [The expm1 functions]

    1   — expm1(±0) returns ±0.
        — expm1(−∞) returns −1.
        — expm1(+∞) returns +∞.

### F.10.3.4 [The frexp functions]

    1   — frexp(±0, exp) returns ±0, and stores 0 in the object pointed to by exp.
        — frexp(±∞, exp) returns ±∞, and stores an unspecified value in the object
          pointed to by exp.
        — frexp(NaN, exp) stores an unspecified value in the object pointed to by exp
          (and returns a NaN).

    2   frexp raises no floating-point exceptions.

    3   When the radix of the argument is a power of 2, the returned value is exact and is
        independent of the current rounding direction mode.

    4   On a binary system, the body of the frexp function might be
               {
                       *exp = (value == 0) ? 0 : (int)(1 + logb(value));
                       return scalbn(value, -(*exp));
               }

### F.10.3.5 [The ilogb functions]

    1   When the correct result is representable in the range of the return type, the returned value
        is exact and is independent of the current rounding direction mode.

    2   If the correct result is outside the range of the return type, the numeric result is
        unspecified and the ‘‘invalid’’ floating-point exception is raised.

    3   ilogb(x), for x zero, infinite, or NaN, raises the ‘‘invalid’’ floating-point exception and
        returns the value specified in 7.12.6.5.

### F.10.3.6 [The ldexp functions]

    1   On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).

### F.10.3.7 [The log functions]

    1   — log(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — log(1) returns +0.
        — log(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 0.
        — log(+∞) returns +∞.

### F.10.3.8 [The log10 functions]

    1   — log10(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — log10(1) returns +0.
        — log10(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 0.
        — log10(+∞) returns +∞.

### F.10.3.9 [The log1p functions]

    1   — log1p(±0) returns ±0.
        — log1p(−1) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — log1p(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for
          x < −1.
        — log1p(+∞) returns +∞.

### F.10.3.10 [The log2 functions]

    1   — log2(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — log2(1) returns +0.
        — log2(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x < 0.
        — log2(+∞) returns +∞.

### F.10.3.11 [The logb functions]

    1   — logb(±0) returns −∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — logb(±∞) returns +∞.

    2   The returned value is exact and is independent of the current rounding direction mode.

### F.10.3.12 [The modf functions]

    1   — modf(±x, iptr) returns a result with the same sign as x.
        — modf(±∞, iptr) returns ±0 and stores ±∞ in the object pointed to by iptr.
        — modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a
          NaN).

    2   The returned values are exact and are independent of the current rounding direction
        mode.

    3   modf behaves as though implemented by
              #include <math.h>
              #include <fenv.h>
              #pragma STDC FENV_ACCESS ON
              double modf(double value, double *iptr)
              {
                   int save_round = fegetround();
                   fesetround(FE_TOWARDZERO);
                   *iptr = nearbyint(value);
                   fesetround(save_round);
                   return copysign(
                        isinf(value) ? 0.0 :
                             value - (*iptr), value);
              }

### F.10.3.13 [The scalbn and scalbln functions]

    1   — scalbn(±0, n) returns ±0.
        — scalbn(x, 0) returns x.
        — scalbn(±∞, n) returns ±∞.

    2   If the calculation does not overflow or underflow, the returned value is exact and
        independent of the current rounding direction mode.

### F.10.4 [Power and absolute value functions]

### F.10.4.1 [The cbrt functions]

    1   — cbrt(±0) returns ±0.
        — cbrt(±∞) returns ±∞.

### F.10.4.2 [The fabs functions]

    1   — fabs(±0) returns +0.
        — fabs(±∞) returns +∞.

    2   The returned value is exact and is independent of the current rounding direction mode.

### F.10.4.3 [The hypot functions]

    1   — hypot(x, y), hypot(y, x), and hypot(x, −y) are equivalent.
        — hypot(x, ±0) is equivalent to fabs(x).
        — hypot(±∞, y) returns +∞, even if y is a NaN.

### F.10.4.4 [The pow functions]

    1   — pow(±0, y) returns ±∞ and raises the ‘‘divide-by-zero’’ floating-point exception
          for y an odd integer < 0.
        — pow(±0, y) returns +∞ and raises the ‘‘divide-by-zero’’ floating-point exception
          for y < 0, finite, and not an odd integer.
        — pow(±0, −∞) returns +∞ and may raise the ‘‘divide-by-zero’’ floating-point
          exception.
        — pow(±0, y) returns ±0 for y an odd integer > 0.
        — pow(±0, y) returns +0 for y > 0 and not an odd integer.
        — pow(−1, ±∞) returns 1.
        — pow(+1, y) returns 1 for any y, even a NaN.
        — pow(x, ±0) returns 1 for any x, even a NaN.
        — pow(x, y) returns a NaN and raises the ‘‘invalid’’ floating-point exception for
          finite x < 0 and finite non-integer y.
        — pow(x, −∞) returns +∞ for | x | < 1.
        — pow(x, −∞) returns +0 for | x | > 1.
        — pow(x, +∞) returns +0 for | x | < 1.
        — pow(x, +∞) returns +∞ for | x | > 1.
        — pow(−∞, y) returns −0 for y an odd integer < 0.
        — pow(−∞, y) returns +0 for y < 0 and not an odd integer.
        — pow(−∞, y) returns −∞ for y an odd integer > 0.
        — pow(−∞, y) returns +∞ for y > 0 and not an odd integer.
        — pow(+∞, y) returns +0 for y < 0.
        — pow(+∞, y) returns +∞ for y > 0.

### F.10.4.5 [The sqrt functions]

    1   sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value
        is dependent on the current rounding direction mode.

### F.10.5 [Error and gamma functions]

### F.10.5.1 [The erf functions]

    1   — erf(±0) returns ±0.
        — erf(±∞) returns ±1.

### F.10.5.2 [The erfc functions]

    1   — erfc(−∞) returns 2.
        — erfc(+∞) returns +0.

### F.10.5.3 [The lgamma functions]

    1   — lgamma(1) returns +0.
        — lgamma(2) returns +0.
        — lgamma(x) returns +∞ and raises the ‘‘divide-by-zero’’ floating-point exception for
          x a negative integer or zero.
        — lgamma(−∞) returns +∞.
        — lgamma(+∞) returns +∞.

### F.10.5.4 [The tgamma functions]

    1   — tgamma(±0) returns ±∞ and raises the ‘‘divide-by-zero’’ floating-point exception.
        — tgamma(x) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x a
          negative integer.
        — tgamma(−∞) returns a NaN and raises the ‘‘invalid’’ floating-point exception.
        — tgamma(+∞) returns +∞.

### F.10.6 [Nearest integer functions]

### F.10.6.1 [The ceil functions]

    1   — ceil(±0) returns ±0.
        — ceil(±∞) returns ±∞.

    2   The returned value is independent of the current rounding direction mode.

    3   The double version of ceil behaves as though implemented by
               #include <math.h>
               #include <fenv.h>
               #pragma STDC FENV_ACCESS ON
               double ceil(double x)
               {
                    double result;
                    int save_round = fegetround();
                    fesetround(FE_UPWARD);
                    result = rint(x); // or nearbyint instead of rint
                    fesetround(save_round);
                    return result;
               }

    4   The ceil functions may, but are not required to, raise the ‘‘inexact’’ floating-point
        exception for finite non-integer arguments, as this implementation does.

### F.10.6.2 [The floor functions]

    1   — floor(±0) returns ±0.
        — floor(±∞) returns ±∞.

    2   The returned value and is independent of the current rounding direction mode.

    3   See the sample implementation for ceil in F.10.6.1. The floor functions may, but are
        not required to, raise the ‘‘inexact’’ floating-point exception for finite non-integer
        arguments, as that implementation does.

### F.10.6.3 [The nearbyint functions]

    1   The nearbyint functions use IEC 60559 rounding according to the current rounding
        direction. They do not raise the ‘‘inexact’’ floating-point exception if the result differs in
        value from the argument.
        — nearbyint(±0) returns ±0 (for all rounding directions).
        — nearbyint(±∞) returns ±∞ (for all rounding directions).

### F.10.6.4 [The rint functions]

    1   The rint functions differ from the nearbyint functions only in that they do raise the
        ‘‘inexact’’ floating-point exception if the result differs in value from the argument.

### F.10.6.5 [The lrint and llrint functions]

    1   The lrint and llrint functions provide floating-to-integer conversion as prescribed
        by IEC 60559. They round according to the current rounding direction. If the rounded
        value is outside the range of the return type, the numeric result is unspecified and the
        ‘‘invalid’’ floating-point exception is raised. When they raise no other floating-point
        exception and the result differs from the argument, they raise the ‘‘inexact’’ floating-point
        exception.

### F.10.6.6 [The round functions]

    1   — round(±0) returns ±0.
        — round(±∞) returns ±∞.

    2   The returned value is independent of the current rounding direction mode.

    3   The double version of round behaves as though implemented by
               #include <math.h>
               #include <fenv.h>
               #pragma STDC FENV_ACCESS ON
               double round(double x)
               {
                    double result;
                    fenv_t save_env;
                    feholdexcept(&save_env);
                    result = rint(x);
                    if (fetestexcept(FE_INEXACT)) {
                         fesetround(FE_TOWARDZERO);
                         result = rint(copysign(0.5 + fabs(x), x));
                    }
                    feupdateenv(&save_env);
                    return result;
               }
        The round functions may, but are not required to, raise the ‘‘inexact’’ floating-point
        exception for finite non-integer numeric arguments, as this implementation does.

### F.10.6.7 [The lround and llround functions]

    1   The lround and llround functions differ from the lrint and llrint functions
        with the default rounding direction just in that the lround and llround functions
        round halfway cases away from zero and need not raise the ‘‘inexact’’ floating-point
        exception for non-integer arguments that round to within the range of the return type.

### F.10.6.8 [The trunc functions]

    1   The trunc functions use IEC 60559 rounding toward zero (regardless of the current
        rounding direction). The returned value is exact.
        — trunc(±0) returns ±0.
        — trunc(±∞) returns ±∞.

    2   The returned value is independent of the current rounding direction mode. The trunc
        functions may, but are not required to, raise the ‘‘inexact’’ floating-point exception for
        finite non-integer arguments.

### F.10.7 [Remainder functions]

### F.10.7.1 [The fmod functions]

    1   — fmod(±0, y) returns ±0 for y not zero.
        — fmod(x, y) returns a NaN and raises the ‘‘invalid’’ floating-point exception for x
          infinite or y zero (and neither is a NaN).
        — fmod(x, ±∞) returns x for x not infinite.

    2   When subnormal results are supported, the returned value is exact and is independent of
        the current rounding direction mode.

    3   The double version of fmod behaves as though implemented by
               #include <math.h>
               #include <fenv.h>
               #pragma STDC FENV_ACCESS ON
               double fmod(double x, double y)
               {
                    double result;
                    result = remainder(fabs(x), (y = fabs(y)));
                    if (signbit(result)) result += y;
                    return copysign(result, x);
               }

### F.10.7.2 [The remainder functions]

    1   The remainder functions are fully specified as a basic arithmetic operation in
        IEC 60559.

    2   When subnormal results are supported, the returned value is exact and is independent of
        the current rounding direction mode.

### F.10.7.3 [The remquo functions]

    1   The remquo functions follow the specifications for the remainder functions. They
        have no further specifications special to IEC 60559 implementations.

    2   When subnormal results are supported, the returned value is exact and is independent of
        the current rounding direction mode.

### F.10.8 [Manipulation functions]

### F.10.8.1 [The copysign functions]

    1   copysign is specified in the Appendix to IEC 60559.

    2   The returned value is exact and is independent of the current rounding direction mode.

### F.10.8.2 [The nan functions]

    1   All IEC 60559 implementations support quiet NaNs, in all floating formats.

    2   The returned value is exact and is independent of the current rounding direction mode.

### F.10.8.3 [The nextafter functions]

    1   — nextafter(x, y) raises the ‘‘overflow’’ and ‘‘inexact’’ floating-point exceptions
          for x finite and the function value infinite.
        — nextafter(x, y) raises the ‘‘underflow’’ and ‘‘inexact’’ floating-point
          exceptions for the function value subnormal or zero and x ≠ y.

    2   Even though underflow or overflow can occur, the returned value is independent of the
        current rounding direction mode.

### F.10.8.4 [The nexttoward functions]

    1   No additional requirements beyond those on nextafter.

    2   Even though underflow or overflow can occur, the returned value is independent of the
        current rounding direction mode.

### F.10.9 [Maximum, minimum, and positive difference functions]

### F.10.9.1 [The fdim functions]

    1   No additional requirements.

### F.10.9.2 [The fmax functions]

    1   If just one argument is a NaN, the fmax functions return the other argument (if both
        arguments are NaNs, the functions return a NaN).

    2   The returned value is exact and is independent of the current rounding direction mode.

    3   The body of the fmax function might be[374]
                { return (isgreaterequal(x, y) ||
                     isnan(y)) ? x : y; }

    Footnote 374) Ideally, fmax would be sensitive to the sign of zero, for example fmax(−0. 0,   +0. 0) would
             return +0; however, implementation in software might be impractical.

### F.10.9.3 [The fmin functions]

    1   The fmin functions are analogous to the fmax functions (see F.10.9.2).

    2   The returned value is exact and is independent of the current rounding direction mode.

### F.10.10 [Floating multiply-add]

### F.10.10.1 [The fma functions]

    1   — fma(x, y, z) computes xy + z, correctly rounded once.
        — fma(x, y, z) returns a NaN and optionally raises the ‘‘invalid’’ floating-point
          exception if one of x and y is infinite, the other is zero, and z is a NaN.
        — fma(x, y, z) returns a NaN and raises the ‘‘invalid’’ floating-point exception if
          one of x and y is infinite, the other is zero, and z is not a NaN.
        — fma(x, y, z) returns a NaN and raises the ‘‘invalid’’ floating-point exception if x
          times y is an exact infinity and z is also an infinity but with the opposite sign.

### F.10.11 [Comparison macros]

    1   Relational operators and their corresponding comparison macros (7.12.14) produce
        equivalent result values, even if argument values are represented in wider formats. Thus,
        comparison macro arguments represented in formats wider than their semantic types are
        not converted to the semantic types, unless the wide evaluation method converts operands
        of relational operators to their semantic types. The standard wide evaluation methods
        characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert
        operands of relational operators to their semantic types.

### G. [Annex G (normative) IEC 60559-compatible complex arithmetic]

### G.1 [Introduction]

    1   This annex supplements annex F to specify complex arithmetic for compatibility with
        IEC 60559 real floating-point arithmetic. An implementation that defines
        _ _STDC_IEC_559_COMPLEX_ _ shall conform to the specifications in this annex.[375]

    Footnote 375) Implementations that do not define _ _STDC_IEC_559_COMPLEX_ _ are not required to conform
             to these specifications.

### G.2 [Types]

    1   There is a new keyword _Imaginary, which is used to specify imaginary types. It is
        used as a type specifier within declaration specifiers in the same way as _Complex is
        (thus, _Imaginary float is a valid type name).

    2   There are three imaginary types, designated as float _Imaginary, double
        _Imaginary, and long double _Imaginary. The imaginary types (along with
        the real floating and complex types) are floating types.

    3   For imaginary types, the corresponding real type is given by deleting the keyword
        _Imaginary from the type name.

    4   Each imaginary type has the same representation and alignment requirements as the
        corresponding real type. The value of an object of imaginary type is the value of the real
        representation times the imaginary unit.

    5   The imaginary type domain comprises the imaginary types.

### G.3 [Conventions]

    1   A complex or imaginary value with at least one infinite part is regarded as an infinity
        (even if its other part is a NaN). A complex or imaginary value is a finite number if each
        of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is
        a zero if each of its parts is a zero.

### G.4 [Conversions]

### G.4.1 [Imaginary types]

    1   Conversions among imaginary types follow rules analogous to those for real floating
        types.

### G.4.2 [Real and imaginary]

    1   When a value of imaginary type is converted to a real type other than _Bool,[376] the
        result is a positive zero.

    Footnote 376) See 6.3.1.2.

    2   When a value of real type is converted to an imaginary type, the result is a positive
        imaginary zero.

### G.4.3 [Imaginary and complex]

    1   When a value of imaginary type is converted to a complex type, the real part of the
        complex result value is a positive zero and the imaginary part of the complex result value
        is determined by the conversion rules for the corresponding real types.

    2   When a value of complex type is converted to an imaginary type, the real part of the
        complex value is discarded and the value of the imaginary part is converted according to
        the conversion rules for the corresponding real types.

### G.5 [Binary operators]

    1   The following subclauses supplement 6.5 in order to specify the type of the result for an
        operation with an imaginary operand.

    2   For most operand types, the value of the result of a binary operator with an imaginary or
        complex operand is completely determined, with reference to real arithmetic, by the usual
        mathematical formula. For some operand types, the usual mathematical formula is
        problematic because of its treatment of infinities and because of undue overflow or
        underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is
        not completely determined.

### G.5.1 [Multiplicative operators]

    1 Semantics
       If one operand has real type and the other operand has imaginary type, then the result has
        imaginary type. If both operands have imaginary type, then the result has real type. (If
        either operand has complex type, then the result has complex type.)

    2   If the operands are not both complex, then the result and floating-point exception
        behavior of the * operator is defined by the usual mathematical formula:
               *                  u                   iv                 u + iv

               x                  xu                i(xv)            (xu) + i(xv)

               iy               i(yu)                −yv            (−yv) + i(yu)

               x + iy       (xu) + i(yu)        (−yv) + i(xv)

    3   If the second operand is not complex, then the result and floating-point exception
        behavior of the / operator is defined by the usual mathematical formula:
               /                   u                       iv

               x                  x/u                 i(−x/v)

               iy               i(y/u)                     y/v

               x + iy       (x/u) + i(y/u)        (y/v) + i(−x/v)

    4   The * and / operators satisfy the following infinity properties for all real, imaginary, and
        complex operands:[377]
        — if one operand is an infinity and the other operand is a nonzero finite number or an
          infinity, then the result of the * operator is an infinity;
        — if the first operand is an infinity and the second operand is a finite number, then the
          result of the / operator is an infinity;
        — if the first operand is a finite number and the second operand is an infinity, then the
          result of the / operator is a zero;
        — if the first operand is a nonzero finite number or an infinity and the second operand is
          a zero, then the result of the / operator is an infinity.

    Footnote 377) These properties are already implied for those cases covered in the tables, but are required for all cases
             (at least where the state for CX_LIMITED_RANGE is ‘‘off’’).

    5   If both operands of the * operator are complex or if the second operand of the / operator
        is complex, the operator raises floating-point exceptions if appropriate for the calculation
        of the parts of the result, and may raise spurious floating-point exceptions.

    6   EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note
        that the imaginary unit I has imaginary type (see G.6).
               #include <math.h>
               #include <complex.h>
               /* Multiply z * w ... */
               double complex _Cmultd(double complex z, double complex w)
               {
                      #pragma STDC FP_CONTRACT OFF
                      double a, b, c, d, ac, bd, ad, bc, x, y;
                      a = creal(z); b = cimag(z);
                      c = creal(w); d = cimag(w);
                      ac = a * c;       bd = b * d;
                      ad = a * d;       bc = b * c;
                      x = ac - bd; y = ad + bc;
                      if (isnan(x) && isnan(y)) {
                              /* Recover infinities that computed as NaN+iNaN ... */
                              int recalc = 0;
                              if (isinf(a) || isinf(b)) { // z is infinite
                                      /* "Box" the infinity and change NaNs in the other factor to 0 */
                                      a = copysign(isinf(a) ? 1.0 : 0.0, a);
                                      b = copysign(isinf(b) ? 1.0 : 0.0, b);
                                      if (isnan(c)) c = copysign(0.0, c);
                                      if (isnan(d)) d = copysign(0.0, d);
                                      recalc = 1;
                              }
                              if (isinf(c) || isinf(d)) { // w is infinite
                                      /* "Box" the infinity and change NaNs in the other factor to 0 */
                                      c = copysign(isinf(c) ? 1.0 : 0.0, c);
                                      d = copysign(isinf(d) ? 1.0 : 0.0, d);
                                      if (isnan(a)) a = copysign(0.0, a);
                                      if (isnan(b)) b = copysign(0.0, b);
                                      recalc = 1;
                              }
                              if (!recalc && (isinf(ac) || isinf(bd) ||
                                                      isinf(ad) || isinf(bc))) {
                                      /* Recover infinities from overflow by changing NaNs to 0 ... */
                                      if (isnan(a)) a = copysign(0.0, a);
                                      if (isnan(b)) b = copysign(0.0, b);
                                      if (isnan(c)) c = copysign(0.0, c);
                                      if (isnan(d)) d = copysign(0.0, d);
                                      recalc = 1;
                              }
                              if (recalc) {
                                           x = INFINITY * ( a * c - b * d );
                                           y = INFINITY * ( a * d + b * c );
                               }
                         }
                         return x + I * y;
                }

    7   This implementation achieves the required treatment of infinities at the cost of only one isnan test in
        ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur.

    8   EXAMPLE 2      Division of two double _Complex operands could be implemented as follows.
                #include <math.h>
                #include <complex.h>
                /* Divide z / w ... */
                double complex _Cdivd(double complex z, double complex w)
                {
                       #pragma STDC FP_CONTRACT OFF
                       double a, b, c, d, logbw, denom, x, y;
                       int ilogbw = 0;
                       a = creal(z); b = cimag(z);
                       c = creal(w); d = cimag(w);
                       logbw = logb(fmax(fabs(c), fabs(d)));
                       if (isfinite(logbw)) {
                              ilogbw = (int)logbw;
                              c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw);
                       }
                       denom = c * c + d * d;
                       x = scalbn((a * c + b * d) / denom, -ilogbw);
                       y = scalbn((b * c - a * d) / denom, -ilogbw);
                         /* Recover infinities and zeros that computed as NaN+iNaN;                    */
                         /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */
                         if (isnan(x) && isnan(y)) {
                               if ((denom == 0.0) &&
                                     (!isnan(a) || !isnan(b))) {
                                     x = copysign(INFINITY, c) * a;
                                     y = copysign(INFINITY, c) * b;
                               }
                               else if ((isinf(a) || isinf(b)) &&
                                     isfinite(c) && isfinite(d)) {
                                     a = copysign(isinf(a) ? 1.0 : 0.0, a);
                                     b = copysign(isinf(b) ? 1.0 : 0.0, b);
                                     x = INFINITY * ( a * c + b * d );
                                     y = INFINITY * ( b * c - a * d );
                               }
                               else if ((logbw == INFINITY) &&
                                     isfinite(a) && isfinite(b)) {
                                     c = copysign(isinf(c) ? 1.0 : 0.0, c);
                                     d = copysign(isinf(d) ? 1.0 : 0.0, d);
                                     x = 0.0 * ( a * c + b * d );
                                     y = 0.0 * ( b * c - a * d );
                               }
                         }
                         return x + I * y;
                }

    9   Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than
        for multiplication. In the spirit of the multiplication example above, this code does not defend against
        overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of
        with division, provides better roundoff characteristics.

### G.5.2 [Additive operators]

    1 Semantics
       If both operands have imaginary type, then the result has imaginary type. (If one operand
        has real type and the other operand has imaginary type, or if either operand has complex
        type, then the result has complex type.)

    2   In all cases the result and floating-point exception behavior of a + or - operator is defined
        by the usual mathematical formula:
               + or −              u                       iv                    u + iv

               x                 x±u                     x ± iv              (x ± u) ± iv

               iy               ±u + iy                 i(y ± v)             ±u + i(y ± v)

               x + iy         (x ± u) + iy            x + i(y ± v)        (x ± u) + i(y ± v)

### G.6 [Complex arithmetic <complex.h>]

    1   The macros
                imaginary
        and
                _Imaginary_I
        are defined, respectively, as _Imaginary and a constant expression of type const
        float _Imaginary with the value of the imaginary unit. The macro
                I
        is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding
        the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro
        imaginary.

    2   This subclause contains specifications for the <complex.h> functions that are
        particularly suited to IEC 60559 implementations. For families of functions, the
        specifications apply to all of the functions even though only the principal function is
        shown. Unless otherwise specified, where the symbol ‘‘±’’ occurs in both an argument
        and the result, the result has the same sign as the argument.

    3   The functions are continuous onto both sides of their branch cuts, taking into account the
        sign of zero. For example, csqrt(−2 ± i0) = ±i√    ⎯ 2.

    4   Since complex and imaginary values are composed of real values, each function may be
        regarded as computing real values from real values. Except as noted, the functions treat
        real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a
        manner consistent with the specifications for real functions in F.10.[378]

    Footnote 378) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its
             other part is a NaN.

    5   The functions cimag, conj, cproj, and creal are fully specified for all
        implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating-
        point exceptions.

    6   Each of the functions cabs and carg is specified by a formula in terms of a real
        function (whose special cases are covered in annex F):
                 cabs(x + iy) = hypot(x, y)
                 carg(x + iy) = atan2(y, x)

    7   Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by
        a formula in terms of other complex functions (whose special cases are specified below):
                 casin(z) = −i casinh(iz)
                 catan(z) = −i catanh(iz)
                 ccos(z) = ccosh(iz)
                 csin(z) = −i csinh(iz)
                 ctan(z) = −i ctanh(iz)

    8   For the other functions, the following subclauses specify behavior for special cases,
        including treatment of the ‘‘invalid’’ and ‘‘divide-by-zero’’ floating-point exceptions. For
        families of functions, the specifications apply to all of the functions even though only the
        principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the
        specifications for the upper half-plane imply the specifications for the lower half-plane; if
        the function f is also either even, f (−z) = f (z), or odd, f (−z) = − f (z), then the
        specifications for the first quadrant imply the specifications for the other three quadrants.

    9   In the following subclauses, cis(y) is defined as cos(y) + i sin(y).

### G.6.1 [Trigonometric functions]

### G.6.1.1 [The cacos functions]

    1   — cacos(conj(z)) = conj(cacos(z)).
        — cacos(±0 + i0) returns π /2 − i0.
        — cacos(±0 + iNaN) returns π /2 + iNaN.
        — cacos(x + i ∞) returns π /2 − i ∞, for finite x.
        — cacos(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for nonzero finite x.
        — cacos(−∞ + iy) returns π − i ∞, for positive-signed finite y.
        — cacos(+∞ + iy) returns +0 − i ∞, for positive-signed finite y.
        — cacos(−∞ + i ∞) returns 3π /4 − i ∞.
        — cacos(+∞ + i ∞) returns π /4 − i ∞.
        — cacos(±∞ + iNaN) returns NaN ± i ∞ (where the sign of the imaginary part of the
          result is unspecified).
        — cacos(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite y.
        — cacos(NaN + i ∞) returns NaN − i ∞.
        — cacos(NaN + iNaN) returns NaN + iNaN.

### G.6.2 [Hyperbolic functions]

### G.6.2.1 [The cacosh functions]

    1   — cacosh(conj(z)) = conj(cacosh(z)).
        — cacosh(±0 + i0) returns +0 + iπ /2.
        — cacosh(x + i ∞) returns +∞ + iπ /2, for finite x.
        — cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’
          floating-point exception, for finite x.
        — cacosh(−∞ + iy) returns +∞ + iπ , for positive-signed finite y.
        — cacosh(+∞ + iy) returns +∞ + i0, for positive-signed finite y.
        — cacosh(−∞ + i ∞) returns +∞ + i3π /4.
        — cacosh(+∞ + i ∞) returns +∞ + iπ /4.
        — cacosh(±∞ + iNaN) returns +∞ + iNaN.
        — cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’
          floating-point exception, for finite y.
        — cacosh(NaN + i ∞) returns +∞ + iNaN.
        — cacosh(NaN + iNaN) returns NaN + iNaN.

### G.6.2.2 [The casinh functions]

    1   — casinh(conj(z)) = conj(casinh(z)) and casinh is odd.
        — casinh(+0 + i0) returns 0 + i0.
        — casinh(x + i ∞) returns +∞ + iπ /2 for positive-signed finite x.
        — casinh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’
          floating-point exception, for finite x.
        — casinh(+∞ + iy) returns +∞ + i0 for positive-signed finite y.
        — casinh(+∞ + i ∞) returns +∞ + iπ /4.
        — casinh(+∞ + iNaN) returns +∞ + iNaN.
        — casinh(NaN + i0) returns NaN + i0.
        — casinh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’
          floating-point exception, for finite nonzero y.
        — casinh(NaN + i ∞) returns ±∞ + iNaN (where the sign of the real part of the result
          is unspecified).
        — casinh(NaN + iNaN) returns NaN + iNaN.

### G.6.2.3 [The catanh functions]

    1   — catanh(conj(z)) = conj(catanh(z)) and catanh is odd.
        — catanh(+0 + i0) returns +0 + i0.
        — catanh(+0 + iNaN) returns +0 + iNaN.
        — catanh(+1 + i0) returns +∞ + i0 and raises the ‘‘divide-by-zero’’ floating-point
          exception.
        — catanh(x + i ∞) returns +0 + iπ /2, for finite positive-signed x.
        — catanh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’
          floating-point exception, for nonzero finite x.
        — catanh(+∞ + iy) returns +0 + iπ /2, for finite positive-signed y.
        — catanh(+∞ + i ∞) returns +0 + iπ /2.
        — catanh(+∞ + iNaN) returns +0 + iNaN.
        — catanh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’
          floating-point exception, for finite y.
        — catanh(NaN + i ∞) returns ±0 + iπ /2 (where the sign of the real part of the result is
          unspecified).
        — catanh(NaN + iNaN) returns NaN + iNaN.

### G.6.2.4 [The ccosh functions]

    1   — ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even.
        — ccosh(+0 + i0) returns 1 + i0.
        — ccosh(+0 + i ∞) returns NaN ± i0 (where the sign of the imaginary part of the
          result is unspecified) and raises the ‘‘invalid’’ floating-point exception.
        — ccosh(+0 + iNaN) returns NaN ± i0 (where the sign of the imaginary part of the
          result is unspecified).
        — ccosh(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
          exception, for finite nonzero x.
        — ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite nonzero x.
        — ccosh(+∞ + i0) returns +∞ + i0.
        — ccosh(+∞ + iy) returns +∞ cis(y), for finite nonzero y.
        — ccosh(+∞ + i ∞) returns ±∞ + iNaN (where the sign of the real part of the result is
          unspecified) and raises the ‘‘invalid’’ floating-point exception.
        — ccosh(+∞ + iNaN) returns +∞ + iNaN.
        — ccosh(NaN + i0) returns NaN ± i0 (where the sign of the imaginary part of the
          result is unspecified).
        — ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for all nonzero numbers y.
        — ccosh(NaN + iNaN) returns NaN + iNaN.

### G.6.2.5 [The csinh functions]

    1   — csinh(conj(z)) = conj(csinh(z)) and csinh is odd.
        — csinh(+0 + i0) returns +0 + i0.
        — csinh(+0 + i ∞) returns ±0 + iNaN (where the sign of the real part of the result is
          unspecified) and raises the ‘‘invalid’’ floating-point exception.
        — csinh(+0 + iNaN) returns ±0 + iNaN (where the sign of the real part of the result is
          unspecified).
        — csinh(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
          exception, for positive finite x.
        — csinh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite nonzero x.
        — csinh(+∞ + i0) returns +∞ + i0.
        — csinh(+∞ + iy) returns +∞ cis(y), for positive finite y.
        — csinh(+∞ + i ∞) returns ±∞ + iNaN (where the sign of the real part of the result is
          unspecified) and raises the ‘‘invalid’’ floating-point exception.
        — csinh(+∞ + iNaN) returns ±∞ + iNaN (where the sign of the real part of the result
          is unspecified).
        — csinh(NaN + i0) returns NaN + i0.
        — csinh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for all nonzero numbers y.
        — csinh(NaN + iNaN) returns NaN + iNaN.

### G.6.2.6 [The ctanh functions]

    1   — ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd.
        — ctanh(+0 + i0) returns +0 + i0.
        — ctanh(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
          exception, for finite x.
        — ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite x.
        — ctanh(+∞ + iy) returns 1 + i0 sin(2y), for positive-signed finite y.
        — ctanh(+∞ + i ∞) returns 1 ± i0 (where the sign of the imaginary part of the result
          is unspecified).
        — ctanh(+∞ + iNaN) returns 1 ± i0 (where the sign of the imaginary part of the
          result is unspecified).
        — ctanh(NaN + i0) returns NaN + i0.
        — ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for all nonzero numbers y.
        — ctanh(NaN + iNaN) returns NaN + iNaN.

### G.6.3 [Exponential and logarithmic functions]

### G.6.3.1 [The cexp functions]

    1   — cexp(conj(z)) = conj(cexp(z)).
        — cexp(±0 + i0) returns 1 + i0.
        — cexp(x + i ∞) returns NaN + iNaN and raises the ‘‘invalid’’ floating-point
          exception, for finite x.
        — cexp(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite x.
        — cexp(+∞ + i0) returns +∞ + i0.
        — cexp(−∞ + iy) returns +0 cis(y), for finite y.
        — cexp(+∞ + iy) returns +∞ cis(y), for finite nonzero y.
        — cexp(−∞ + i ∞) returns ±0 ± i0 (where the signs of the real and imaginary parts of
          the result are unspecified).
        — cexp(+∞ + i ∞) returns ±∞ + iNaN and raises the ‘‘invalid’’ floating-point
          exception (where the sign of the real part of the result is unspecified).
        — cexp(−∞ + iNaN) returns ±0 ± i0 (where the signs of the real and imaginary parts
          of the result are unspecified).
        — cexp(+∞ + iNaN) returns ±∞ + iNaN (where the sign of the real part of the result
          is unspecified).
        — cexp(NaN + i0) returns NaN + i0.
        — cexp(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for all nonzero numbers y.
        — cexp(NaN + iNaN) returns NaN + iNaN.

### G.6.3.2 [The clog functions]

    1   — clog(conj(z)) = conj(clog(z)).
        — clog(−0 + i0) returns −∞ + iπ and raises the ‘‘divide-by-zero’’ floating-point
          exception.
        — clog(+0 + i0) returns −∞ + i0 and raises the ‘‘divide-by-zero’’ floating-point
          exception.
        — clog(x + i ∞) returns +∞ + iπ /2, for finite x.
        — clog(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite x.
        — clog(−∞ + iy) returns +∞ + iπ , for finite positive-signed y.
        — clog(+∞ + iy) returns +∞ + i0, for finite positive-signed y.
        — clog(−∞ + i ∞) returns +∞ + i3π /4.
        — clog(+∞ + i ∞) returns +∞ + iπ /4.
        — clog(±∞ + iNaN) returns +∞ + iNaN.
        — clog(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite y.
        — clog(NaN + i ∞) returns +∞ + iNaN.
        — clog(NaN + iNaN) returns NaN + iNaN.

### G.6.4 [Power and absolute-value functions]

### G.6.4.1 [The cpow functions]

    1   The cpow functions raise floating-point exceptions if appropriate for the calculation of
        the parts of the result, and may also raise spurious floating-point exceptions.[379]

    Footnote 379) This allows cpow( z , c ) to be implemented as cexp(c      clog( z )) without precluding
             implementations that treat special cases more carefully.

### G.6.4.2 [The csqrt functions]

    1   — csqrt(conj(z)) = conj(csqrt(z)).
        — csqrt(±0 + i0) returns +0 + i0.
        — csqrt(x + i ∞) returns +∞ + i ∞, for all x (including NaN).
        — csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite x.
        — csqrt(−∞ + iy) returns +0 + i ∞, for finite positive-signed y.
        — csqrt(+∞ + iy) returns +∞ + i0, for finite positive-signed y.
        — csqrt(−∞ + iNaN) returns NaN ± i ∞ (where the sign of the imaginary part of the
          result is unspecified).
        — csqrt(+∞ + iNaN) returns +∞ + iNaN.
        — csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ‘‘invalid’’ floating-
          point exception, for finite y.
        — csqrt(NaN + iNaN) returns NaN + iNaN.

### G.7 [Type-generic math <tgmath.h>]

    1   Type-generic macros that accept complex arguments also accept imaginary arguments. If
        an argument is imaginary, the macro expands to an expression whose type is real,
        imaginary, or complex, as appropriate for the particular function: if the argument is
        imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the
        types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and
        the types of the others are complex.

    2   Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh,
        sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real
        functions:
               cos(iy)   = cosh(y)
               sin(iy)   = i sinh(y)
               tan(iy)   = i tanh(y)
               cosh(iy) = cos(y)
               sinh(iy) = i sin(y)
               tanh(iy) = i tan(y)
               asin(iy) = i asinh(y)
               atan(iy) = i atanh(y)
               asinh(iy) = i asin(y)
               atanh(iy) = i atan(y)

### H. [Annex H (informative) Language independent arithmetic]

### H.1 [Introduction]

    1   This annex documents the extent to which the C language supports the ISO/IEC 10967−1
        standard for language-independent arithmetic (LIA−1). LIA−1 is more general than
        IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics.

### H.2 [Types]

    1   The relevant C arithmetic types meet the requirements of LIA−1 types if an
        implementation adds notification of exceptional arithmetic operations and meets the 1
        unit in the last place (ULP) accuracy requirement (LIA−1 subclause 5.2.8).

### H.2.1 [Boolean type]

    1   The LIA−1 data type Boolean is implemented by the C data type bool with values of
        true and false, all from <stdbool.h>.

### H.2.2 [Integer types]

    1   The signed C integer types int, long int, long long int, and the corresponding
        unsigned types are compatible with LIA−1. If an implementation adds support for the
        LIA−1 exceptional values ‘‘integer_overflow’’ and ‘‘undefined’’, then those types are
        LIA−1 conformant types. C’s unsigned integer types are ‘‘modulo’’ in the LIA−1 sense
        in that overflows or out-of-bounds results silently wrap. An implementation that defines
        signed integer types as also being modulo need not detect integer overflow, in which case,
        only integer divide-by-zero need be detected.

    2   The parameters for the integer data types can be accessed by the following:
        maxint        INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX,
                      ULLONG_MAX
        minint        INT_MIN, LONG_MIN, LLONG_MIN

    3   The parameter ‘‘bounded’’ is always true, and is not provided. The parameter ‘‘minint’’
        is always 0 for the unsigned types, and is not provided for those types.

### H.2.2.1 [Integer operations]

    1   The integer operations on integer types are the following:
        addI           x + y
        subI           x - y
        mulI           x * y
        divI, divtI    x / y
        remI, remtI    x % y
        negI           -x
        absI           abs(x), labs(x), llabs(x)
        eqI            x == y
        neqI           x != y
        lssI           x < y
        leqI           x <= y
        gtrI           x > y
        geqI           x >= y
        where x and y are expressions of the same integer type.

### H.2.3 [Floating-point types]

    1   The C floating-point types float, double, and long double are compatible with
        LIA−1. If an implementation adds support for the LIA−1 exceptional values
        ‘‘underflow’’, ‘‘floating_overflow’’, and ‘‘"undefined’’, then those types are conformant
        with LIA−1. An implementation that uses IEC 60559 floating-point formats and
        operations (see annex F) along with IEC 60559 status flags and traps has LIA−1
        conformant types.

### H.2.3.1 [Floating-point parameters]

    1   The parameters for a floating point data type can be accessed by the following:
        r              FLT_RADIX
        p              FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG
        emax           FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP
        emin           FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP

    2   The derived constants for the floating point types are accessed by the following:
        fmax           FLT_MAX, DBL_MAX, LDBL_MAX
        fminN          FLT_MIN, DBL_MIN, LDBL_MIN
        epsilon        FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON
        rnd_style      FLT_ROUNDS

### H.2.3.2 [Floating-point operations]

    1   The floating-point operations on floating-point types are the following:
        addF           x + y
        subF           x - y
        mulF           x * y
        divF           x / y
        negF           -x
        absF           fabsf(x), fabs(x), fabsl(x)
        exponentF      1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)
        scaleF         scalbnf(x, n), scalbn(x, n), scalbnl(x, n),
                       scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
        intpartF       modff(x, &y), modf(x, &y), modfl(x, &y)
        fractpartF     modff(x, &y), modf(x, &y), modfl(x, &y)
        eqF            x == y
        neqF           x != y
        lssF           x < y
        leqF           x <= y
        gtrF           x > y
        geqF           x >= y
        where x and y are expressions of the same floating point type, n is of type int, and li
        is of type long int.

### H.2.3.3 [Rounding styles]

    1   The C Standard requires all floating types to use the same radix and rounding style, so
        that only one identifier for each is provided to map to LIA−1.

    2   The FLT_ROUNDS parameter can be used to indicate the LIA−1 rounding styles:
        truncate       FLT_ROUNDS == 0
        nearest       FLT_ROUNDS == 1
        other         FLT_ROUNDS != 0 && FLT_ROUNDS != 1
        provided that an implementation extends FLT_ROUNDS to cover the rounding style used
        in all relevant LIA−1 operations, not just addition as in C.

### H.2.4 [Type conversions]

    1   The LIA−1 type conversions are the following type casts:
        cvtI’ → I     (int)i, (long int)i, (long long int)i,
                      (unsigned int)i, (unsigned long int)i,
                      (unsigned long long int)i
        cvtF → I      (int)x, (long int)x, (long long int)x,
                      (unsigned int)x, (unsigned long int)x,
                      (unsigned long long int)x
        cvtI → F      (float)i, (double)i, (long double)i
        cvtF’ → F     (float)x, (double)x, (long double)x

    2   In the above conversions from floating to integer, the use of (cast)x can be replaced with
        (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),
        (cast)ceil(x), or (cast)floor(x). In addition, C’s floating-point to integer
        conversion functions, lrint(), llrint(), lround(), and llround(), can be
        used. They all meet LIA−1’s requirements on floating to integer rounding for in-range
        values. For out-of-range values, the conversions shall silently wrap for the modulo types.

    3   The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g.,
        fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x),
        65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0
        to 65535.0 which can then be cast to unsigned short int. But, the
        remainder() function is not useful for doing silent wrapping to signed integer types,
        e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the
        range −32767.0 to +32768.0 which is not, in general, in the range of signed short
        int.

    4   C’s conversions (casts) from floating-point to floating-point can meet LIA−1
        requirements if an implementation uses round-to-nearest (IEC 60559 default).

    5   C’s conversions (casts) from integer to floating-point can meet LIA−1 requirements if an
        implementation uses round-to-nearest.

### H.3 [Notification]

    1   Notification is the process by which a user or program is informed that an exceptional
        arithmetic operation has occurred. C’s operations are compatible with LIA−1 in that C
        allows an implementation to cause a notification to occur when any arithmetic operation
        returns an exceptional value as defined in LIA−1 clause 5.

### H.3.1 [Notification alternatives]

    1   LIA−1 requires at least the following two alternatives for handling of notifications:
        setting indicators or trap-and-terminate. LIA−1 allows a third alternative: trap-and-
        resume.

    2   An implementation need only support a given notification alternative for the entire
        program. An implementation may support the ability to switch between notification
        alternatives during execution, but is not required to do so. An implementation can
        provide separate selection for each kind of notification, but this is not required.

    3   C allows an implementation to provide notification. C’s SIGFPE (for traps) and
        FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators)
        can provide LIA−1 notification.

    4   C’s signal handlers are compatible with LIA−1. Default handling of SIGFPE can
        provide trap-and-terminate behavior, except for those LIA−1 operations implemented by
        math library function calls. User-provided signal handlers for SIGFPE allow for trap-
        and-resume behavior with the same constraint.

### H.3.1.1 [Indicators]

    1   C’s <fenv.h> status flags are compatible with the LIA−1 indicators.

    2   The following mapping is for floating-point types:
        undefined                FE_INVALID, FE_DIVBYZERO
        floating_overflow        FE_OVERFLOW
        underflow                FE_UNDERFLOW

    3   The floating-point indicator interrogation and manipulation operations are:
        set_indicators           feraiseexcept(i)
        clear_indicators         feclearexcept(i)
        test_indicators          fetestexcept(i)
        current_indicators       fetestexcept(FE_ALL_EXCEPT)
        where i is an expression of type int representing a subset of the LIA−1 indicators.

    4   C allows an implementation to provide the following LIA−1 required behavior: at
        and ‘‘hard to ignore’’ message (see LIA−1 subclause 6.1.2)

    5   LIA−1 does not make the distinction between floating-point and integer for ‘‘undefined’’.
        This documentation makes that distinction because <fenv.h> covers only the floating-
        point indicators.

### H.3.1.2 [Traps]

    1   C is compatible with LIA−1’s trap requirements for arithmetic operations, but not for
        math library functions (which are not permitted to invoke a user’s signal handler for
        SIGFPE). An implementation can provide an alternative of notification through
        termination with a ‘‘hard-to-ignore’’ message (see LIA−1 subclause 6.1.3).

    2   LIA−1 does not require that traps be precise.

    3   C does require that SIGFPE be the signal corresponding to LIA−1 arithmetic exceptions,
        if there is any signal raised for them.

    4   C supports signal handlers for SIGFPE and allows trapping of LIA−1 arithmetic
        exceptions. When LIA−1 arithmetic exceptions do trap, C’s signal-handler mechanism
        allows trap-and-terminate (either default implementation behavior or user replacement for
        it) or trap-and-resume, at the programmer’s option.

### I. [Annex I (informative) Common warnings]

    1   An implementation may generate warnings in many situations, none of which are
        specified as part of this International Standard. The following are a few of the more
        common situations.

    2   — A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3).
        — A block with initialization of an object that has automatic storage duration is jumped
          into (6.2.4).
        — An implicit narrowing conversion is encountered, such as the assignment of a long
          int or a double to an int, or a pointer to void to a pointer to any type other than
          a character type (6.3).
        — A hexadecimal floating constant cannot be represented exactly in its evaluation format
          (6.4.4.2).
        — An integer character constant includes more than one character or a wide character
          constant includes more than one multibyte character (6.4.4.4).
        — The characters /* are found in a comment (6.4.7).
        — An ‘‘unordered’’ binary operator (not comma, &&, or ||) contains a side effect to an
          lvalue in one operand, and a side effect to, or an access to the value of, the identical
          lvalue in the other operand (6.5).
        — A function is called but no prototype has been supplied (6.5.2.2).
        — The arguments in a function call do not agree in number and type with those of the
          parameters in a function definition that is not a prototype (6.5.2.2).
        — An object is defined but not used (6.7).
        — A value is given to an object of an enumerated type other than by assignment of an
          enumeration constant that is a member of that type, or an enumeration object that has
          the same type, or the value of a function that returns the same enumerated type
          (6.7.2.2).
        — An aggregate has a partly bracketed initialization (6.7.8).
        — A statement cannot be reached (6.8).
        — A statement with no apparent effect is encountered (6.8).
        — A constant expression is used as the controlling expression of a selection statement
          (6.8.4).
    — An incorrectly formed preprocessing group is encountered while skipping a
      preprocessing group (6.10.1).
    — An unrecognized #pragma directive is encountered (6.10.6).

### J. [Annex J (informative) Portability issues]

    1   This annex collects some information about portability that appears in this International
        Standard.

### J.1 [Unspecified behavior]

    1   The following are unspecified:
        — The manner and timing of static initialization (5.1.2).
        — The termination status returned to the hosted environment if the return type of main
          is not compatible with int (5.1.2.2.3).
        — The values of objects that are neither lock-free atomic objects nor of type volatile
          sig_atomic_t and the state of the floating-point environment, when the
          processing of the abstract machine is interrupted by receipt of a signal (5.1.2.3).
        — The behavior of the display device if a printing character is written when the active
          position is at the final position of a line (5.2.2).
        — The behavior of the display device if a backspace character is written when the active
          position is at the initial position of a line (5.2.2).
        — The behavior of the display device if a horizontal tab character is written when the
          active position is at or past the last defined horizontal tabulation position (5.2.2).
        — The behavior of the display device if a vertical tab character is written when the active
          position is at or past the last defined vertical tabulation position (5.2.2).
        — How an extended source character that does not correspond to a universal character
          name counts toward the significant initial characters in an external identifier (5.2.4.1).
        — Many aspects of the representations of types (6.2.6).
        — The value of padding bytes when storing values in structures or unions (6.2.6.1).
        — The values of bytes that correspond to union members other than the one last stored
          into (6.2.6.1).
        — The representation used when storing a value in an object that has more than one
          object representation for that value (6.2.6.1).
        — The values of any padding bits in integer representations (6.2.6.2).
        — Whether certain operators can generate negative zeros and whether a negative zero
          becomes a normal zero when stored in an object (6.2.6.2).
    — Whether two string literals result in distinct arrays (6.4.5).
    — The order in which subexpressions are evaluated and the order in which side effects
      take place, except as specified for the function-call (), &&, ||, ? :, and comma
      operators (6.5).
    — The order in which the function designator, arguments, and subexpressions within the
      arguments are evaluated in a function call (6.5.2.2).
    — The order of side effects among compound literal initialization list expressions
      (6.5.2.5).
    — The order in which the operands of an assignment operator are evaluated (6.5.16).
    — The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1).
    — Whether a call to an inline function uses the inline definition or the external definition
      of the function (6.7.4).
    — Whether or not a size expression is evaluated when it is part of the operand of a
      sizeof operator and changing the value of the size expression would not affect the
      result of the operator (6.7.6.2).
    — The order in which any side effects occur among the initialization list expressions in
      an initializer (6.7.9).
    — The layout of storage for function parameters (6.9.1).
    — When a fully expanded macro replacement list contains a function-like macro name
      as its last preprocessing token and the next preprocessing token from the source file is
      a (, and the fully expanded replacement of that macro ends with the name of the first
      macro and the next preprocessing token from the source file is again a (, whether that
      is considered a nested replacement (6.10.3).
    — The order in which # and ## operations are evaluated during macro substitution
      (6.10.3.2, 6.10.3.3).
    — The state of the floating-point status flags when execution passes from a part of the
      program translated with FENV_ACCESS ‘‘off’’ to a part translated with
      FENV_ACCESS ‘‘on’’ (7.6.1).
    — The order in which feraiseexcept raises floating-point exceptions, except as
      stated in F.8.6 (7.6.2.3).
    — Whether math_errhandling is a macro or an identifier with external linkage
      (7.12).
    — The results of the frexp functions when the specified value is not a floating-point
      number (7.12.6.4).
    — The numeric result of the ilogb functions when the correct value is outside the
      range of the return type (7.12.6.5, F.10.3.5).
    — The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5).
    — The value stored by the remquo functions in the object pointed to by quo when y is
      zero (7.12.10.3).
    — Whether a comparison macro argument that is represented in a format wider than its
      semantic type is converted to the semantic type (7.12.14).
    — Whether setjmp is a macro or an identifier with external linkage (7.13).
    — Whether va_copy and va_end are macros or identifiers with external linkage
      (7.16.1).
    — The hexadecimal digit before the decimal point when a non-normalized floating-point
      number is printed with an a or A conversion specifier (7.21.6.1, 7.29.2.1).
    — The value of the file position indicator after a successful call to the ungetc function
      for a text stream, or the ungetwc function for any stream, until all pushed-back
      characters are read or discarded (7.21.7.10, 7.29.3.10).
    — The details of the value stored by the fgetpos function (7.21.9.1).
    — The details of the value returned by the ftell function for a text stream (7.21.9.4).
    — Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold
      functions convert a minus-signed sequence to a negative number directly or by
      negating the value resulting from converting the corresponding unsigned sequence
      (7.22.1.3, 7.29.4.1.1).
    — The order and contiguity of storage allocated by successive calls to the calloc,
      malloc, and realloc functions (7.22.3).
    — The amount of storage allocated by a successful call to the calloc, malloc, or
      realloc function when 0 bytes was requested (7.22.3).
    — Whether a call to the atexit function that does not happen before the exit
      function is called will succeed (7.22.4.2).
    — Whether a call to the at_quick_exit function that does not happen before the
      quick_exit function is called will succeed (7.22.4.3).
    — Which of two elements that compare as equal is matched by the bsearch function
      (7.22.5.1).
    — The order of two elements that compare as equal in an array sorted by the qsort
      function (7.22.5.2).
        — The encoding of the calendar time returned by the time function (7.27.2.4).
        — The characters stored by the strftime or wcsftime function if any of the time
          values being converted is outside the normal range (7.27.3.5, 7.29.5.1).
        — Whether an encoding error occurs if a wchar_t value that does not correspond to a
          member of the extended character set appears in the format string for a function in
          7.29.2 or 7.29.5 and the specified semantics do not require that value to be processed
          by wcrtomb (7.29.1).
        — The conversion state after an encoding error occurs (7.29.6.3.2, 7.29.6.3.3, 7.29.6.4.1,
          7.29.6.4.2,
        — The resulting value when the ‘‘invalid’’ floating-point exception is raised during
          IEC 60559 floating to integer conversion (F.4).
        — Whether conversion of non-integer IEC 60559 floating values to integer raises the
          ‘‘inexact’’ floating-point exception (F.4).
        — Whether or when library functions in <math.h> raise the ‘‘inexact’’ floating-point
          exception in an IEC 60559 conformant implementation (F.10).
        — Whether or when library functions in <math.h> raise an undeserved ‘‘underflow’’
          floating-point exception in an IEC 60559 conformant implementation (F.10).
        — The exponent value stored by frexp for a NaN or infinity (F.10.3.4).
        — The numeric result returned by the lrint, llrint, lround, and llround
          functions if the rounded value is outside the range of the return type (F.10.6.5,
          F.10.6.7).
        — The sign of one part of the complex result of several math functions for certain
          special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3,
          G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2).

### J.2 [Undefined behavior]

    1   The behavior is undefined in the following circumstances:
        — A ‘‘shall’’ or ‘‘shall not’’ requirement that appears outside of a constraint is violated
          (clause 4).
        — A nonempty source file does not end in a new-line character which is not immediately
          preceded by a backslash character or ends in a partial preprocessing token or
          comment (5.1.1.2).
        — Token concatenation produces a character sequence matching the syntax of a
          universal character name (5.1.1.2).
        — A program in a hosted environment does not define a function named main using one
          of the specified forms (5.1.2.2.1).
    — The execution of a program contains a data race (5.1.2.4).
    — A character not in the basic source character set is encountered in a source file, except
      in an identifier, a character constant, a string literal, a header name, a comment, or a
      preprocessing token that is never converted to a token (5.2.1).
    — An identifier, comment, string literal, character constant, or header name contains an
      invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2).
    — The same identifier has both internal and external linkage in the same translation unit
      (6.2.2).
    — An object is referred to outside of its lifetime (6.2.4).
    — The value of a pointer to an object whose lifetime has ended is used (6.2.4).
    — The value of an object with automatic storage duration is used while it is
      indeterminate (6.2.4, 6.7.9, 6.8).
    — A trap representation is read by an lvalue expression that does not have character type
      (6.2.6.1).
    — A trap representation is produced by a side effect that modifies any part of the object
      using an lvalue expression that does not have character type (6.2.6.1).
    — The operands to certain operators are such that they could produce a negative zero
      result, but the implementation does not support negative zeros (6.2.6.2).
    — Two declarations of the same object or function specify types that are not compatible
      (6.2.7).
    — A program requires the formation of a composite type from a variable length array
      type whose size is specified by an expression that is not evaluated (6.2.7).
    — Conversion to or from an integer type produces a value outside the range that can be
      represented (6.3.1.4).
    — Demotion of one real floating type to another produces a value outside the range that
      can be represented (6.3.1.5).
    — An lvalue does not designate an object when evaluated (6.3.2.1).
    — A non-array lvalue with an incomplete type is used in a context that requires the value
      of the designated object (6.3.2.1).
    — An lvalue designating an object of automatic storage duration that could have been
      declared with the register storage class is used in a context that requires the value
      of the designated object, but the object is uninitialized. (6.3.2.1).
    — An lvalue having array type is converted to a pointer to the initial element of the
      array, and the array object has register storage class (6.3.2.1).
    — An attempt is made to use the value of a void expression, or an implicit or explicit
      conversion (except to void) is applied to a void expression (6.3.2.2).
    — Conversion of a pointer to an integer type produces a value outside the range that can
      be represented (6.3.2.3).
    — Conversion between two pointer types produces a result that is incorrectly aligned
      (6.3.2.3).
    — A pointer is used to call a function whose type is not compatible with the referenced
      type (6.3.2.3).
    — An unmatched ' or " character is encountered on a logical source line during
      tokenization (6.4).
    — A reserved keyword token is used in translation phase 7 or 8 for some purpose other
      than as a keyword (6.4.1).
    — A universal character name in an identifier does not designate a character whose
      encoding falls into one of the specified ranges (6.4.2.1).
    — The initial character of an identifier is a universal character name designating a digit
      (6.4.2.1).
    — Two identifiers differ only in nonsignificant characters (6.4.2.1).
    — The identifier _ _func_ _ is explicitly declared (6.4.2.2).
    — The program attempts to modify a string literal (6.4.5).
    — The characters ', \, ", //, or /* occur in the sequence between the < and >
      delimiters, or the characters ', \, //, or /* occur in the sequence between the "
      delimiters, in a header name preprocessing token (6.4.7).
    — A side effect on a scalar object is unsequenced relative to either a different side effect
      on the same scalar object or a value computation using the value of the same scalar
      object (6.5).
    — An exceptional condition occurs during the evaluation of an expression (6.5).
    — An object has its stored value accessed other than by an lvalue of an allowable type
      (6.5).
    — For a call to a function without a function prototype in scope, the number of
      arguments does not equal the number of parameters (6.5.2.2).
    — For call to a function without a function prototype in scope where the function is
      defined with a function prototype, either the prototype ends with an ellipsis or the
      types of the arguments after promotion are not compatible with the types of the
      parameters (6.5.2.2).
    — For a call to a function without a function prototype in scope where the function is not
      defined with a function prototype, the types of the arguments after promotion are not
      compatible with those of the parameters after promotion (with certain exceptions)
      (6.5.2.2).
    — A function is defined with a type that is not compatible with the type (of the
      expression) pointed to by the expression that denotes the called function (6.5.2.2).
    — A member of an atomic structure or union is accessed (6.5.2.3).
    — The operand of the unary * operator has an invalid value (6.5.3.2).
    — A pointer is converted to other than an integer or pointer type (6.5.4).
    — The value of the second operand of the / or % operator is zero (6.5.5).
    — Addition or subtraction of a pointer into, or just beyond, an array object and an
      integer type produces a result that does not point into, or just beyond, the same array
      object (6.5.6).
    — Addition or subtraction of a pointer into, or just beyond, an array object and an
      integer type produces a result that points just beyond the array object and is used as
      the operand of a unary * operator that is evaluated (6.5.6).
    — Pointers that do not point into, or just beyond, the same array object are subtracted
      (6.5.6).
    — An array subscript is out of range, even if an object is apparently accessible with the
      given subscript (as in the lvalue expression a[1][7] given the declaration int
      a[4][5]) (6.5.6).
    — The result of subtracting two pointers is not representable in an object of type
      ptrdiff_t (6.5.6).
    — An expression is shifted by a negative number or by an amount greater than or equal
      to the width of the promoted expression (6.5.7).
    — An expression having signed promoted type is left-shifted and either the value of the
      expression is negative or the result of shifting would be not be representable in the
      promoted type (6.5.7).
    — Pointers that do not point to the same aggregate or union (nor just beyond the same
      array object) are compared using relational operators (6.5.8).
    — An object is assigned to an inexactly overlapping object or to an exactly overlapping
      object with incompatible type (6.5.16.1).
    — An expression that is required to be an integer constant expression does not have an
      integer type; has operands that are not integer constants, enumeration constants,
      character constants, sizeof expressions whose results are integer constants,
       _Alignof expressions, or immediately-cast floating constants; or contains casts
       (outside operands to sizeof and _Alignof operators) other than conversions of
       arithmetic types to integer types (6.6).
    — A constant expression in an initializer is not, or does not evaluate to, one of the
      following: an arithmetic constant expression, a null pointer constant, an address
      constant, or an address constant for a complete object type plus or minus an integer
      constant expression (6.6).
    — An arithmetic constant expression does not have arithmetic type; has operands that
      are not integer constants, floating constants, enumeration constants, character
      constants, sizeof expressions whose results are integer constants, or _Alignof
      expressions; or contains casts (outside operands to sizeof or _Alignof operators)
      other than conversions of arithmetic types to arithmetic types (6.6).
    — The value of an object is accessed by an array-subscript [], member-access . or −>,
      address &, or indirection * operator or a pointer cast in creating an address constant
      (6.6).
    — An identifier for an object is declared with no linkage and the type of the object is
      incomplete after its declarator, or after its init-declarator if it has an initializer (6.7).
    — A function is declared at block scope with an explicit storage-class specifier other
      than extern (6.7.1).
    — A structure or union is defined without any named members (including those
      specified indirectly via anonymous structures and unions) (6.7.2.1).
    — An attempt is made to access, or generate a pointer to just past, a flexible array
      member of a structure when the referenced object provides no elements for that array
      (6.7.2.1).
    — When the complete type is needed, an incomplete structure or union type is not
      completed in the same scope by another declaration of the tag that defines the content
      (6.7.2.3).
    — An attempt is made to modify an object defined with a const-qualified type through
      use of an lvalue with non-const-qualified type (6.7.3).
    — An attempt is made to refer to an object defined with a volatile-qualified type through
      use of an lvalue with non-volatile-qualified type (6.7.3).
    — The specification of a function type includes any type qualifiers (6.7.3).
    — Two qualified types that are required to be compatible do not have the identically
      qualified version of a compatible type (6.7.3).
    — An object which has been modified is accessed through a restrict-qualified pointer to
      a const-qualified type, or through a restrict-qualified pointer and another pointer that
       are not both based on the same object (6.7.3.1).
    — A restrict-qualified pointer is assigned a value based on another restricted pointer
      whose associated block neither began execution before the block associated with this
      pointer, nor ended before the assignment (6.7.3.1).
    — A function with external linkage is declared with an inline function specifier, but is
      not also defined in the same translation unit (6.7.4).
    — A function declared with a _Noreturn function specifier returns to its caller (6.7.4).
    — The definition of an object has an alignment specifier and another declaration of that
      object has a different alignment specifier (6.7.5).
    — Declarations of an object in different translation units have different alignment
      specifiers (6.7.5).
    — Two pointer types that are required to be compatible are not identically qualified, or
      are not pointers to compatible types (6.7.6.1).
    — The size expression in an array declaration is not a constant expression and evaluates
      at program execution time to a nonpositive value (6.7.6.2).
    — In a context requiring two array types to be compatible, they do not have compatible
      element types, or their size specifiers evaluate to unequal values (6.7.6.2).
    — A declaration of an array parameter includes the keyword static within the [ and
      ] and the corresponding argument does not provide access to the first element of an
      array with at least the specified number of elements (6.7.6.3).
    — A storage-class specifier or type qualifier modifies the keyword void as a function
      parameter type list (6.7.6.3).
    — In a context requiring two function types to be compatible, they do not have
      compatible return types, or their parameters disagree in use of the ellipsis terminator
      or the number and type of parameters (after default argument promotion, when there
      is no parameter type list or when one type is specified by a function definition with an
      identifier list) (6.7.6.3).
    — The value of an unnamed member of a structure or union is used (6.7.9).
    — The initializer for a scalar is neither a single expression nor a single expression
      enclosed in braces (6.7.9).
    — The initializer for a structure or union object that has automatic storage duration is
      neither an initializer list nor a single expression that has compatible structure or union
      type (6.7.9).
    — The initializer for an aggregate or union, other than an array initialized by a string
      literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9).
    — An identifier with external linkage is used, but in the program there does not exist
      exactly one external definition for the identifier, or the identifier is not used and there
      exist multiple external definitions for the identifier (6.9).
    — A function definition includes an identifier list, but the types of the parameters are not
      declared in a following declaration list (6.9.1).
    — An adjusted parameter type in a function definition is not a complete object type
      (6.9.1).
    — A function that accepts a variable number of arguments is defined without a
      parameter type list that ends with the ellipsis notation (6.9.1).
    — The } that terminates a function is reached, and the value of the function call is used
      by the caller (6.9.1).
    — An identifier for an object with internal linkage and an incomplete type is declared
      with a tentative definition (6.9.2).
    — The token defined is generated during the expansion of a #if or #elif
      preprocessing directive, or the use of the defined unary operator does not match
      one of the two specified forms prior to macro replacement (6.10.1).
    — The #include preprocessing directive that results after expansion does not match
      one of the two header name forms (6.10.2).
    — The character sequence in an #include preprocessing directive does not start with a
      letter (6.10.2).
    — There are sequences of preprocessing tokens within the list of macro arguments that
      would otherwise act as preprocessing directives (6.10.3).
    — The result of the preprocessing operator # is not a valid character string literal
      (6.10.3.2).
    — The result of the preprocessing operator ## is not a valid preprocessing token
      (6.10.3.3).
    — The #line preprocessing directive that results after expansion does not match one of
      the two well-defined forms, or its digit sequence specifies zero or a number greater
      than 2147483647 (6.10.4).
    — A non-STDC #pragma preprocessing directive that is documented as causing
      translation failure or some other form of undefined behavior is encountered (6.10.6).
    — A #pragma STDC preprocessing directive does not match one of the well-defined
      forms (6.10.6).
    — The name of a predefined macro, or the identifier defined, is the subject of a
      #define or #undef preprocessing directive (6.10.8).
    — An attempt is made to copy an object to an overlapping object by use of a library
      function, other than as explicitly allowed (e.g., memmove) (clause 7).
    — A file with the same name as one of the standard headers, not provided as part of the
      implementation, is placed in any of the standard places that are searched for included
      source files (7.1.2).
    — A header is included within an external declaration or definition (7.1.2).
    — A function, object, type, or macro that is specified as being declared or defined by
      some standard header is used before any header that declares or defines it is included
      (7.1.2).
    — A standard header is included while a macro is defined with the same name as a
      keyword (7.1.2).
    — The program attempts to declare a library function itself, rather than via a standard
      header, but the declaration does not have external linkage (7.1.2).
    — The program declares or defines a reserved identifier, other than as allowed by 7.1.4
      (7.1.3).
    — The program removes the definition of a macro whose name begins with an
      underscore and either an uppercase letter or another underscore (7.1.3).
    — An argument to a library function has an invalid value or a type not expected by a
      function with variable number of arguments (7.1.4).
    — The pointer passed to a library function array parameter does not have a value such
      that all address computations and object accesses are valid (7.1.4).
    — The macro definition of assert is suppressed in order to access an actual function
      (7.2).
    — The argument to the assert macro does not have a scalar type (7.2).
    — The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in
      any context other than outside all external declarations or preceding all explicit
      declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2).
    — The value of an argument to a character handling function is neither equal to the value
      of EOF nor representable as an unsigned char (7.4).
    — A macro definition of errno is suppressed in order to access an actual object, or the
      program defines an identifier with the name errno (7.5).
    — Part of the program tests floating-point status flags, sets floating-point control modes,
      or runs under non-default mode settings, but was translated with the state for the
      FENV_ACCESS pragma ‘‘off’’ (7.6.1).
    — The exception-mask argument for one of the functions that provide access to the
      floating-point status flags has a nonzero value not obtained by bitwise OR of the
      floating-point exception macros (7.6.2).
    — The fesetexceptflag function is used to set floating-point status flags that were
      not specified in the call to the fegetexceptflag function that provided the value
      of the corresponding fexcept_t object (7.6.2.4).
    — The argument to fesetenv or feupdateenv is neither an object set by a call to
      fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4).
    — The value of the result of an integer arithmetic or conversion function cannot be
      represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.22.6.1, 7.22.6.2, 7.22.1).
    — The program modifies the string pointed to by the value returned by the setlocale
      function (7.11.1.1).
    — The program modifies the structure pointed to by the value returned by the
      localeconv function (7.11.2.1).
    — A macro definition of math_errhandling is suppressed or the program defines
      an identifier with the name math_errhandling (7.12).
    — An argument to a floating-point classification or comparison macro is not of real
      floating type (7.12.3, 7.12.14).
    — A macro definition of setjmp is suppressed in order to access an actual function, or
      the program defines an external identifier with the name setjmp (7.13).
    — An invocation of the setjmp macro occurs other than in an allowed context
      (7.13.2.1).
    — The longjmp function is invoked to restore a nonexistent environment (7.13.2.1).
    — After a longjmp, there is an attempt to access the value of an object of automatic
      storage duration that does not have volatile-qualified type, local to the function
      containing the invocation of the corresponding setjmp macro, that was changed
      between the setjmp invocation and longjmp call (7.13.2.1).
    — The program specifies an invalid pointer to a signal handler function (7.14.1.1).
    — A signal handler returns when the signal corresponded to a computational exception
      (7.14.1.1).
    — A signal handler called in response to SIGFPE, SIGILL, SIGSEGV, or any other
      implementation-defined value corresponding to a computational exception returns
      (7.14.1.1).
    — A signal occurs as the result of calling the abort or raise function, and the signal
      handler calls the raise function (7.14.1.1).
    — A signal occurs other than as the result of calling the abort or raise function, and
      the signal handler refers to an object with static or thread storage duration that is not a
      lock-free atomic object other than by assigning a value to an object declared as
      volatile sig_atomic_t, or calls any function in the standard library other
      than the abort function, the _Exit function, the quick_exit function, or the
      signal function (for the same signal number) (7.14.1.1).
    — The value of errno is referred to after a signal occurred other than as the result of
      calling the abort or raise function and the corresponding signal handler obtained
      a SIG_ERR return from a call to the signal function (7.14.1.1).
    — A signal is generated by an asynchronous signal handler (7.14.1.1).
    — The signal function is used in a multi-threaded program (7.14.1.1).
    — A function with a variable number of arguments attempts to access its varying
      arguments other than through a properly declared and initialized va_list object, or
      before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4).
    — The macro va_arg is invoked using the parameter ap that was passed to a function
      that invoked the macro va_arg with the same parameter (7.16).
    — A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in
      order to access an actual function, or the program defines an external identifier with
      the name va_copy or va_end (7.16.1).
    — The va_start or va_copy macro is invoked without a corresponding invocation
      of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3,
      7.16.1.4).
    — The type parameter to the va_arg macro is not such that a pointer to an object of
      that type can be obtained simply by postfixing a * (7.16.1.1).
    — The va_arg macro is invoked when there is no actual next argument, or with a
      specified type that is not compatible with the promoted type of the actual next
      argument, with certain exceptions (7.16.1.1).
    — The va_copy or va_start macro is called to initialize a va_list that was
      previously initialized by either macro without an intervening invocation of the
      va_end macro for the same va_list (7.16.1.2, 7.16.1.4).
    — The parameter parmN of a va_start macro is declared with the register
      storage class, with a function or array type, or with a type that is not compatible with
      the type that results after application of the default argument promotions (7.16.1.4).
    — The member designator parameter of an offsetof macro is an invalid right
      operand of the . operator for the type parameter, or designates a bit-field (7.19).
    — The argument in an instance of one of the integer-constant macros is not a decimal,
      octal, or hexadecimal constant, or it has a value that exceeds the limits for the
      corresponding type (7.20.4).
    — A byte input/output function is applied to a wide-oriented stream, or a wide character
      input/output function is applied to a byte-oriented stream (7.21.2).
    — Use is made of any portion of a file beyond the most recent wide character written to
      a wide-oriented stream (7.21.2).
    — The value of a pointer to a FILE object is used after the associated file is closed
      (7.21.3).
    — The stream for the fflush function points to an input stream or to an update stream
      in which the most recent operation was input (7.21.5.2).
    — The string pointed to by the mode argument in a call to the fopen function does not
      exactly match one of the specified character sequences (7.21.5.3).
    — An output operation on an update stream is followed by an input operation without an
      intervening call to the fflush function or a file positioning function, or an input
      operation on an update stream is followed by an output operation with an intervening
      call to a file positioning function (7.21.5.3).
    — An attempt is made to use the contents of the array that was supplied in a call to the
      setvbuf function (7.21.5.6).
    — There are insufficient arguments for the format in a call to one of the formatted
      input/output functions, or an argument does not have an appropriate type (7.21.6.1,
      7.21.6.2, 7.29.2.1, 7.29.2.2).
    — The format in a call to one of the formatted input/output functions or to the
      strftime or wcsftime function is not a valid multibyte character sequence that
      begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.27.3.5, 7.29.2.1, 7.29.2.2,
      7.29.5.1).
    — In a call to one of the formatted output functions, a precision appears with a
      conversion specifier other than those described (7.21.6.1, 7.29.2.1).
    — A conversion specification for a formatted output function uses an asterisk to denote
      an argument-supplied field width or precision, but the corresponding argument is not
      provided (7.21.6.1, 7.29.2.1).
    — A conversion specification for a formatted output function uses a # or 0 flag with a
      conversion specifier other than those described (7.21.6.1, 7.29.2.1).
    — A conversion specification for one of the formatted input/output functions uses a
      length modifier with a conversion specifier other than those described (7.21.6.1,
      7.21.6.2, 7.29.2.1, 7.29.2.2).
    — An s conversion specifier is encountered by one of the formatted output functions,
      and the argument is missing the null terminator (unless a precision is specified that
      does not require null termination) (7.21.6.1, 7.29.2.1).
    — An n conversion specification for one of the formatted input/output functions includes
      any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1,
      7.21.6.2, 7.29.2.1, 7.29.2.2).
    — A % conversion specifier is encountered by one of the formatted input/output
      functions, but the complete conversion specification is not exactly %% (7.21.6.1,
      7.21.6.2, 7.29.2.1, 7.29.2.2).
    — An invalid conversion specification is found in the format for one of the formatted
      input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2,
      7.27.3.5, 7.29.2.1, 7.29.2.2, 7.29.5.1).
    — The number of characters or wide characters transmitted by a formatted output
      function (or written to an array, or that would have been written to an array) is greater
      than INT_MAX (7.21.6.1, 7.29.2.1).
    — The number of input items assigned by a formatted input function is greater than
      INT_MAX (7.21.6.2, 7.29.2.2).
    — The result of a conversion by one of the formatted input functions cannot be
      represented in the corresponding object, or the receiving object does not have an
      appropriate type (7.21.6.2, 7.29.2.2).
    — A c, s, or [ conversion specifier is encountered by one of the formatted input
      functions, and the array pointed to by the corresponding argument is not large enough
      to accept the input sequence (and a null terminator if the conversion specifier is s or
      [) (7.21.6.2, 7.29.2.2).
    — A c, s, or [ conversion specifier with an l qualifier is encountered by one of the
      formatted input functions, but the input is not a valid multibyte character sequence
      that begins in the initial shift state (7.21.6.2, 7.29.2.2).
    — The input item for a %p conversion by one of the formatted input functions is not a
      value converted earlier during the same program execution (7.21.6.2, 7.29.2.2).
    — The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf,
      vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or
      vwscanf function is called with an improperly initialized va_list argument, or
      the argument is used (other than in an invocation of va_end) after the function
      returns (7.21.6.8, 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
      7.29.2.5, 7.29.2.6, 7.29.2.7, 7.29.2.8, 7.29.2.9, 7.29.2.10).
    — The contents of the array supplied in a call to the fgets or fgetws function are
      used after a read error occurred (7.21.7.2, 7.29.3.2).
    — The file position indicator for a binary stream is used after a call to the ungetc
      function where its value was zero before the call (7.21.7.10).
    — The file position indicator for a stream is used after an error occurred during a call to
      the fread or fwrite function (7.21.8.1, 7.21.8.2).
    — A partial element read by a call to the fread function is used (7.21.8.1).
    — The fseek function is called for a text stream with a nonzero offset and either the
      offset was not returned by a previous successful call to the ftell function on a
      stream associated with the same file or whence is not SEEK_SET (7.21.9.2).
    — The fsetpos function is called to set a position that was not returned by a previous
      successful call to the fgetpos function on a stream associated with the same file
      (7.21.9.3).
    — A non-null pointer returned by a call to the calloc, malloc, or realloc function
      with a zero requested size is used to access an object (7.22.3).
    — The value of a pointer that refers to space deallocated by a call to the free or
      realloc function is used (7.22.3).
    — The alignment requested of the aligned_alloc function is not valid or not
      supported by the implementation, or the size requested is not an integral multiple of
      the alignment (7.22.3.1).
    — The pointer argument to the free or realloc function does not match a pointer
      earlier returned by a memory management function, or the space has been deallocated
      by a call to free or realloc (7.22.3.3, 7.22.3.5).
    — The value of the object allocated by the malloc function is used (7.22.3.4).
    — The value of any bytes in a new object allocated by the realloc function beyond
      the size of the old object are used (7.22.3.5).
    — The program calls the exit or quick_exit function more than once, or calls both
      functions (7.22.4.4, 7.22.4.7).
    — During the call to a function registered with the atexit or at_quick_exit
      function, a call is made to the longjmp function that would terminate the call to the
      registered function (7.22.4.4, 7.22.4.7).
    — The string set up by the getenv or strerror function is modified by the program
      (7.22.4.6, 7.24.6.2).
    — A signal is raised while the quick_exit function is executing (7.22.4.7).
    — A command is executed through the system function in a way that is documented as
      causing termination or some other form of undefined behavior (7.22.4.8).
    — A searching or sorting utility function is called with an invalid pointer argument, even
      if the number of elements is zero (7.22.5).
    — The comparison function called by a searching or sorting utility function alters the
      contents of the array being searched or sorted, or returns ordering values
      inconsistently (7.22.5).
    — The array being searched by the bsearch function does not have its elements in
      proper order (7.22.5.1).
    — The current conversion state is used by a multibyte/wide character conversion
      function after changing the LC_CTYPE category (7.22.7).
    — A string or wide string utility function is instructed to access an array beyond the end
      of an object (7.24.1, 7.29.4).
    — A string or wide string utility function is called with an invalid pointer argument, even
      if the length is zero (7.24.1, 7.29.4).
    — The contents of the destination array are used after a call to the strxfrm,
      strftime, wcsxfrm, or wcsftime function in which the specified length was
      too small to hold the entire null-terminated result (7.24.4.5, 7.27.3.5, 7.29.4.4.4,
      7.29.5.1).
    — The first argument in the very first call to the strtok or wcstok is a null pointer
      (7.24.5.8, 7.29.4.5.7).
    — The type of an argument to a type-generic macro is not compatible with the type of
      the corresponding parameter of the selected function (7.25).
    — A complex argument is supplied for a generic parameter of a type-generic macro that
      has no corresponding complex function (7.25).
    — At least one member of the broken-down time passed to asctime contains a value
      outside its normal range, or the calculated year exceeds four digits or is less than the
      year 1000 (7.27.3.1).
    — The argument corresponding to an s specifier without an l qualifier in a call to the
      fwprintf function does not point to a valid multibyte character sequence that
      begins in the initial shift state (7.29.2.11).
    — In a call to the wcstok function, the object pointed to by ptr does not have the
      value stored by the previous call for the same wide string (7.29.4.5.7).
    — An mbstate_t object is used inappropriately (7.29.6).
    — The value of an argument of type wint_t to a wide character classification or case
      mapping function is neither equal to the value of WEOF nor representable as a
      wchar_t (7.30.1).
        — The iswctype function is called using a different LC_CTYPE category from the
          one in effect for the call to the wctype function that returned the description
          (7.30.2.2.1).
        — The towctrans function is called using a different LC_CTYPE category from the
          one in effect for the call to the wctrans function that returned the description
          (7.30.3.2.1).

### J.3 [Implementation-defined behavior]

    1   A conforming implementation is required to document its choice of behavior in each of
        the areas listed in this subclause. The following are implementation-defined:

### J.3.1 [Translation]

    1   — How a diagnostic is identified (3.10, 5.1.1.3).
        — Whether each nonempty sequence of white-space characters other than new-line is
          retained or replaced by one space character in translation phase 3 (5.1.1.2).

### J.3.2 [Environment]

    1   — The mapping between physical source file multibyte characters and the source
          character set in translation phase 1 (5.1.1.2).
        — The name and type of the function called at program startup in a freestanding
          environment (5.1.2.1).
        — The effect of program termination in a freestanding environment (5.1.2.1).
        — An alternative manner in which the main function may be defined (5.1.2.2.1).
        — The values given to the strings pointed to by the argv argument to main (5.1.2.2.1).
        — What constitutes an interactive device (5.1.2.3).
        — Whether a program can have more than one thread of execution in a freestanding
          environment (5.1.2.4).
        — The set of signals, their semantics, and their default handling (7.14).
        — Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a
          computational exception (7.14.1.1).
        — Signals for which the equivalent of signal(sig, SIG_IGN); is executed at
          program startup (7.14.1.1).
        — The set of environment names and the method for altering the environment list used
          by the getenv function (7.22.4.6).
        — The manner of execution of the string by the system function (7.22.4.8).

### J.3.3 [Identifiers]

    1   — Which additional multibyte characters may appear in identifiers and their
          correspondence to universal character names (6.4.2).
        — The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).

### J.3.4 [Characters]

    1   — The number of bits in a byte (3.6).
        — The values of the members of the execution character set (5.2.1).
        — The unique value of the member of the execution character set produced for each of
          the standard alphabetic escape sequences (5.2.2).
        — The value of a char object into which has been stored any character other than a
          member of the basic execution character set (6.2.5).
        — Which of signed char or unsigned char has the same range, representation,
          and behavior as ‘‘plain’’ char (6.2.5, 6.3.1.1).
        — The mapping of members of the source character set (in character constants and string
          literals) to members of the execution character set (6.4.4.4, 5.1.1.2).
        — The value of an integer character constant containing more than one character or
          containing a character or escape sequence that does not map to a single-byte
          execution character (6.4.4.4).
        — The value of a wide character constant containing more than one multibyte character
          or a single multibyte character that maps to multiple members of the extended
          execution character set, or containing a multibyte character or escape sequence not
          represented in the extended execution character set (6.4.4.4).
        — The current locale used to convert a wide character constant consisting of a single
          multibyte character that maps to a member of the extended execution character set
          into a corresponding wide character code (6.4.4.4).
        — Whether differently-prefixed wide string literal tokens can be concatenated and, if so,
          the treatment of the resulting multibyte character sequence (6.4.5).
        — The current locale used to convert a wide string literal into corresponding wide
          character codes (6.4.5).
        — The value of a string literal containing a multibyte character or escape sequence not
          represented in the execution character set (6.4.5).
        — The encoding of any of wchar_t, char16_t, and char32_t where the
          corresponding  standard   encoding macro      (_ _STDC_ISO_10646_ _,
          _ _STDC_UTF_16_ _, or _ _STDC_UTF_32_ _) is not defined (6.10.8.2).

### J.3.5 [Integers]

    1   — Any extended integer types that exist in the implementation (6.2.5).
        — Whether signed integer types are represented using sign and magnitude, two’s
          complement, or ones’ complement, and whether the extraordinary value is a trap
          representation or an ordinary value (6.2.6.2).
        — The rank of any extended integer type relative to another extended integer type with
          the same precision (6.3.1.1).
        — The result of, or the signal raised by, converting an integer to a signed integer type
          when the value cannot be represented in an object of that type (6.3.1.3).
        — The results of some bitwise operations on signed integers (6.5).

### J.3.6 [Floating point]

    1   — The accuracy of the floating-point operations and of the library functions in
          <math.h> and <complex.h> that return floating-point results (5.2.4.2.2).
        — The accuracy of the conversions between floating-point internal representations and
          string representations performed by the library functions in <stdio.h>,
          <stdlib.h>, and <wchar.h> (5.2.4.2.2).
        — The rounding behaviors characterized by non-standard values of FLT_ROUNDS
          (5.2.4.2.2).
        — The evaluation methods characterized by non-standard negative values of
          FLT_EVAL_METHOD (5.2.4.2.2).
        — The direction of rounding when an integer is converted to a floating-point number that
          cannot exactly represent the original value (6.3.1.4).
        — The direction of rounding when a floating-point number is converted to a narrower
          floating-point number (6.3.1.5).
        — How the nearest representable value or the larger or smaller representable value
          immediately adjacent to the nearest representable value is chosen for certain floating
          constants (6.4.4.2).
        — Whether and how floating expressions are contracted when not disallowed by the
          FP_CONTRACT pragma (6.5).
        — The default state for the FENV_ACCESS pragma (7.6.1).
        — Additional floating-point exceptions, rounding          modes,     environments,   and
          classifications, and their macro names (7.6, 7.12).
        — The default state for the FP_CONTRACT pragma (7.12.2).

### J.3.7 [Arrays and pointers]

    1   — The result of converting a pointer to an integer or vice versa (6.3.2.3).
        — The size of the result of subtracting two pointers to elements of the same array
          (6.5.6).

### J.3.8 [Hints]

    1   — The extent to which suggestions made by using the register storage-class
          specifier are effective (6.7.1).
        — The extent to which suggestions made by using the inline function specifier are
          effective (6.7.4).

### J.3.9 [Structures, unions, enumerations, and bit-fields]

    1   — Whether a ‘‘plain’’ int bit-field is treated as a signed int bit-field or as an
          unsigned int bit-field (6.7.2, 6.7.2.1).
        — Allowable bit-field types other than _Bool, signed int, and unsigned int
          (6.7.2.1).
        — Whether atomic types are permitted for bit-fields (6.7.2.1).
        — Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).
        — The order of allocation of bit-fields within a unit (6.7.2.1).
        — The alignment of non-bit-field members of structures (6.7.2.1). This should present
          no problem unless binary data written by one implementation is read by another.
        — The integer type compatible with each enumerated type (6.7.2.2).

### J.3.10 [Qualifiers]

    1   — What constitutes an access to an object that has volatile-qualified type (6.7.3).

### J.3.11 [Preprocessing directives]

    1   — The locations within #pragma directives where header name preprocessing tokens
          are recognized (6.4, 6.4.7).
        — How sequences in both forms of header names are mapped to headers or external
          source file names (6.4.7).
        — Whether the value of a character constant in a constant expression that controls
          conditional inclusion matches the value of the same character constant in the
          execution character set (6.10.1).
        — Whether the value of a single-character character constant in a constant expression
          that controls conditional inclusion may have a negative value (6.10.1).
        — The places that are searched for an included < > delimited header, and how the places
          are specified or the header is identified (6.10.2).
        — How the named source file is searched for in an included " " delimited header
          (6.10.2).
        — The method by which preprocessing tokens (possibly resulting from macro
          expansion) in a #include directive are combined into a header name (6.10.2).
        — The nesting limit for #include processing (6.10.2).
        — Whether the # operator inserts a \ character before the \ character that begins a
          universal character name in a character constant or string literal (6.10.3.2).
        — The behavior on each recognized non-STDC #pragma directive (6.10.6).
        — The definitions for _ _DATE_ _ and _ _TIME_ _ when respectively, the date and
          time of translation are not available (6.10.8.1).

### J.3.12 [Library functions]

    1   — Any library facilities available to a freestanding program, other than the minimal set
          required by clause 4 (5.1.2.1).
        — The format of the diagnostic printed by the assert macro (7.2.1.1).
        — The representation of the floating-point            status   flags   stored   by   the
          fegetexceptflag function (7.6.2.2).
        — Whether the feraiseexcept function raises the ‘‘inexact’’ floating-point
          exception in addition to the ‘‘overflow’’ or ‘‘underflow’’ floating-point exception
          (7.6.2.3).
        — Strings other than "C" and "" that may be passed as the second argument to the
          setlocale function (7.11.1.1).
        — The types defined for float_t and double_t when the value of the
          FLT_EVAL_METHOD macro is less than 0 (7.12).
        — Domain errors for the mathematics functions, other than those required by this
          International Standard (7.12.1).
        — The values returned by the mathematics functions on domain errors or pole errors
          (7.12.1).
        — The values returned by the mathematics functions on underflow range errors, whether
          errno is set to the value of the macro ERANGE when the integer expression
          math_errhandling & MATH_ERRNO is nonzero, and whether the ‘‘underflow’’
          floating-point exception is raised when the integer expression math_errhandling
          & MATH_ERREXCEPT is nonzero. (7.12.1).
    — Whether a domain error occurs or zero is returned when an fmod function has a
      second argument of zero (7.12.10.1).
    — Whether a domain error occurs or zero is returned when a remainder function has
      a second argument of zero (7.12.10.2).
    — The base-2 logarithm of the modulus used by the remquo functions in reducing the
      quotient (7.12.10.3).
    — Whether a domain error occurs or zero is returned when a remquo function has a
      second argument of zero (7.12.10.3).
    — Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call
      of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).
    — The null pointer constant to which the macro NULL expands (7.19).
    — Whether the last line of a text stream requires a terminating new-line character
      (7.21.2).
    — Whether space characters that are written out to a text stream immediately before a
      new-line character appear when read in (7.21.2).
    — The number of null characters that may be appended to data written to a binary
      stream (7.21.2).
    — Whether the file position indicator of an append-mode stream is initially positioned at
      the beginning or end of the file (7.21.3).
    — Whether a write on a text stream causes the associated file to be truncated beyond that
      point (7.21.3).
    — The characteristics of file buffering (7.21.3).
    — Whether a zero-length file actually exists (7.21.3).
    — The rules for composing valid file names (7.21.3).
    — Whether the same file can be simultaneously open multiple times (7.21.3).
    — The nature and choice of encodings used for multibyte characters in files (7.21.3).
    — The effect of the remove function on an open file (7.21.4.1).
    — The effect if a file with the new name exists prior to a call to the rename function
      (7.21.4.2).
    — Whether an open temporary file is removed upon abnormal program termination
      (7.21.4.3).
    — Which changes of mode are permitted (if any), and under what circumstances
      (7.21.5.4).
    — The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar
      sequence printed for a NaN (7.21.6.1, 7.29.2.1).
    — The output for %p conversion in the fprintf or fwprintf function (7.21.6.1,
      7.29.2.1).
    — The interpretation of a - character that is neither the first nor the last character, nor
      the second where a ^ character is the first, in the scanlist for %[ conversion in the
      fscanf or fwscanf function (7.21.6.2, 7.29.2.1).
    — The set of sequences matched by a %p conversion and the interpretation of the
      corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.29.2.2).
    — The value to which the macro errno is set by the fgetpos, fsetpos, or ftell
      functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4).
    — The meaning of any n-char or n-wchar sequence in a string representing a NaN that is
      converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold
      function (7.22.1.3, 7.29.4.1.1).
    — Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold
      function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.29.4.1.1).
    — Whether the calloc, malloc, and realloc functions return a null pointer or a
      pointer to an allocated object when the size requested is zero (7.22.3).
    — Whether open streams with unwritten buffered data are flushed, open streams are
      closed, or temporary files are removed when the abort or _Exit function is called
      (7.22.4.1, 7.22.4.5).
    — The termination status returned to the host environment by the abort, exit,
      _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7).
    — The value returned by the system function when its argument is not a null pointer
      (7.22.4.8).
    — The range and precision of times representable in clock_t and time_t (7.27).                ∗
    — The local time zone and Daylight Saving Time (7.27.1).
    — The era for the clock function (7.27.2.1).
    — The TIME_UTC epoch (7.27.2.5).
    — The replacement string for the %Z specifier to the strftime, and wcsftime
      functions in the "C" locale (7.27.3.5, 7.29.5.1).
    — Whether the functions in <math.h> honor the rounding direction mode in an
      IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10).

### J.3.13 [Architecture]

    1   — The values or expressions assigned to the macros specified in the headers
          <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.20.2, 7.20.3).
        — The result of attempting to indirectly access an object with automatic or thread
          storage duration from a thread other than the one with which it is associated (6.2.4).
        — The number, order, and encoding of bytes in any object (when not explicitly specified
          in this International Standard) (6.2.6.1).
        — Whether any extended alignments are supported and the contexts in which they are
          supported (6.2.8).
        — Valid alignment values other than those returned by an _Alignof expression for
          fundamental types, if any (6.2.8).
        — The value of the result of the sizeof and _Alignof operators (6.5.3.4).

### J.4 [Locale-specific behavior]

    1   The following characteristics of a hosted environment are locale-specific and are required
        to be documented by the implementation:
        — Additional members of the source and execution character sets beyond the basic
          character set (5.2.1).
        — The presence, meaning, and representation of additional multibyte characters in the
          execution character set beyond the basic character set (5.2.1.2).
        — The shift states used for the encoding of multibyte characters (5.2.1.2).
        — The direction of writing of successive printing characters (5.2.2).
        — The decimal-point character (7.1.1).
        — The set of printing characters (7.4, 7.30.2).
        — The set of control characters (7.4, 7.30.2).
        — The sets of characters tested for by the isalpha, isblank, islower, ispunct,
          isspace, isupper, iswalpha, iswblank, iswlower, iswpunct,
          iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10,
          7.4.1.11, 7.30.2.1.2, 7.30.2.1.3, 7.30.2.1.7, 7.30.2.1.9, 7.30.2.1.10, 7.30.2.1.11).
        — The native environment (7.11.1.1).
        — Additional subject sequences accepted by the numeric conversion functions (7.22.1,
          7.29.4.1).
        — The collation sequence of the execution character set (7.24.4.3, 7.29.4.4.2).
        — The contents of the error message strings set up by the strerror function
          (7.24.6.2).
        — The formats for time and date (7.27.3.5, 7.29.5.1).
        — Character mappings that are supported by the towctrans function (7.30.1).
        — Character classifications that are supported by the iswctype function (7.30.1).

### J.5 [Common extensions]

    1   The following extensions are widely used in many systems, but are not portable to all
        implementations. The inclusion of any extension that may cause a strictly conforming
        program to become invalid renders an implementation nonconforming. Examples of such
        extensions are new keywords, extra library functions declared in standard headers, or
        predefined macros with names that do not begin with an underscore.

### J.5.1 [Environment arguments]

    1   In a hosted environment, the main function receives a third argument, char *envp[],
        that points to a null-terminated array of pointers to char, each of which points to a string
        that provides information about the environment for this execution of the program
        (5.1.2.2.1).

### J.5.2 [Specialized identifiers]

    1   Characters other than the underscore _, letters, and digits, that are not part of the basic
        source character set (such as the dollar sign $, or characters in national character sets)
        may appear in an identifier (6.4.2).

### J.5.3 [Lengths and cases of identifiers]

    1   All characters in identifiers (with or without external linkage) are significant (6.4.2).

### J.5.4 [Scopes of identifiers]

    1   A function identifier, or the identifier of an object the declaration of which contains the
        keyword extern, has file scope (6.2.1).

### J.5.5 [Writable string literals]

    1   String literals are modifiable (in which case, identical string literals should denote distinct
        objects) (6.4.5).

### J.5.6 [Other arithmetic types]

    1   Additional arithmetic types, such as _ _int128 or double double, and their
        appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have
        more range or precision than long double, may be used for evaluating expressions of
        other floating types, and may be used to define float_t or double_t. Additional
        floating types may also have less range or precision than float.

### J.5.7 [Function pointer casts]

    1   A pointer to an object or to void may be cast to a pointer to a function, allowing data to
        be invoked as a function (6.5.4).

    2   A pointer to a function may be cast to a pointer to an object or to void, allowing a
        function to be inspected or modified (for example, by a debugger) (6.5.4).

### J.5.8 [Extended bit-field types]

    1   A bit-field may be declared with a type other than _Bool, unsigned int, or
        signed int, with an appropriate maximum width (6.7.2.1).

### J.5.9 [The fortran keyword]

    1   The fortran function specifier may be used in a function declaration to indicate that
        calls suitable for FORTRAN should be generated, or that a different representation for the
        external name is to be generated (6.7.4).

### J.5.10 [The asm keyword]

    1   The asm keyword may be used to insert assembly language directly into the translator
        output (6.8). The most common implementation is via a statement of the form:
               asm ( character-string-literal );

### J.5.11 [Multiple external definitions]

    1   There may be more than one external definition for the identifier of an object, with or
        without the explicit use of the keyword extern; if the definitions disagree, or more than
        one is initialized, the behavior is undefined (6.9.2).

### J.5.12 [Predefined macro names]

    1   Macro names that do not begin with an underscore, describing the translation and
        execution environments, are defined by the implementation before translation begins
        (6.10.8).

### J.5.13 [Floating-point status flags]

    1   If any floating-point status flags are set on normal termination after all calls to functions
        registered by the atexit function have been made (see 7.22.4.4), the implementation
        writes some diagnostics indicating the fact to the stderr stream, if it is still open,

### J.5.14 [Extra arguments for signal handlers]

    1   Handlers for specific signals are called with extra arguments in addition to the signal
        number (7.14.1.1).

### J.5.15 [Additional stream types and file-opening modes]

    1   Additional mappings from files to streams are supported (7.21.2).

    2   Additional file-opening modes may be specified by characters appended to the mode
        argument of the fopen function (7.21.5.3).

### J.5.16 [Defined file position indicator]

    1   The file position indicator is decremented by each successful call to the ungetc or
        ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10,
        7.29.3.10).

### J.5.17 [Math error reporting]

    1   Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors
        instead of, or in addition to, setting errno or raising floating-point exceptions (7.3,
        7.12).

### K. [Annex K (normative) Bounds-checking interfaces]

### K.1 [Background]

    1   Traditionally, the C Library has contained many functions that trust the programmer to
        provide output character arrays big enough to hold the result being produced. Not only
        do these functions not check that the arrays are big enough, they frequently lack the
        information needed to perform such checks. While it is possible to write safe, robust, and
        error-free code using the existing library, the library tends to promote programming styles
        that lead to mysterious failures if a result is too big for the provided array.

    2   A common programming style is to declare character arrays large enough to handle most
        practical cases. However, if these arrays are not large enough to handle the resulting
        strings, data can be written past the end of the array overwriting other data and program
        structures. The program never gets any indication that a problem exists, and so never has
        a chance to recover or to fail gracefully.

    3   Worse, this style of programming has compromised the security of computers and
        networks. Buffer overflows can often be exploited to run arbitrary code with the
        permissions of the vulnerable (defective) program.

    4   If the programmer writes runtime checks to verify lengths before calling library
        functions, then those runtime checks frequently duplicate work done inside the library
        functions, which discover string lengths as a side effect of doing their job.

    5   This annex provides alternative library functions that promote safer, more secure
        programming. The alternative functions verify that output buffers are large enough for
        the intended result and return a failure indicator if they are not. Data is never written past
        the end of an array. All string results are null terminated.

    6   This annex also addresses another problem that complicates writing robust code:
        functions that are not reentrant because they return pointers to static objects owned by the
        function. Such functions can be troublesome since a previously returned result can
        change if the function is called again, perhaps by another thread.

### K.2 [Scope]

    1   This annex specifies a series of optional extensions that can be useful in the mitigation of
        security vulnerabilities in programs, and comprise new functions, macros, and types
        declared or defined in existing standard headers.

    2   An implementation that defines _ _STDC_LIB_EXT1_ _ shall conform to the
        specifications in this annex.[380]

    Footnote 380) Implementations that do not define _ _STDC_LIB_EXT1_ _ are not required to conform to these
             specifications.

    3   Subclause K.3 should be read as if it were merged into the parallel structure of named
        subclauses of clause 7.

### K.3 [Library]

### K.3.1 [Introduction]

### K.3.1.1 [Standard headers]

    1   The functions, macros, and types declared or defined in K.3 and its subclauses are not
        declared or defined by their respective headers if _ _STDC_WANT_LIB_EXT1_ _ is
        defined as a macro which expands to the integer constant 0 at the point in the source file
        where the appropriate header is first included.

    2   The functions, macros, and types declared or defined in K.3 and its subclauses are
        declared and defined by their respective headers if _ _STDC_WANT_LIB_EXT1_ _ is
        defined as a macro which expands to the integer constant 1 at the point in the source file
        where the appropriate header is first included.[381]

    Footnote 381) Future revisions of this International Standard may define meanings for other values of
             _ _STDC_WANT_LIB_EXT1_ _.

    3   It is implementation-defined whether the functions, macros, and types declared or defined
        in K.3 and its subclauses are declared or defined by their respective headers if
        _ _STDC_WANT_LIB_EXT1_ _ is not defined as a macro at the point in the source file
        where the appropriate header is first included.[382]

    Footnote 382) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in
             headers. All other names are not reserved, and a conforming implementation is not permitted to use
             them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an
             unreserved name is defined in a header when _ _STDC_WANT_LIB_EXT1_ _ is defined as 0, the
             implementation is not conforming.

    4   Within a preprocessing translation unit, _ _STDC_WANT_LIB_EXT1_ _ shall be
        defined identically for all inclusions of any headers from subclause K.3. If
        _ _STDC_WANT_LIB_EXT1_ _ is defined differently for any such inclusion, the
        implementation shall issue a diagnostic as if a preprocessor error directive were used.

### K.3.1.2 [Reserved identifiers]

    1   Each macro name in any of the following subclauses is reserved for use as specified if it
        is defined by any of its associated headers when included; unless explicitly stated
        otherwise (see 7.1.4).

    2   All identifiers with external linkage in any of the following subclauses are reserved for
        use as identifiers with external linkage if any of them are used by the program. None of
        them are reserved if none of them are used.

    3   Each identifier with file scope listed in any of the following subclauses is reserved for use
        as a macro name and as an identifier with file scope in the same name space if it is
        defined by any of its associated headers when included.

### K.3.1.3 [Use of errno]

    1   An implementation may set errno for the functions defined in this annex, but is not
        required to.

### K.3.1.4 [Runtime-constraint violations]

    1   Most functions in this annex include as part of their specification a list of runtime-
        constraints. These runtime-constraints are requirements on the program using the
        library.[383]

    Footnote 383) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still
             exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a
             runtime-constraint violation by calling the runtime-constraint handler. This license comes directly
             from the definition of undefined behavior.

    2   Implementations shall verify that the runtime-constraints for a function are not violated
        by the program. If a runtime-constraint is violated, the implementation shall call the
        currently registered runtime-constraint handler (see set_constraint_handler_s
        in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library
        function result in only one call to the runtime-constraint handler. It is unspecified which
        one of the multiple runtime-constraint violations cause the handler to be called.

    3   If the runtime-constraints section for a function states an action to be performed when a
        runtime-constraint violation occurs, the function shall perform the action before calling
        the runtime-constraint handler. If the runtime-constraints section lists actions that are
        prohibited when a runtime-constraint violation occurs, then such actions are prohibited to
        the function both before calling the handler and after the handler returns.

    4   The runtime-constraint handler might not return. If the handler does return, the library
        function whose runtime-constraint was violated shall return some indication of failure as
        given by the returns section in the function’s specification.

### K.3.2 [Errors <errno.h>]

    1   The header <errno.h> defines a type.

    2   The type is
                errno_t
        which is type int.[384]

    Footnote 384) As a matter of programming style, errno_t may be used as the type of something that deals only
             with the values that might be found in errno. For example, a function which returns the value of
             errno might be declared as having the return type errno_t.

### K.3.3 [Common definitions <stddef.h>]

    1   The header <stddef.h> defines a type.

    2   The type is
                rsize_t
        which is the type size_t.[385]

    Footnote 385) See the description of the RSIZE_MAX macro in <stdint.h>.

### K.3.4 [Integer types <stdint.h>]

    1   The header <stdint.h> defines a macro.

    2   The macro is
                RSIZE_MAX
        which expands to a value[386] of type size_t. Functions that have parameters of type
        rsize_t consider it a runtime-constraint violation if the values of those parameters are
        greater than RSIZE_MAX.
        Recommended practice

    Footnote 386) The macro RSIZE_MAX need not expand to a constant expression.

    3   Extremely large object sizes are frequently a sign that an object’s size was calculated
        incorrectly. For example, negative numbers appear as very large positive numbers when
        converted to an unsigned type like size_t. Also, some implementations do not support
        objects as large as the maximum value that can be represented by type size_t.

    4   For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect
        programming errors. For implementations targeting machines with large address spaces,
        it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest
        object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of
        some legitimate, but very large, objects. Implementations targeting machines with small
        address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there
        is no object size that is considered a runtime-constraint violation.

### K.3.5 [Input/output <stdio.h>]

    1   The header <stdio.h> defines several macros and two types.

    2   The macros are
               L_tmpnam_s
        which expands to an integer constant expression that is the size needed for an array of
        char large enough to hold a temporary file name string generated by the tmpnam_s
        function;
               TMP_MAX_S
        which expands to an integer constant expression that is the maximum number of unique
        file names that can be generated by the tmpnam_s function.

    3   The types are
               errno_t
        which is type int; and
               rsize_t
        which is the type size_t.

### K.3.5.1 [Operations on files]

### K.3.5.1.1 [The tmpfile_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdio.h>
               errno_t tmpfile_s(FILE * restrict * restrict streamptr);
        Runtime-constraints

    2   streamptr shall not be a null pointer.

    3   If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file.
        Description

    4   The tmpfile_s function creates a temporary binary file that is different from any other
        existing file and that will automatically be removed when it is closed or at program
        termination. If the program terminates abnormally, whether an open temporary file is
        removed is implementation-defined. The file is opened for update with "wb+" mode
        with the meaning that mode has in the fopen_s function (including the mode’s effect
        on exclusive access and file permissions).

    5   If the file was created successfully, then the pointer to FILE pointed to by streamptr
        will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
        to FILE pointed to by streamptr will be set to a null pointer.
        Recommended practice
        It should be possible to open at least TMP_MAX_S temporary files during the lifetime of
        the program (this limit may be shared with tmpnam_s) and there should be no limit on
        the number simultaneously open other than this limit and any limit on the number of open
        files (FOPEN_MAX).
        Returns

    6   The tmpfile_s function returns zero if it created the file. If it did not create the file or
        there was a runtime-constraint violation, tmpfile_s returns a nonzero value.

### K.3.5.1.2 [The tmpnam_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdio.h>
                errno_t tmpnam_s(char *s, rsize_t maxsize);
        Runtime-constraints

    2   s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX.
        maxsize shall be greater than the length of the generated file name string.
        Description

    3   The tmpnam_s function generates a string that is a valid file name and that is not the
        same as the name of an existing file.[387] The function is potentially capable of generating
        TMP_MAX_S different strings, but any or all of them may already be in use by existing
        files and thus not be suitable return values. The lengths of these strings shall be less than
        the value of the L_tmpnam_s macro.

    Footnote 387) Files created using strings generated by the tmpnam_s function are temporary only in the sense that
             their names should not collide with those generated by conventional naming rules for the
             implementation. It is still necessary to use the remove function to remove such files when their use
             is ended, and before program termination. Implementations should take care in choosing the patterns
             used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the
             race condition and possible conflict when multiple programs run simultaneously by the same user
             generate the same temporary file names.

    4   The tmpnam_s function generates a different string each time it is called.

    5   It is assumed that s points to an array of at least maxsize characters. This array will be
        set to generated string, as specified below.

    6    The implementation shall behave as if no library function except tmpnam calls the
         tmpnam_s function.[388]
         Recommended practice

    Footnote 388) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming
              convention for temporary files), but this is not required.

    7    After a program obtains a file name using the tmpnam_s function and before the
         program creates a file with that name, the possibility exists that someone else may create
         a file with that same name. To avoid this race condition, the tmpfile_s function
         should be used instead of tmpnam_s when possible. One situation that requires the use
         of the tmpnam_s function is when the program needs to create a temporary directory
         rather than a temporary file.
         Returns

    8    If no suitable string can be generated, or if there is a runtime-constraint violation, the
         tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize
         is greater than zero) and returns a nonzero value.

    9    Otherwise, the tmpnam_s function writes the string in the array pointed to by s and
         returns zero.
         Environmental limits

    10   The value of the macro TMP_MAX_S shall be at least 25.

### K.3.5.2 [File access functions]

### K.3.5.2.1 [The fopen_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdio.h>
                errno_t fopen_s(FILE * restrict * restrict streamptr,
                     const char * restrict filename,
                     const char * restrict mode);
         Runtime-constraints

    2    None of streamptr, filename, or mode shall be a null pointer.

    3    If there is a runtime-constraint violation, fopen_s does not attempt to open a file.
         Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the
         null pointer.
        Description

    4   The fopen_s function opens the file whose name is the string pointed to by
        filename, and associates a stream with it.

    5   The mode string shall be as described for fopen, with the addition that modes starting
        with the character 'w' or 'a' may be preceded by the character 'u', see below:
        uw             truncate to zero length or create text file for writing, default
                       permissions
        uwx            create text file for writing, default permissions
        ua             append; open or create text file for writing at end-of-file, default
                       permissions
        uwb            truncate to zero length or create binary file for writing, default
                       permissions
        uwbx           create binary file for writing, default permissions
        uab            append; open or create binary file for writing at end-of-file, default
                       permissions
        uw+            truncate to zero length or create text file for update, default
                       permissions
        uw+x           create text file for update, default permissions
        ua+            append; open or create text file for update, writing at end-of-file,
                       default permissions
        uw+b or uwb+   truncate to zero length or create binary file for update, default
                       permissions
        uw+bx or uwb+x create binary file for update, default permissions
        ua+b or uab+   append; open or create binary file for update, writing at end-of-file,
                       default permissions

    6   Opening a file with exclusive mode ('x' as the last character in the mode argument)
        fails if the file already exists or cannot be created.

    7   To the extent that the underlying system supports the concepts, files opened for writing
        shall be opened with exclusive (also known as non-shared) access. If the file is being
        created, and the first character of the mode string is not 'u', to the extent that the
        underlying system supports it, the file shall have a file permission that prevents other
        users on the system from accessing the file. If the file is being created and first character
        of the mode string is 'u', then by the time the file has been closed, it shall have the
        system default file access permissions.[389]

    Footnote 389) These are the same permissions that the file would have been created with by fopen.

    8   If the file was opened successfully, then the pointer to FILE pointed to by streamptr
        will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
        to FILE pointed to by streamptr will be set to a null pointer.
        Returns

    9   The fopen_s function returns zero if it opened the file. If it did not open the file or if
        there was a runtime-constraint violation, fopen_s returns a nonzero value.

### K.3.5.2.2 [The freopen_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdio.h>
               errno_t freopen_s(FILE * restrict * restrict newstreamptr,
                    const char * restrict filename,
                    const char * restrict mode,
                    FILE * restrict stream);
        Runtime-constraints

    2   None of newstreamptr, mode, and stream shall be a null pointer.

    3   If there is a runtime-constraint violation, freopen_s neither attempts to close any file
        associated with stream nor attempts to open a file. Furthermore, if newstreamptr is
        not a null pointer, fopen_s sets *newstreamptr to the null pointer.
        Description

    4   The freopen_s function opens the file whose name is the string pointed to by
        filename and associates the stream pointed to by stream with it. The mode
        argument has the same meaning as in the fopen_s function (including the mode’s effect
        on exclusive access and file permissions).

    5   If filename is a null pointer, the freopen_s function attempts to change the mode of
        the stream to that specified by mode, as if the name of the file currently associated with
        the stream had been used. It is implementation-defined which changes of mode are
        permitted (if any), and under what circumstances.

    6   The freopen_s function first attempts to close any file that is associated with stream.
        Failure to close the file is ignored. The error and end-of-file indicators for the stream are
        cleared.

    7   If the file was opened successfully, then the pointer to FILE pointed to by
        newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE
        pointed to by newstreamptr will be set to a null pointer.
        Returns

    8   The freopen_s function returns zero if it opened the file. If it did not open the file or
        there was a runtime-constraint violation, freopen_s returns a nonzero value.

### K.3.5.3 [Formatted input/output functions]

    1   Unless explicitly stated otherwise, if the execution of a function described in this
        subclause causes copying to take place between objects that overlap, the objects take on
        unspecified values.

### K.3.5.3.1 [The fprintf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdio.h>
                 int fprintf_s(FILE * restrict stream,
                      const char * restrict format, ...);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. The %n specifier[390] (modified or
        not by flags, field width, or precision) shall not appear in the string pointed to by
        format. Any argument to fprintf_s corresponding to a %s specifier shall not be a
        null pointer.

    Footnote 390) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation,[391] the fprintf_s function does not attempt
        to produce further output, and it is unspecified to what extent fprintf_s produced
        output before discovering the runtime-constraint violation.
        Description

    Footnote 391) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
             implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
             constraint violation.

    4   The fprintf_s function is equivalent to the fprintf function except for the explicit
        runtime-constraints listed above.
        Returns

    5   The fprintf_s function returns the number of characters transmitted, or a negative
        value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.5.3.2 [The fscanf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdio.h>
                int fscanf_s(FILE * restrict stream,
                     const char * restrict format, ...);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. Any argument indirected though in
        order to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation,[392] the fscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent fscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    Footnote 392) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
             implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
             constraint violation.

    4   The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion
        specifiers apply to a pair of arguments (unless assignment suppression is indicated by a
        *). The first of these arguments is the same as for fscanf. That argument is
        immediately followed in the argument list by the second argument, which has type
        rsize_t and gives the number of elements in the array pointed to by the first argument
        of the pair. If the first argument points to a scalar object, it is considered to be an array of
        one element.[393]

    Footnote 393) If the format is known at translation time, an implementation may issue a diagnostic for any argument
             used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
             argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
             the format is not known at translation time. For example, an implementation may issue a diagnostic
             for each argument after format that has of type pointer to one of char, signed char,
             unsigned char, or void that is not followed by an argument of a type compatible with
             rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
             using the hh length modifier, a length argument must follow the pointer argument. Another useful
             diagnostic could flag any non-pointer argument following format that did not have a type
             compatible with rsize_t.

    5   A matching failure occurs if the number of elements in a receiving object is insufficient to
        hold the converted input (including any trailing null character).
        Returns

    6   The fscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        fscanf_s function returns the number of input items assigned, which can be fewer than
        provided for, or even zero, in the event of an early matching failure.

    7   EXAMPLE 1        The call:
                 #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdio.h>
                 /* ... */
                 int n, i; float x; char name[50];
                 n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50);
        with the input line:
                 25 54.32E-1 thompson
        will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
        thompson\0.

    8   EXAMPLE 2        The call:
                 #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdio.h>
                 /* ... */
                 int n; char s[5];
                 n = fscanf_s(stdin, "%s", s, sizeof s);
        with the input line:
                 hello
        will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an
        array of six characters to store it.

### K.3.5.3.3 [The printf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdio.h>
                 int printf_s(const char * restrict format, ...);
        Runtime-constraints

    2   format shall not be a null pointer. The %n specifier[394] (modified or not by flags, field
        width, or precision) shall not appear in the string pointed to by format. Any argument
        to printf_s corresponding to a %s specifier shall not be a null pointer.

    Footnote 394) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, the printf_s function does not attempt to
        produce further output, and it is unspecified to what extent printf_s produced output
        before discovering the runtime-constraint violation.
        Description

    4   The printf_s function is equivalent to the printf function except for the explicit
        runtime-constraints listed above.
        Returns

    5   The printf_s function returns the number of characters transmitted, or a negative
        value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.5.3.4 [The scanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdio.h>
               int scanf_s(const char * restrict format, ...);
        Runtime-constraints

    2   format shall not be a null pointer. Any argument indirected though in order to store
        converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the scanf_s function does not attempt to
        perform further input, and it is unspecified to what extent scanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The scanf_s function is equivalent to fscanf_s with the argument stdin
        interposed before the arguments to scanf_s.
        Returns

    5   The scanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        scanf_s function returns the number of input items assigned, which can be fewer than
        provided for, or even zero, in the event of an early matching failure.

### K.3.5.3.5 [The snprintf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdio.h>
               int snprintf_s(char * restrict s, rsize_t n,
                    const char * restrict format, ...);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The %n specifier[395] (modified or not by flags, field width, or
        precision) shall not appear in the string pointed to by format. Any argument to
        snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
        error shall occur.

    Footnote 395) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the
        null character.
        Description

    4   The snprintf_s function is equivalent to the snprintf function except for the
        explicit runtime-constraints listed above.

    5   The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the
        array pointed to by s.
        Returns

    6   The snprintf_s function returns the number of characters that would have been
        written had n been sufficiently large, not counting the terminating null character, or a
        negative value if a runtime-constraint violation occurred. Thus, the null-terminated
        output has been completely written if and only if the returned value is nonnegative and
        less than n.

### K.3.5.3.6 [The sprintf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdio.h>
                 int sprintf_s(char * restrict s, rsize_t n,
                      const char * restrict format, ...);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The number of characters (including the trailing null) required for the
        result to be written to the array pointed to by s shall not be greater than n. The %n
        specifier[396] (modified or not by flags, field width, or precision) shall not appear in the
        string pointed to by format. Any argument to sprintf_s corresponding to a %s
        specifier shall not be a null pointer. No encoding error shall occur.

    Footnote 396) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the
        null character.
        Description

    4   The sprintf_s function is equivalent to the sprintf function except for the
        parameter n and the explicit runtime-constraints listed above.

    5   The sprintf_s function, unlike snprintf_s, treats a result too big for the array
        pointed to by s as a runtime-constraint violation.
        Returns

    6   If no runtime-constraint violation occurred, the sprintf_s function returns the number
        of characters written in the array, not counting the terminating null character. If an
        encoding error occurred, sprintf_s returns a negative value. If any other runtime-
        constraint violation occurred, sprintf_s returns zero.

### K.3.5.3.7 [The sscanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdio.h>
               int sscanf_s(const char * restrict s,
                    const char * restrict format, ...);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. Any argument indirected though in order
        to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the sscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent sscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The sscanf_s function is equivalent to fscanf_s, except that input is obtained from
        a string (specified by the argument s) rather than from a stream. Reaching the end of the
        string is equivalent to encountering end-of-file for the fscanf_s function. If copying
        takes place between objects that overlap, the objects take on unspecified values.
        Returns

    5   The sscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        sscanf_s function returns the number of input items assigned, which can be fewer than
        provided for, or even zero, in the event of an early matching failure.

### K.3.5.3.8 [The vfprintf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdarg.h>
                 #include <stdio.h>
                 int vfprintf_s(FILE * restrict stream,
                      const char * restrict format,
                      va_list arg);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. The %n specifier[397] (modified or
        not by flags, field width, or precision) shall not appear in the string pointed to by
        format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a
        null pointer.

    Footnote 397) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, the vfprintf_s function does not attempt to
        produce further output, and it is unspecified to what extent vfprintf_s produced
        output before discovering the runtime-constraint violation.
        Description

    4   The vfprintf_s function is equivalent to the vfprintf function except for the
        explicit runtime-constraints listed above.
        Returns

    5   The vfprintf_s function returns the number of characters transmitted, or a negative
        value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.5.3.9 [The vfscanf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdarg.h>
                 #include <stdio.h>
                 int vfscanf_s(FILE * restrict stream,
                      const char * restrict format,
                      va_list arg);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. Any argument indirected though in
        order to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the vfscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent vfscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The vfscanf_s function is equivalent to fscanf_s, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vfscanf_s function does not invoke the
        va_end macro.[398]
        Returns

    Footnote 398) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
             vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
             indeterminate.

    5   The vfscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        vfscanf_s function returns the number of input items assigned, which can be fewer
        than provided for, or even zero, in the event of an early matching failure.

### K.3.5.3.10 [The vprintf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdarg.h>
                 #include <stdio.h>
                 int vprintf_s(const char * restrict format,
                      va_list arg);
        Runtime-constraints

    2   format shall not be a null pointer. The %n specifier[399] (modified or not by flags, field
        width, or precision) shall not appear in the string pointed to by format. Any argument
        to vprintf_s corresponding to a %s specifier shall not be a null pointer.

    Footnote 399) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, the vprintf_s function does not attempt to
        produce further output, and it is unspecified to what extent vprintf_s produced output
        before discovering the runtime-constraint violation.
        Description

    4   The vprintf_s function is equivalent to the vprintf function except for the explicit
        runtime-constraints listed above.
        Returns

    5   The vprintf_s function returns the number of characters transmitted, or a negative
        value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.5.3.11 [The vscanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdarg.h>
               #include <stdio.h>
               int vscanf_s(const char * restrict format,
                    va_list arg);
        Runtime-constraints

    2   format shall not be a null pointer. Any argument indirected though in order to store
        converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the vscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent vscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The vscanf_s function is equivalent to scanf_s, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vscanf_s function does not invoke the
        va_end macro.[400]
        Returns

    Footnote 400) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
             vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
             indeterminate.

    5   The vscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        vscanf_s function returns the number of input items assigned, which can be fewer than
        provided for, or even zero, in the event of an early matching failure.

### K.3.5.3.12 [The vsnprintf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdarg.h>
                 #include <stdio.h>
                 int vsnprintf_s(char * restrict s, rsize_t n,
                      const char * restrict format,
                      va_list arg);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The %n specifier[401] (modified or not by flags, field width, or
        precision) shall not appear in the string pointed to by format. Any argument to
        vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
        error shall occur.

    Footnote 401) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the
        null character.
        Description

    4   The vsnprintf_s function is equivalent to the vsnprintf function except for the
        explicit runtime-constraints listed above.

    5   The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within
        the array pointed to by s.
        Returns

    6   The vsnprintf_s function returns the number of characters that would have been
        written had n been sufficiently large, not counting the terminating null character, or a
        negative value if a runtime-constraint violation occurred. Thus, the null-terminated
        output has been completely written if and only if the returned value is nonnegative and
        less than n.

### K.3.5.3.13 [The vsprintf_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdarg.h>
                 #include <stdio.h>
                 int vsprintf_s(char * restrict s, rsize_t n,
                      const char * restrict format,
                      va_list arg);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The number of characters (including the trailing null) required for the
        result to be written to the array pointed to by s shall not be greater than n. The %n
        specifier[402] (modified or not by flags, field width, or precision) shall not appear in the
        string pointed to by format. Any argument to vsprintf_s corresponding to a %s
        specifier shall not be a null pointer. No encoding error shall occur.

    Footnote 402) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
             at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
             format string was %%n.

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the
        null character.
        Description

    4   The vsprintf_s function is equivalent to the vsprintf function except for the
        parameter n and the explicit runtime-constraints listed above.

    5   The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array
        pointed to by s as a runtime-constraint violation.
        Returns

    6   If no runtime-constraint violation occurred, the vsprintf_s function returns the
        number of characters written in the array, not counting the terminating null character. If
        an encoding error occurred, vsprintf_s returns a negative value. If any other
        runtime-constraint violation occurred, vsprintf_s returns zero.

### K.3.5.3.14 [The vsscanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdarg.h>
               #include <stdio.h>
               int vsscanf_s(const char * restrict s,
                    const char * restrict format,
                    va_list arg);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. Any argument indirected though in order
        to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the vsscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent vsscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The vsscanf_s function is equivalent to sscanf_s, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vsscanf_s function does not invoke the
        va_end macro.[403]
        Returns

    Footnote 403) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
             vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
             indeterminate.

    5   The vsscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        vscanf_s function returns the number of input items assigned, which can be fewer than
        provided for, or even zero, in the event of an early matching failure.

### K.3.5.4 [Character input/output functions]

### K.3.5.4.1 [The gets_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdio.h>
               char *gets_s(char *s, rsize_t n);
        Runtime-constraints

    2   s shall not be a null pointer. n shall neither be equal to zero nor be greater than
        RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading
        n-1 characters from stdin.[404]

    Footnote 404) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for
             a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a
             one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets
             expect such a relationship.

    3   If there is a runtime-constraint violation, s[0] is set to the null character, and characters
        are read and discarded from stdin until a new-line character is read, or end-of-file or a
        read error occurs.
        Description

    4   The gets_s function reads at most one less than the number of characters specified by n
        from the stream pointed to by stdin, into the array pointed to by s. No additional
        characters are read after a new-line character (which is discarded) or after end-of-file.
        The discarded new-line character does not count towards number of characters read. A
        null character is written immediately after the last character read into the array.

    5   If end-of-file is encountered and no characters have been read into the array, or if a read
        error occurs during the operation, then s[0] is set to the null character, and the other
        elements of s take unspecified values.
        Recommended practice

    6   The fgets function allows properly-written programs to safely process input lines too
        long to store in the result array. In general this requires that callers of fgets pay
        attention to the presence or absence of a new-line character in the result array. Consider
        using fgets (along with any needed processing based on new-line characters) instead of
        gets_s.
        Returns

    7   The gets_s function returns s if successful. If there was a runtime-constraint violation,
        or if end-of-file is encountered and no characters have been read into the array, or if a
        read error occurs during the operation, then a null pointer is returned.

### K.3.6 [General utilities <stdlib.h>]

    1   The header <stdlib.h> defines three types.

    2   The types are
                errno_t
        which is type int; and
                rsize_t
        which is the type size_t; and
                constraint_handler_t
        which has the following definition
                typedef void (*constraint_handler_t)(
                     const char * restrict msg,
                     void * restrict ptr,
                     errno_t error);

### K.3.6.1 [Runtime-constraint handling]

### K.3.6.1.1 [The set_constraint_handler_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdlib.h>
                constraint_handler_t set_constraint_handler_s(
                     constraint_handler_t handler);
        Description

    2   The set_constraint_handler_s function sets the runtime-constraint handler to
        be handler. The runtime-constraint handler is the function to be called when a library
        function detects a runtime-constraint violation. Only the most recent handler registered
        with set_constraint_handler_s is called when a runtime-constraint violation
        occurs.

    3   When the handler is called, it is passed the following arguments in the following order:
           1.   A pointer to a character string describing the runtime-constraint violation.
           2.   A null pointer or a pointer to an implementation defined object.
           3.   If the function calling the handler has a return type declared as errno_t, the
                return value of the function is passed. Otherwise, a positive value of type
                errno_t is passed.

    4   The implementation has a default constraint handler that is used if no calls to the
        set_constraint_handler_s function have been made. The behavior of the
        default handler is implementation-defined, and it may cause the program to exit or abort.

    5   If the handler argument to set_constraint_handler_s is a null pointer, the
        implementation default handler becomes the current constraint handler.
        Returns

    6   The set_constraint_handler_s function returns a pointer to the previously
        registered handler.[405]

    Footnote 405) If the previous handler was registered by calling set_constraint_handler_s with a null
             pointer argument, a pointer to the implementation default handler is returned (not NULL).

### K.3.6.1.2 [The abort_handler_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdlib.h>
                void abort_handler_s(
                     const char * restrict msg,
                     void * restrict ptr,
                     errno_t error);
        Description

    2   A pointer to the abort_handler_s function shall be a suitable argument to the
        set_constraint_handler_s function.

    3   The abort_handler_s function writes a message on the standard error stream in an
        implementation-defined format. The message shall include the string pointed to by msg.
        The abort_handler_s function then calls the abort function.[406]
        Returns

    Footnote 406) Many implementations invoke a debugger when the abort function is called.

    4   The abort_handler_s function does not return to its caller.

### K.3.6.1.3 [The ignore_handler_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdlib.h>
                 void ignore_handler_s(
                      const char * restrict msg,
                      void * restrict ptr,
                      errno_t error);
        Description

    2   A pointer to the ignore_handler_s function shall be a suitable argument to the
        set_constraint_handler_s function.

    3   The ignore_handler_s function simply returns to its caller.[407]
        Returns

    Footnote 407) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in
             which a runtime-constraint violation occurs will return to its caller. The caller can determine whether
             a runtime-constraint violation occurred based on the library function’s specification (usually, the
             library function returns a nonzero errno_t).

    4   The ignore_handler_s function returns no value.

### K.3.6.2 [Communication with the environment]

### K.3.6.2.1 [The getenv_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdlib.h>
                 errno_t getenv_s(size_t * restrict len,
                            char * restrict value, rsize_t maxsize,
                            const char * restrict name);
        Runtime-constraints

    2   name shall not be a null pointer. maxsize shall neither equal zero nor be greater than
        RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer.

    3   If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len
        is not null), and the environment list is not searched.
        Description

    4   The getenv_s function searches an environment list, provided by the host environment,
        for a string that matches the string pointed to by name.

    5   If that name is found then getenv_s performs the following actions. If len is not a
        null pointer, the length of the string associated with the matched list member is stored in
        the integer pointed to by len. If the length of the associated string is less than maxsize,
        then the associated string is copied to the array pointed to by value.

    6   If that name is not found then getenv_s performs the following actions. If len is not
        a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than
        zero, then value[0] is set to the null character.

    7   The set of environment names and the method for altering the environment list are
        implementation-defined. The getenv_s function need not avoid data races with other
        threads of execution that modify the environment list.[408]
        Returns

    Footnote 408) Many implementations provide non-standard functions that modify the environment list.

    8   The getenv_s function returns zero if the specified name is found and the associated
        string was successfully stored in value. Otherwise, a nonzero value is returned.

### K.3.6.3 [Searching and sorting utilities]

    1   These utilities make use of a comparison function to search or sort arrays of unspecified
        type. Where an argument declared as size_t nmemb specifies the length of the array
        for a function, if nmemb has the value zero on a call to that function, then the comparison
        function is not called, a search finds no matching element, sorting performs no
        rearrangement, and the pointer to the array may be null.

    2   The implementation shall ensure that the second argument of the comparison function
        (when called from bsearch_s), or both arguments (when called from qsort_s), are
        pointers to elements of the array.[409] The first argument when called from bsearch_s
        shall equal key.

    Footnote 409) That is, if the value passed is p, then the following expressions are always valid and nonzero:
                      ((char *)p - (char *)base) % size == 0
                      (char *)p >= (char *)base
                      (char *)p < (char *)base + nmemb * size

    3   The comparison function shall not alter the contents of either the array or search key. The
        implementation may reorder elements of the array between calls to the comparison
        function, but shall not otherwise alter the contents of any individual element.

    4   When the same objects (consisting of size bytes, irrespective of their current positions
        in the array) are passed more than once to the comparison function, the results shall be
        consistent with one another. That is, for qsort_s they shall define a total ordering on
        the array, and for bsearch_s the same object shall always compare the same way with
        the key.

    5   A sequence point occurs immediately before and immediately after each call to the
        comparison function, and also between any call to the comparison function and any
        movement of the objects passed as arguments to that call.

### K.3.6.3.1 [The bsearch_s function]

    1 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <stdlib.h>
                 void *bsearch_s(const void *key, const void *base,
                      rsize_t nmemb, rsize_t size,
                      int (*compar)(const void *k, const void *y,
                                      void *context),
                      void *context);
        Runtime-constraints

    2   Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
        zero, then none of key, base, or compar shall be a null pointer.

    3   If there is a runtime-constraint violation, the bsearch_s function does not search the
        array.
        Description

    4   The bsearch_s function searches an array of nmemb objects, the initial element of
        which is pointed to by base, for an element that matches the object pointed to by key.
        The size of each element of the array is specified by size.

    5   The comparison function pointed to by compar is called with three arguments. The first
        two point to the key object and to an array element, in that order. The function shall
        return an integer less than, equal to, or greater than zero if the key object is considered,
        respectively, to be less than, to match, or to be greater than the array element. The array
        shall consist of: all the elements that compare less than, all the elements that compare
        equal to, and all the elements that compare greater than the key object, in that order.[410]
        The third argument to the comparison function is the context argument passed to
        bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison
        function.[411]
        Returns

    Footnote 410) In practice, this means that the entire array has been sorted according to the comparison function.

    Footnote 411) The context argument is for the use of the comparison function in performing its duties. For
             example, it might specify a collating sequence used by the comparison function.

    6   The bsearch_s function returns a pointer to a matching element of the array, or a null
        pointer if no match is found or there is a runtime-constraint violation. If two elements
        compare as equal, which element is matched is unspecified.

### K.3.6.3.2 [The qsort_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdlib.h>
                errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
                     int (*compar)(const void *x, const void *y,
                                     void *context),
                     void *context);
        Runtime-constraints

    2   Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
        zero, then neither base nor compar shall be a null pointer.

    3   If there is a runtime-constraint violation, the qsort_s function does not sort the array.
        Description

    4   The qsort_s function sorts an array of nmemb objects, the initial element of which is
        pointed to by base. The size of each object is specified by size.

    5   The contents of the array are sorted into ascending order according to a comparison
        function pointed to by compar, which is called with three arguments. The first two
        point to the objects being compared. The function shall return an integer less than, equal
        to, or greater than zero if the first argument is considered to be respectively less than,
        equal to, or greater than the second. The third argument to the comparison function is the
        context argument passed to qsort_s. The sole use of context by qsort_s is to
        pass it to the comparison function.[412]

    Footnote 412) The context argument is for the use of the comparison function in performing its duties. For
             example, it might specify a collating sequence used by the comparison function.

    6   If two elements compare as equal, their relative order in the resulting sorted array is
        unspecified.
        Returns

    7   The qsort_s function returns zero if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

### K.3.6.4 [Multibyte/wide character conversion functions]

    1   The behavior of the multibyte character functions is affected by the LC_CTYPE category
        of the current locale. For a state-dependent encoding, each function is placed into its
        initial conversion state by a call for which its character pointer argument, s, is a null
        pointer. Subsequent calls with s as other than a null pointer cause the internal conversion
        state of the function to be altered as necessary. A call with s as a null pointer causes
        these functions to set the int pointed to by their status argument to a nonzero value if
        encodings have state dependency, and zero otherwise.[413] Changing the LC_CTYPE
        category causes the conversion state of these functions to be indeterminate.

    Footnote 413) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
             character codes, but are grouped with an adjacent multibyte character.

### K.3.6.4.1 [The wctomb_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdlib.h>
                errno_t wctomb_s(int * restrict status,
                     char * restrict s,
                     rsize_t smax,
                     wchar_t wc);
        Runtime-constraints

    2   Let n denote the number of bytes needed to represent the multibyte character
        corresponding to the wide character given by wc (including any shift sequences).

    3   If s is not a null pointer, then smax shall not be less than n, and smax shall not be
        greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero.

    4   If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to
        by status, and if s is not a null pointer, no more than smax elements in the array
        pointed to by s will be accessed.
        Description

    5   The wctomb_s function determines n and stores the multibyte character representation
        of wc in the array whose first element is pointed to by s (if s is not a null pointer). The
        number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide
        character, a null byte is stored, preceded by any shift sequence needed to restore the
        initial shift state, and the function is left in the initial conversion state.

    6   The implementation shall behave as if no library function calls the wctomb_s function.

    7    If s is a null pointer, the wctomb_s function stores into the int pointed to by status a
         nonzero or zero value, if multibyte character encodings, respectively, do or do not have
         state-dependent encodings.

    8    If s is not a null pointer, the wctomb_s function stores into the int pointed to by
         status either n or −1 if wc, respectively, does or does not correspond to a valid
         multibyte character.

    9    In no case will the int pointed to by status be set to a value greater than the
         MB_CUR_MAX macro.
         Returns

    10   The wctomb_s function returns zero if successful, and a nonzero value if there was a
         runtime-constraint violation or wc did not correspond to a valid multibyte character.

### K.3.6.5 [Multibyte/wide string conversion functions]

    1    The behavior of the multibyte string functions is affected by the LC_CTYPE category of
         the current locale.

### K.3.6.5.1 [The mbstowcs_s function]

    1 Synopsis
               #include <stdlib.h>
                errno_t mbstowcs_s(size_t * restrict retval,
                     wchar_t * restrict dst, rsize_t dstmax,
                     const char * restrict src, rsize_t len);
         Runtime-constraints

    2    Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
         neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
         then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
         zero. If dst is not a null pointer and len is not less than dstmax, then a null character
         shall occur within the first dstmax multibyte characters of the array pointed to by src.

    3    If there is a runtime-constraint violation, then mbstowcs_s does the following. If
         retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If
         dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
         then mbstowcs_s sets dst[0] to the null wide character.
         Description

    4    The mbstowcs_s function converts a sequence of multibyte characters that begins in
         the initial shift state from the array pointed to by src into a sequence of corresponding
         wide characters. If dst is not a null pointer, the converted characters are stored into the
         array pointed to by dst. Conversion continues up to and including a terminating null
         character, which is also stored. Conversion stops earlier in two cases: when a sequence of
        bytes is encountered that does not form a valid multibyte character, or (if dst is not a
        null pointer) when len wide characters have been stored into the array pointed to by
        dst.[414] If dst is not a null pointer and no null wide character was stored into the array
        pointed to by dst, then dst[len] is set to the null wide character. Each conversion
        takes place as if by a call to the mbrtowc function.

    Footnote 414) Thus, the value of len is ignored if dst is a null pointer.

    5   Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
        sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
        the mbstowcs_s function stores the value (size_t)(-1) into *retval.
        Otherwise, the mbstowcs_s function stores into *retval the number of multibyte
        characters successfully converted, not including the terminating null character (if any).

    6   All elements following the terminating null wide character (if any) written by
        mbstowcs_s in the array of dstmax wide characters pointed to by dst take
        unspecified values when mbstowcs_s returns.[415]

    Footnote 415) This allows an implementation to attempt converting the multibyte string before discovering a
             terminating null character did not occur where required.

    7   If copying takes place between objects that overlap, the objects take on unspecified
        values.
        Returns

    8   The mbstowcs_s function returns zero if no runtime-constraint violation and no
        encoding error occurred. Otherwise, a nonzero value is returned.

### K.3.6.5.2 [The wcstombs_s function]

    1 Synopsis
                #include <stdlib.h>
                 errno_t wcstombs_s(size_t * restrict retval,
                      char * restrict dst, rsize_t dstmax,
                      const wchar_t * restrict src, rsize_t len);
        Runtime-constraints

    2   Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
        neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
        then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
        zero. If dst is not a null pointer and len is not less than dstmax, then the conversion
        shall have been stopped (see below) because a terminating null wide character was
        reached or because an encoding error occurred.

    3   If there is a runtime-constraint violation, then wcstombs_s does the following. If
        retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If
        dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
        then wcstombs_s sets dst[0] to the null character.
        Description

    4   The wcstombs_s function converts a sequence of wide characters from the array
        pointed to by src into a sequence of corresponding multibyte characters that begins in
        the initial shift state. If dst is not a null pointer, the converted characters are then stored
        into the array pointed to by dst. Conversion continues up to and including a terminating
        null wide character, which is also stored. Conversion stops earlier in two cases:
        — when a wide character is reached that does not correspond to a valid multibyte
          character;
        — (if dst is not a null pointer) when the next multibyte character would exceed the
            limit of n total bytes to be stored into the array pointed to by dst. If the wide
            character being converted is the null wide character, then n is the lesser of len or
            dstmax. Otherwise, n is the lesser of len or dstmax-1.
        If the conversion stops without converting a null wide character and dst is not a null
        pointer, then a null character is stored into the array pointed to by dst immediately
        following any multibyte characters already stored. Each conversion takes place as if by a
        call to the wcrtomb function.[416]

    Footnote 416) If conversion stops because a terminating null wide character has been reached, the bytes stored
             include those necessary to reach the initial shift state immediately before the null byte. However, if
             the conversion stops before a terminating null wide character has been reached, the result will be null
             terminated, but might not end in the initial shift state.

    5   Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
        wide character that does not correspond to a valid multibyte character, an encoding error
        occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval.
        Otherwise, the wcstombs_s function stores into *retval the number of bytes in the
        resulting multibyte character sequence, not including the terminating null character (if
        any).

    6   All elements following the terminating null character (if any) written by wcstombs_s
        in the array of dstmax elements pointed to by dst take unspecified values when
        wcstombs_s returns.[417]

    Footnote 417) When len is not less than dstmax, the implementation might fill the array before discovering a
             runtime-constraint violation.

    7   If copying takes place between objects that overlap, the objects take on unspecified
        values.
        Returns

    8   The wcstombs_s function returns zero if no runtime-constraint violation and no
        encoding error occurred. Otherwise, a nonzero value is returned.

### K.3.7 [String handling <string.h>]

    1   The header <string.h> defines two types.

    2   The types are
               errno_t
        which is type int; and
               rsize_t
        which is the type size_t.

### K.3.7.1 [Copying functions]

### K.3.7.1.1 [The memcpy_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <string.h>
               errno_t memcpy_s(void * restrict s1, rsize_t s1max,
                    const void * restrict s2, rsize_t n);
        Runtime-constraints

    2   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
        RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
        objects that overlap.

    3   If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first
        s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is
        not greater than RSIZE_MAX.
        Description

    4   The memcpy_s function copies n characters from the object pointed to by s2 into the
        object pointed to by s1.
        Returns

    5   The memcpy_s function returns zero if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

### K.3.7.1.2 [The memmove_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <string.h>
               errno_t memmove_s(void *s1, rsize_t s1max,
                    const void *s2, rsize_t n);
        Runtime-constraints

    2   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
        RSIZE_MAX. n shall not be greater than s1max.

    3   If there is a runtime-constraint violation, the memmove_s function stores zeros in the
        first s1max characters of the object pointed to by s1 if s1 is not a null pointer and
        s1max is not greater than RSIZE_MAX.
        Description

    4   The memmove_s function copies n characters from the object pointed to by s2 into the
        object pointed to by s1. This copying takes place as if the n characters from the object
        pointed to by s2 are first copied into a temporary array of n characters that does not
        overlap the objects pointed to by s1 or s2, and then the n characters from the temporary
        array are copied into the object pointed to by s1.
        Returns

    5   The memmove_s function returns zero if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

### K.3.7.1.3 [The strcpy_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <string.h>
               errno_t strcpy_s(char * restrict s1,
                    rsize_t s1max,
                    const char * restrict s2);
        Runtime-constraints

    2   Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
        s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max).
        Copying shall not take place between objects that overlap.

    3   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
        greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the
        null character.
        Description

    4   The strcpy_s function copies the string pointed to by s2 (including the terminating
        null character) into the array pointed to by s1.

    5   All elements following the terminating null character (if any) written by strcpy_s in
        the array of s1max characters pointed to by s1 take unspecified values when
        strcpy_s returns.[418]
        Returns

    Footnote 418) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
             any of those characters are null. Such an approach might write a character to every element of s1
             before discovering that the first element should be set to the null character.

    6   The strcpy_s function returns zero[419] if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

    Footnote 419) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
             within the array pointed to by s1 and that the result in s1 is null terminated.

### K.3.7.1.4 [The strncpy_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                errno_t strncpy_s(char * restrict s1,
                     rsize_t s1max,
                     const char * restrict s2,
                     rsize_t n);
        Runtime-constraints

    2   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
        RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
        shall be greater than strnlen_s(s2, s1max). Copying shall not take place between
        objects that overlap.

    3   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
        greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the
        null character.
        Description

    4   The strncpy_s function copies not more than n successive characters (characters that
        follow a null character are not copied) from the array pointed to by s2 to the array
        pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null
        character.

    5   All elements following the terminating null character (if any) written by strncpy_s in
        the array of s1max characters pointed to by s1 take unspecified values when
        strncpy_s returns.[420]
        Returns

    Footnote 420) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
             any of those characters are null. Such an approach might write a character to every element of s1
             before discovering that the first element should be set to the null character.

    6   The strncpy_s function returns zero[421] if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

    Footnote 421) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
             within the array pointed to by s1 and that the result in s1 is null terminated.

    7   EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result
        will not be null terminated or that characters will be written past the end of the destination array.
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                /* ... */
                char src1[100] = "hello";
                char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'};
                char dst1[6], dst2[5], dst3[5];
                int r1, r2, r3;
                r1 = strncpy_s(dst1, 6, src1, 100);
                r2 = strncpy_s(dst2, 5, src2, 7);
                r3 = strncpy_s(dst3, 5, src2, 4);
        The first call will assign to r1 the value zero and to dst1 the sequence hello\0.
        The second call will assign to r2 a nonzero value and to dst2 the sequence \0.
        The third call will assign to r3 the value zero and to dst3 the sequence good\0.

### K.3.7.2 [Concatenation functions]

### K.3.7.2.1 [The strcat_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                errno_t strcat_s(char * restrict s1,
                     rsize_t s1max,
                     const char * restrict s2);
        Runtime-constraints

    2   Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
        strcat_s.

    3   Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
        s1max shall not equal zero. m shall not equal zero.[422] m shall be greater than
        strnlen_s(s2, m). Copying shall not take place between objects that overlap.

    Footnote 422) Zero means that s1 was not null terminated upon entry to strcat_s.

    4   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
        greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the
        null character.
        Description

    5   The strcat_s function appends a copy of the string pointed to by s2 (including the
        terminating null character) to the end of the string pointed to by s1. The initial character
        from s2 overwrites the null character at the end of s1.

    6   All elements following the terminating null character (if any) written by strcat_s in
        the array of s1max characters pointed to by s1 take unspecified values when
        strcat_s returns.[423]
        Returns

    Footnote 423) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
             any of those characters are null. Such an approach might write a character to every element of s1
             before discovering that the first element should be set to the null character.

    7   The strcat_s function returns zero[424] if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

    Footnote 424) A zero return value implies that all of the requested characters from the string pointed to by s2 were
             appended to the string pointed to by s1 and that the result in s1 is null terminated.

### K.3.7.2.2 [The strncat_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                errno_t strncat_s(char * restrict s1,
                     rsize_t s1max,
                     const char * restrict s2,
                     rsize_t n);
        Runtime-constraints

    2   Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
        strncat_s.

    3   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
        RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.[425] If n is not less
        than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take
        place between objects that overlap.

    Footnote 425) Zero means that s1 was not null terminated upon entry to strncat_s.

    4   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
        greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the
        null character.
        Description

    5   The strncat_s function appends not more than n successive characters (characters
        that follow a null character are not copied) from the array pointed to by s2 to the end of
        the string pointed to by s1. The initial character from s2 overwrites the null character at
        the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to
        a null character.

    6   All elements following the terminating null character (if any) written by strncat_s in
        the array of s1max characters pointed to by s1 take unspecified values when
        strncat_s returns.[426]
        Returns

    Footnote 426) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
             any of those characters are null. Such an approach might write a character to every element of s1
             before discovering that the first element should be set to the null character.

    7   The strncat_s function returns zero[427] if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

    Footnote 427) A zero return value implies that all of the requested characters from the string pointed to by s2 were
             appended to the string pointed to by s1 and that the result in s1 is null terminated.

    8   EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result
        will not be null terminated or that characters will be written past the end of the destination array.
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                /* ... */
                char s1[100] = "good";
                char s2[6] = "hello";
                char s3[6] = "hello";
                char s4[7] = "abc";
                char s5[1000] = "bye";
                int r1, r2, r3, r4;
                r1 = strncat_s(s1, 100, s5, 1000);
                r2 = strncat_s(s2, 6, "", 1);
                r3 = strncat_s(s3, 6, "X", 2);
                r4 = strncat_s(s4, 7, "defghijklmn", 3);
        After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0.
        After the second call r2 will have the value zero and s2 will contain the sequence hello\0.
        After the third call r3 will have a nonzero value and s3 will contain the sequence \0.
        After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0.

### K.3.7.3 [Search functions]

### K.3.7.3.1 [The strtok_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                char *strtok_s(char * restrict s1,
                     rsize_t * restrict s1max,
                     const char * restrict s2,
                     char ** restrict ptr);
        Runtime-constraints

    2   None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
        shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
        The end of the token found shall occur within the first *s1max characters of s1 for the
        first call, and shall occur within the first *s1max characters of where searching resumes
        on subsequent calls.

    3   If there is a runtime-constraint violation, the strtok_s function does not indirect
        through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
        Description

    4   A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a
        sequence of tokens, each of which is delimited by a character from the string pointed to
        by s2. The fourth argument points to a caller-provided char pointer into which the
        strtok_s function stores information necessary for it to continue scanning the same
        string.

    5   The first call in a sequence has a non-null first argument and s1max points to an object
        whose value is the number of elements in the character array pointed to by the first
        argument. The first call stores an initial value in the object pointed to by ptr and
        updates the value pointed to by s1max to reflect the number of elements that remain in
        relation to ptr. Subsequent calls in the sequence have a null first argument and the
        objects pointed to by s1max and ptr are required to have the values stored by the
        previous call in the sequence, which are then updated. The separator string pointed to by
        s2 may be different from call to call.

    6   The first call in the sequence searches the string pointed to by s1 for the first character
        that is not contained in the current separator string pointed to by s2. If no such character
        is found, then there are no tokens in the string pointed to by s1 and the strtok_s
        function returns a null pointer. If such a character is found, it is the start of the first token.

    7    The strtok_s function then searches from there for the first character in s1 that is
         contained in the current separator string. If no such character is found, the current token
         extends to the end of the string pointed to by s1, and subsequent searches in the same
         string for a token return a null pointer. If such a character is found, it is overwritten by a
         null character, which terminates the current token.

    8    In all cases, the strtok_s function stores sufficient information in the pointer pointed
         to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
         value for ptr, shall start searching just past the element overwritten by a null character
         (if any).
         Returns

    9    The strtok_s function returns a pointer to the first character of a token, or a null
         pointer if there is no token or there is a runtime-constraint violation.

    10   EXAMPLE
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                static char str1[] = "?a???b,,,#c";
                static char str2[] = "\t \t";
                char *t, *ptr1, *ptr2;
                rsize_t max1 = sizeof (str1);
                rsize_t max2 = sizeof (str2);
                t = strtok_s(str1, &max1, "?", &ptr1);                 // t points to the token "a"
                t = strtok_s(NULL, &max1, ",", &ptr1);                 // t points to the token "??b"
                t = strtok_s(str2, &max2, " \t", &ptr2);               // t is a null pointer
                t = strtok_s(NULL, &max1, "#,", &ptr1);                // t points to the token "c"
                t = strtok_s(NULL, &max1, "?", &ptr1);                 // t is a null pointer

### K.3.7.4 [Miscellaneous functions]

### K.3.7.4.1 [The memset_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
         Runtime-constraints

    2    s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n
         shall not be greater than smax.

    3    If there is a runtime-constraint violation, then if s is not a null pointer and smax is not
         greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an
         unsigned char) into each of the first smax characters of the object pointed to by s.
        Description

    4   The memset_s function copies the value of c (converted to an unsigned char) into
        each of the first n characters of the object pointed to by s. Unlike memset, any call to
        the memset_s function shall be evaluated strictly according to the rules of the abstract
        machine as described in (5.1.2.3). That is, any call to the memset_s function shall
        assume that the memory indicated by s and n may be accessible in the future and thus
        must contain the values indicated by c.
        Returns

    5   The memset_s function returns zero if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

### K.3.7.4.2 [The strerror_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <string.h>
               errno_t strerror_s(char *s, rsize_t maxsize,
                    errno_t errnum);
        Runtime-constraints

    2   s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX.
        maxsize shall not equal zero.

    3   If there is a runtime-constraint violation, then the array (if any) pointed to by s is not
        modified.
        Description

    4   The strerror_s function maps the number in errnum to a locale-specific message
        string. Typically, the values for errnum come from errno, but strerror_s shall
        map any value of type int to a message.

    5   If the length of the desired string is less than maxsize, then the string is copied to the
        array pointed to by s.

    6   Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied
        from the string to the array pointed to by s and then s[maxsize-1] is set to the null
        character. Then, if maxsize is greater than 3, then s[maxsize-2],
        s[maxsize-3], and s[maxsize-4] are set to the character period (.).
        Returns

    7   The strerror_s function returns zero if the length of the desired string was less than
        maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s
        function returns a nonzero value.

### K.3.7.4.3 [The strerrorlen_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                size_t strerrorlen_s(errno_t errnum);
        Description

    2   The strerrorlen_s function calculates the length of the (untruncated) locale-specific
        message string that the strerror_s function maps to errnum.
        Returns

    3   The strerrorlen_s function returns the number of characters (not including the null
        character) in the full message string.

### K.3.7.4.4 [The strnlen_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <string.h>
                size_t strnlen_s(const char *s, size_t maxsize);
        Description

    2   The strnlen_s function computes the length of the string pointed to by s.
        Returns

    3   If s is a null pointer,[428] then the strnlen_s function returns zero.

    Footnote 428) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints
             along with the values returned for a null pointer or an unterminated string argument make
             strnlen_s useful in algorithms that gracefully handle such exceptional data.

    4   Otherwise, the strnlen_s function returns the number of characters that precede the
        terminating null character. If there is no null character in the first maxsize characters of
        s then strnlen_s returns maxsize. At most the first maxsize characters of s shall
        be accessed by strnlen_s.

### K.3.8 [Date and time <time.h>]

    1   The header <time.h> defines two types.

    2   The types are
                errno_t
        which is type int; and
                rsize_t
        which is the type size_t.

### K.3.8.1 [Components of time]

    1   A broken-down time is normalized if the values of the members of the tm structure are in
        their normal rages.[429]

    Footnote 429) The normal ranges are defined in 7.27.1.

### K.3.8.2 [Time conversion functions]

    1   Like the strftime function, the asctime_s and ctime_s functions do not return a
        pointer to a static object, and other library functions are permitted to call them.

### K.3.8.2.1 [The asctime_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <time.h>
                errno_t asctime_s(char *s, rsize_t maxsize,
                     const struct tm *timeptr);
        Runtime-constraints

    2   Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and
        shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr
        shall be normalized. The calendar year represented by the broken-down time pointed to
        by timeptr shall not be less than calendar year 0 and shall not be greater than calendar
        year 9999.

    3   If there is a runtime-constraint violation, there is no attempt to convert the time, and
        s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is
        not greater than RSIZE_MAX.
        Description

    4   The asctime_s function converts the normalized broken-down time in the structure
        pointed to by timeptr into a 26 character (including the null character) string in the
        form
                Sun Sep 16 01:03:52 1973\n\0
        The fields making up this string are (in order):
           1.   The name of the day of the week represented by timeptr->tm_wday using the
                following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat.
           2.   The character space.
           3. The name of the month represented by timeptr->tm_mon using the following
              three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct,
              Nov, and Dec.
           4.   The character space.
           5.   The value of timeptr->tm_mday as if printed using the fprintf format
                "%2d".
           6.   The character space.
           7.   The value of timeptr->tm_hour as if printed using the fprintf format
                "%.2d".
           8.   The character colon.
           9.   The value of timeptr->tm_min as if printed using the fprintf format
                "%.2d".
         10.    The character colon.
         11.    The value of timeptr->tm_sec as if printed using the fprintf format
                "%.2d".
         12.    The character space.
         13.    The value of timeptr->tm_year + 1900 as if printed using the fprintf
                format "%4d".
         14.    The character new line.
         15.    The null character.
        Recommended practice
        The strftime function allows more flexible formatting and supports locale-specific
        behavior. If you do not require the exact form of the result string produced by the
        asctime_s function, consider using the strftime function instead.
        Returns

    5   The asctime_s function returns zero if the time was successfully converted and stored
        into the array pointed to by s. Otherwise, it returns a nonzero value.

### K.3.8.2.2 [The ctime_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <time.h>
               errno_t ctime_s(char *s, rsize_t maxsize,
                    const time_t *timer);
        Runtime-constraints

    2   Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and
        shall not be greater than RSIZE_MAX.

    3   If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null
        pointer and maxsize is not equal zero and is not greater than RSIZE_MAX.
        Description

    4   The ctime_s function converts the calendar time pointed to by timer to local time in
        the form of a string. It is equivalent to
               asctime_s(s, maxsize, localtime_s(timer))
        Recommended practice
        The strftime function allows more flexible formatting and supports locale-specific
        behavior. If you do not require the exact form of the result string produced by the
        ctime_s function, consider using the strftime function instead.
        Returns

    5   The ctime_s function returns zero if the time was successfully converted and stored
        into the array pointed to by s. Otherwise, it returns a nonzero value.

### K.3.8.2.3 [The gmtime_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <time.h>
               struct tm *gmtime_s(const time_t * restrict timer,
                    struct tm * restrict result);
        Runtime-constraints

    2   Neither timer nor result shall be a null pointer.

    3   If there is a runtime-constraint violation, there is no attempt to convert the time.
        Description

    4   The gmtime_s function converts the calendar time pointed to by timer into a broken-
        down time, expressed as UTC. The broken-down time is stored in the structure pointed
        to by result.
        Returns

    5   The gmtime_s function returns result, or a null pointer if the specified time cannot
        be converted to UTC or there is a runtime-constraint violation.

### K.3.8.2.4 [The localtime_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <time.h>
               struct tm *localtime_s(const time_t * restrict timer,
                    struct tm * restrict result);
        Runtime-constraints

    2   Neither timer nor result shall be a null pointer.

    3   If there is a runtime-constraint violation, there is no attempt to convert the time.
        Description

    4   The localtime_s function converts the calendar time pointed to by timer into a
        broken-down time, expressed as local time. The broken-down time is stored in the
        structure pointed to by result.
        Returns

    5   The localtime_s function returns result, or a null pointer if the specified time
        cannot be converted to local time or there is a runtime-constraint violation.

### K.3.9 [Extended multibyte and wide character utilities <wchar.h>]

    1   The header <wchar.h> defines two types.

    2   The types are
               errno_t
        which is type int; and
               rsize_t
        which is the type size_t.

    3   Unless explicitly stated otherwise, if the execution of a function described in this
        subclause causes copying to take place between objects that overlap, the objects take on
        unspecified values.

### K.3.9.1 [Formatted wide character input/output functions]

### K.3.9.1.1 [The fwprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                int fwprintf_s(FILE * restrict stream,
                     const wchar_t * restrict format, ...);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. The %n specifier[430] (modified or
        not by flags, field width, or precision) shall not appear in the wide string pointed to by
        format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a
        null pointer.

    Footnote 430) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, the fwprintf_s function does not attempt to
        produce further output, and it is unspecified to what extent fwprintf_s produced
        output before discovering the runtime-constraint violation.
        Description

    4   The fwprintf_s function is equivalent to the fwprintf function except for the
        explicit runtime-constraints listed above.
        Returns

    5   The fwprintf_s function returns the number of wide characters transmitted, or a
        negative value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.9.1.2 [The fwscanf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdio.h>
                #include <wchar.h>
                int fwscanf_s(FILE * restrict stream,
                     const wchar_t * restrict format, ...);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. Any argument indirected though in
        order to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the fwscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent fwscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The fwscanf_s function is equivalent to fwscanf except that the c, s, and [
        conversion specifiers apply to a pair of arguments (unless assignment suppression is
        indicated by a *). The first of these arguments is the same as for fwscanf. That
        argument is immediately followed in the argument list by the second argument, which has
        type size_t and gives the number of elements in the array pointed to by the first
        argument of the pair. If the first argument points to a scalar object, it is considered to be
        an array of one element.[431]

    Footnote 431) If the format is known at translation time, an implementation may issue a diagnostic for any argument
             used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
             argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
             the format is not known at translation time. For example, an implementation may issue a diagnostic
             for each argument after format that has of type pointer to one of char, signed char,
             unsigned char, or void that is not followed by an argument of a type compatible with
             rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
             using the hh length modifier, a length argument must follow the pointer argument. Another useful
             diagnostic could flag any non-pointer argument following format that did not have a type
             compatible with rsize_t.

    5   A matching failure occurs if the number of elements in a receiving object is insufficient to
        hold the converted input (including any trailing null character).
        Returns

    6   The fwscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        fwscanf_s function returns the number of input items assigned, which can be fewer
        than provided for, or even zero, in the event of an early matching failure.

### K.3.9.1.3 [The snwprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                int snwprintf_s(wchar_t * restrict s,
                     rsize_t n,
                     const wchar_t * restrict format, ...);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The %n specifier[432] (modified or not by flags, field width, or
        precision) shall not appear in the wide string pointed to by format. Any argument to
        snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
        error shall occur.

    Footnote 432) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the
        null wide character.
        Description

    4   The snwprintf_s function is equivalent to the swprintf function except for the
        explicit runtime-constraints listed above.

    5   The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within
        the array pointed to by s.
        Returns

    6   The snwprintf_s function returns the number of wide characters that would have
        been written had n been sufficiently large, not counting the terminating wide null
        character, or a negative value if a runtime-constraint violation occurred. Thus, the null-
        terminated output has been completely written if and only if the returned value is
        nonnegative and less than n.

### K.3.9.1.4 [The swprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                int swprintf_s(wchar_t * restrict s, rsize_t n,
                     const wchar_t * restrict format, ...);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The number of wide characters (including the trailing null) required
        for the result to be written to the array pointed to by s shall not be greater than n. The %n
        specifier[433] (modified or not by flags, field width, or precision) shall not appear in the
        wide string pointed to by format. Any argument to swprintf_s corresponding to a
        %s specifier shall not be a null pointer. No encoding error shall occur.

    Footnote 433) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the
        null wide character.
        Description

    4   The swprintf_s function is equivalent to the swprintf function except for the
        explicit runtime-constraints listed above.

    5   The swprintf_s function, unlike snwprintf_s, treats a result too big for the array
        pointed to by s as a runtime-constraint violation.
        Returns

    6   If no runtime-constraint violation occurred, the swprintf_s function returns the
        number of wide characters written in the array, not counting the terminating null wide
        character. If an encoding error occurred or if n or more wide characters are requested to
        be written, swprintf_s returns a negative value. If any other runtime-constraint
        violation occurred, swprintf_s returns zero.

### K.3.9.1.5 [The swscanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <wchar.h>
               int swscanf_s(const wchar_t * restrict s,
                    const wchar_t * restrict format, ...);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. Any argument indirected though in order
        to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the swscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent swscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The swscanf_s function is equivalent to fwscanf_s, except that the argument s
        specifies a wide string from which the input is to be obtained, rather than from a stream.
        Reaching the end of the wide string is equivalent to encountering end-of-file for the
        fwscanf_s function.
        Returns

    5   The swscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        swscanf_s function returns the number of input items assigned, which can be fewer
        than provided for, or even zero, in the event of an early matching failure.

### K.3.9.1.6 [The vfwprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdarg.h>
                #include <stdio.h>
                #include <wchar.h>
                int vfwprintf_s(FILE * restrict stream,
                     const wchar_t * restrict format,
                     va_list arg);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. The %n specifier[434] (modified or
        not by flags, field width, or precision) shall not appear in the wide string pointed to by
        format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be
        a null pointer.

    Footnote 434) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, the vfwprintf_s function does not attempt
        to produce further output, and it is unspecified to what extent vfwprintf_s produced
        output before discovering the runtime-constraint violation.
        Description

    4   The vfwprintf_s function is equivalent to the vfwprintf function except for the
        explicit runtime-constraints listed above.
        Returns

    5   The vfwprintf_s function returns the number of wide characters transmitted, or a
        negative value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.9.1.7 [The vfwscanf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdarg.h>
                #include <stdio.h>
                #include <wchar.h>
                int vfwscanf_s(FILE * restrict stream,
                     const wchar_t * restrict format, va_list arg);
        Runtime-constraints

    2   Neither stream nor format shall be a null pointer. Any argument indirected though in
        order to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent vfwscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument
        list replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the
        va_end macro.[435]
        Returns

    Footnote 435) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
             value of arg after the return is indeterminate.

    5   The vfwscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        vfwscanf_s function returns the number of input items assigned, which can be fewer
        than provided for, or even zero, in the event of an early matching failure.

### K.3.9.1.8 [The vsnwprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdarg.h>
                #include <wchar.h>
                int vsnwprintf_s(wchar_t * restrict s,
                     rsize_t n,
                     const wchar_t * restrict format,
                     va_list arg);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The %n specifier[436] (modified or not by flags, field width, or
        precision) shall not appear in the wide string pointed to by format. Any argument to
        vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No
        encoding error shall occur.

    Footnote 436) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to
        the null wide character.
        Description

    4   The vsnwprintf_s function is equivalent to the vswprintf function except for the
        explicit runtime-constraints listed above.

    5   The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit
        within the array pointed to by s.
        Returns

    6   The vsnwprintf_s function returns the number of wide characters that would have
        been written had n been sufficiently large, not counting the terminating null character, or
        a negative value if a runtime-constraint violation occurred. Thus, the null-terminated
        output has been completely written if and only if the returned value is nonnegative and
        less than n.

### K.3.9.1.9 [The vswprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdarg.h>
                #include <wchar.h>
                int vswprintf_s(wchar_t * restrict s,
                     rsize_t n,
                     const wchar_t * restrict format,
                     va_list arg);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
        than RSIZE_MAX. The number of wide characters (including the trailing null) required
        for the result to be written to the array pointed to by s shall not be greater than n. The %n
        specifier[437] (modified or not by flags, field width, or precision) shall not appear in the
        wide string pointed to by format. Any argument to vswprintf_s corresponding to a
        %s specifier shall not be a null pointer. No encoding error shall occur.

    Footnote 437) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
        than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the
        null wide character.
        Description

    4   The vswprintf_s function is equivalent to the vswprintf function except for the
        explicit runtime-constraints listed above.

    5   The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the
        array pointed to by s as a runtime-constraint violation.
        Returns

    6   If no runtime-constraint violation occurred, the vswprintf_s function returns the
        number of wide characters written in the array, not counting the terminating null wide
        character. If an encoding error occurred or if n or more wide characters are requested to
        be written, vswprintf_s returns a negative value. If any other runtime-constraint
        violation occurred, vswprintf_s returns zero.

### K.3.9.1.10 [The vswscanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <stdarg.h>
               #include <wchar.h>
               int vswscanf_s(const wchar_t * restrict s,
                    const wchar_t * restrict format,
                    va_list arg);
        Runtime-constraints

    2   Neither s nor format shall be a null pointer. Any argument indirected though in order
        to store converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the vswscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent vswscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The vswscanf_s function is equivalent to swscanf_s, with the variable argument
        list replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vswscanf_s function does not invoke the
        va_end macro.[438]
        Returns

    Footnote 438) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
             value of arg after the return is indeterminate.

    5   The vswscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        vswscanf_s function returns the number of input items assigned, which can be fewer
        than provided for, or even zero, in the event of an early matching failure.

### K.3.9.1.11 [The vwprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdarg.h>
                #include <wchar.h>
                int vwprintf_s(const wchar_t * restrict format,
                     va_list arg);
        Runtime-constraints

    2   format shall not be a null pointer. The %n specifier[439] (modified or not by flags, field
        width, or precision) shall not appear in the wide string pointed to by format. Any
        argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer.

    Footnote 439) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, the vwprintf_s function does not attempt to
        produce further output, and it is unspecified to what extent vwprintf_s produced
        output before discovering the runtime-constraint violation.
        Description

    4   The vwprintf_s function is equivalent to the vwprintf function except for the
        explicit runtime-constraints listed above.
        Returns

    5   The vwprintf_s function returns the number of wide characters transmitted, or a
        negative value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.9.1.12 [The vwscanf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <stdarg.h>
                #include <wchar.h>
                int vwscanf_s(const wchar_t * restrict format,
                     va_list arg);
        Runtime-constraints

    2   format shall not be a null pointer. Any argument indirected though in order to store
        converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the vwscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent vwscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The vwscanf_s function is equivalent to wscanf_s, with the variable argument list
        replaced by arg, which shall have been initialized by the va_start macro (and
        possibly subsequent va_arg calls). The vwscanf_s function does not invoke the
        va_end macro.[440]
        Returns

    Footnote 440) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
             value of arg after the return is indeterminate.

    5   The vwscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        vwscanf_s function returns the number of input items assigned, which can be fewer
        than provided for, or even zero, in the event of an early matching failure.

### K.3.9.1.13 [The wprintf_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                int wprintf_s(const wchar_t * restrict format, ...);
        Runtime-constraints

    2   format shall not be a null pointer. The %n specifier[441] (modified or not by flags, field
        width, or precision) shall not appear in the wide string pointed to by format. Any
        argument to wprintf_s corresponding to a %s specifier shall not be a null pointer.

    Footnote 441) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
             string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
             example, if the entire format string was L"%%n".

    3   If there is a runtime-constraint violation, the wprintf_s function does not attempt to
        produce further output, and it is unspecified to what extent wprintf_s produced output
        before discovering the runtime-constraint violation.
        Description

    4   The wprintf_s function is equivalent to the wprintf function except for the explicit
        runtime-constraints listed above.
        Returns

    5   The wprintf_s function returns the number of wide characters transmitted, or a
        negative value if an output error, encoding error, or runtime-constraint violation occurred.

### K.3.9.1.14 [The wscanf_s function]

    1 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
               #include <wchar.h>
               int wscanf_s(const wchar_t * restrict format, ...);
        Runtime-constraints

    2   format shall not be a null pointer. Any argument indirected though in order to store
        converted input shall not be a null pointer.

    3   If there is a runtime-constraint violation, the wscanf_s function does not attempt to
        perform further input, and it is unspecified to what extent wscanf_s performed input
        before discovering the runtime-constraint violation.
        Description

    4   The wscanf_s function is equivalent to fwscanf_s with the argument stdin
        interposed before the arguments to wscanf_s.
        Returns

    5   The wscanf_s function returns the value of the macro EOF if an input failure occurs
        before any conversion or if there is a runtime-constraint violation. Otherwise, the
        wscanf_s function returns the number of input items assigned, which can be fewer than
        provided for, or even zero, in the event of an early matching failure.

### K.3.9.2 [General wide string utilities]

### K.3.9.2.1 [Wide string copying functions]

### K.3.9.2.1.1 [The wcscpy_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                errno_t wcscpy_s(wchar_t * restrict s1,
                     rsize_t s1max,
                     const wchar_t * restrict s2);
        Runtime-constraints

    2   Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
        s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max).
        Copying shall not take place between objects that overlap.

    3   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
        greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the
        null wide character.
        Description

    4   The wcscpy_s function copies the wide string pointed to by s2 (including the
        terminating null wide character) into the array pointed to by s1.

    5   All elements following the terminating null wide character (if any) written by
        wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified
        values when wcscpy_s returns.[442]
        Returns

    Footnote 442) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
             if any of those wide characters are null. Such an approach might write a wide character to every
             element of s1 before discovering that the first element should be set to the null wide character.

    6   The wcscpy_s function returns zero[443] if there was no runtime-constraint violation.
        Otherwise, a nonzero value is returned.

    Footnote 443) A zero return value implies that all of the requested wide characters from the string pointed to by s2
             fit within the array pointed to by s1 and that the result in s1 is null terminated.

### K.3.9.2.1.2 [The wcsncpy_s function]

    7 Synopsis
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <wchar.h>
                 errno_t wcsncpy_s(wchar_t * restrict s1,
                      rsize_t s1max,
                      const wchar_t * restrict s2,
                      rsize_t n);
         Runtime-constraints

    8    Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
         RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
         shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between
         objects that overlap.

    9    If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
         greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the
         null wide character.
         Description

    10   The wcsncpy_s function copies not more than n successive wide characters (wide
         characters that follow a null wide character are not copied) from the array pointed to by
         s2 to the array pointed to by s1. If no null wide character was copied from s2, then
         s1[n] is set to a null wide character.

    11   All elements following the terminating null wide character (if any) written by
         wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified
         values when wcsncpy_s returns.[444]
         Returns

    Footnote 444) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
              if any of those wide characters are null. Such an approach might write a wide character to every
              element of s1 before discovering that the first element should be set to the null wide character.

    12   The wcsncpy_s function returns zero[445] if there was no runtime-constraint violation.
         Otherwise, a nonzero value is returned.

    Footnote 445) A zero return value implies that all of the requested wide characters from the string pointed to by s2
              fit within the array pointed to by s1 and that the result in s1 is null terminated.

    13   EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the
         result will not be null terminated or that wide characters will be written past the end of the destination
         array.
                 #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <wchar.h>
                 /* ... */
                 wchar_t src1[100] = L"hello";
                 wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'};
                 wchar_t dst1[6], dst2[5], dst3[5];
                 int r1, r2, r3;
                 r1 = wcsncpy_s(dst1, 6, src1, 100);
                 r2 = wcsncpy_s(dst2, 5, src2, 7);
                 r3 = wcsncpy_s(dst3, 5, src2, 4);
         The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0.
         The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0.
         The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0.

### K.3.9.2.1.3 [The wmemcpy_s function]

    14 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                 #include <wchar.h>
                 errno_t wmemcpy_s(wchar_t * restrict s1,
                      rsize_t s1max,
                      const wchar_t * restrict s2,
                      rsize_t n);
         Runtime-constraints

    15   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
         RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
         objects that overlap.

    16   If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the
         first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
         s1max is not greater than RSIZE_MAX.
         Description

    17   The wmemcpy_s function copies n successive wide characters from the object pointed
         to by s2 into the object pointed to by s1.
         Returns

    18   The wmemcpy_s function returns zero if there was no runtime-constraint violation.
         Otherwise, a nonzero value is returned.

### K.3.9.2.1.4 [The wmemmove_s function]

    19 Synopsis
              #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
                     const wchar_t *s2, rsize_t n);
         Runtime-constraints

    20   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
         RSIZE_MAX. n shall not be greater than s1max.

    21   If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the
         first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
         s1max is not greater than RSIZE_MAX.
         Description

    22   The wmemmove_s function copies n successive wide characters from the object pointed
         to by s2 into the object pointed to by s1. This copying takes place as if the n wide
         characters from the object pointed to by s2 are first copied into a temporary array of n
         wide characters that does not overlap the objects pointed to by s1 or s2, and then the n
         wide characters from the temporary array are copied into the object pointed to by s1.
         Returns

    23   The wmemmove_s function returns zero if there was no runtime-constraint violation.
         Otherwise, a nonzero value is returned.

### K.3.9.2.2 [Wide string concatenation functions]

### K.3.9.2.2.1 [The wcscat_s function]

    1 Synopsis
               #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                errno_t wcscat_s(wchar_t * restrict s1,
                     rsize_t s1max,
                     const wchar_t * restrict s2);
         Runtime-constraints

    2    Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
         wcscat_s.

    3    Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
         s1max shall not equal zero. m shall not equal zero.[446] m shall be greater than
         wcsnlen_s(s2, m). Copying shall not take place between objects that overlap.

    Footnote 446) Zero means that s1 was not null terminated upon entry to wcscat_s.

    4    If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
         greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the
         null wide character.
         Description

    5    The wcscat_s function appends a copy of the wide string pointed to by s2 (including
         the terminating null wide character) to the end of the wide string pointed to by s1. The
         initial wide character from s2 overwrites the null wide character at the end of s1.

    6    All elements following the terminating null wide character (if any) written by
         wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified
         values when wcscat_s returns.[447]
         Returns

    Footnote 447) This allows an implementation to append wide characters from s2 to s1 while simultaneously
              checking if any of those wide characters are null. Such an approach might write a wide character to
              every element of s1 before discovering that the first element should be set to the null wide character.

    7    The wcscat_s function returns zero[448] if there was no runtime-constraint violation.
         Otherwise, a nonzero value is returned.

    Footnote 448) A zero return value implies that all of the requested wide characters from the wide string pointed to by
              s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.

### K.3.9.2.2.2 [The wcsncat_s function]

    8 Synopsis
                 #define _ _STDC_WANT_LIB_EXT1_ _ 1
                  #include <wchar.h>
                  errno_t wcsncat_s(wchar_t * restrict s1,
                       rsize_t s1max,
                       const wchar_t * restrict s2,
                       rsize_t n);
         Runtime-constraints

    9    Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
         wcsncat_s.

    10   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
         RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.[449] If n is not less
         than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take
         place between objects that overlap.

    Footnote 449) Zero means that s1 was not null terminated upon entry to wcsncat_s.

    11   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
         greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the
         null wide character.
         Description

    12   The wcsncat_s function appends not more than n successive wide characters (wide
         characters that follow a null wide character are not copied) from the array pointed to by
         s2 to the end of the wide string pointed to by s1. The initial wide character from s2
         overwrites the null wide character at the end of s1. If no null wide character was copied
         from s2, then s1[s1max-m+n] is set to a null wide character.

    13   All elements following the terminating null wide character (if any) written by
         wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified
         values when wcsncat_s returns.[450]
         Returns

    Footnote 450) This allows an implementation to append wide characters from s2 to s1 while simultaneously
              checking if any of those wide characters are null. Such an approach might write a wide character to
              every element of s1 before discovering that the first element should be set to the null wide character.

    14   The wcsncat_s function returns zero[451] if there was no runtime-constraint violation.
         Otherwise, a nonzero value is returned.

    Footnote 451) A zero return value implies that all of the requested wide characters from the wide string pointed to by
              s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.

    15   EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the
         result will not be null terminated or that wide characters will be written past the end of the destination
         array.
                  #define _ _STDC_WANT_LIB_EXT1_ _ 1
                  #include <wchar.h>
                  /* ... */
                  wchar_t s1[100] = L"good";
                  wchar_t s2[6] = L"hello";
                  wchar_t s3[6] = L"hello";
                  wchar_t s4[7] = L"abc";
                  wchar_t s5[1000] = L"bye";
                  int r1, r2, r3, r4;
                  r1 = wcsncat_s(s1, 100, s5, 1000);
                  r2 = wcsncat_s(s2, 6, L"", 1);
                  r3 = wcsncat_s(s3, 6, L"X", 2);
                  r4 = wcsncat_s(s4, 7, L"defghijklmn", 3);
         After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0.
         After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0.
         After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0.
         After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0.

### K.3.9.2.3 [Wide string search functions]

### K.3.9.2.3.1 [The wcstok_s function]

    1           #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
         Description

    2    The wcsnlen_s function computes the length of the wide string pointed to by s.
         Returns

    3    If s is a null pointer,[452] then the wcsnlen_s function returns zero.

    Footnote 452) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints
             along with the values returned for a null pointer or an unterminated wide string argument make
             wcsnlen_s useful in algorithms that gracefully handle such exceptional data.

    4    Otherwise, the wcsnlen_s function returns the number of wide characters that precede
         the terminating null wide character. If there is no null wide character in the first
         maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first
        maxsize wide characters of s shall be accessed by wcsnlen_s.

    5   The first call in a sequence has a non-null first argument and s1max points to an object
        whose value is the number of elements in the wide character array pointed to by the first
        argument. The first call stores an initial value in the object pointed to by ptr and
        updates the value pointed to by s1max to reflect the number of elements that remain in
        relation to ptr. Subsequent calls in the sequence have a null first argument and the
        objects pointed to by s1max and ptr are required to have the values stored by the
        previous call in the sequence, which are then updated. The separator wide string pointed
        to by s2 may be different from call to call.

    6   The first call in the sequence searches the wide string pointed to by s1 for the first wide
        character that is not contained in the current separator wide string pointed to by s2. If no
        such wide character is found, then there are no tokens in the wide string pointed to by s1
        and the wcstok_s function returns a null pointer. If such a wide character is found, it is
        the start of the first token.

    7    The wcstok_s function then searches from there for the first wide character in s1 that
         is contained in the current separator wide string. If no such wide character is found, the
         current token extends to the end of the wide string pointed to by s1, and subsequent
         searches in the same wide string for a token return a null pointer. If such a wide character
         is found, it is overwritten by a null wide character, which terminates the current token.

    8    In all cases, the wcstok_s function stores sufficient information in the pointer pointed
         to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
         value for ptr, shall start searching just past the element overwritten by a null wide
         character (if any).
         Returns

    9    The wcstok_s function returns a pointer to the first wide character of a token, or a null
         pointer if there is no token or there is a runtime-constraint violation.

    10   EXAMPLE
                #define _ _STDC_WANT_LIB_EXT1_ _ 1
                #include <wchar.h>
                static wchar_t str1[] = L"?a???b,,,#c";
                static wchar_t str2[] = L"\t \t";
                wchar_t *t, *ptr1, *ptr2;
                rsize_t max1 = wcslen(str1)+1;
                rsize_t max2 = wcslen(str2)+1;
                t = wcstok_s(str1, &max1, "?", &ptr1);                // t points to the token "a"
                t = wcstok_s(NULL, &max1, ",", &ptr1);                // t points to the token "??b"
                t = wcstok_s(str2, &max2, " \t", &ptr2);              // t is a null pointer
                t = wcstok_s(NULL, &max1, "#,", &ptr1);               // t points to the token "c"
                t = wcstok_s(NULL, &max1, "?", &ptr1);                // t is a null pointer

         K.3.9.2.4 Miscellaneous functions
         K.3.9.2.4.1 The wcsnlen_s function
         Synopsis

### K.3.9.3 [Extended multibyte/wide character conversion utilities]

### K.3.9.3.1 [Restartable multibyte/wide character conversion functions]

    1   Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the
        conversion state) to be a null pointer.

### K.3.9.3.1.1 [The wcrtomb_s function]

    2 Synopsis
               #include <wchar.h>
                errno_t wcrtomb_s(size_t * restrict retval,
                     char * restrict s, rsize_t smax,
                     wchar_t wc, mbstate_t * restrict ps);
        Runtime-constraints

    3   Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax
        shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer,
        then smax shall be not be less than the number of bytes to be stored in the array pointed
        to by s. If s is a null pointer, then smax shall equal zero.

    4   If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is
        not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then
        wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then
        wcrtomb_s sets *retval to (size_t)(-1).
        Description

    5   If s is a null pointer, the wcrtomb_s function is equivalent to the call
                        wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps)
        where retval and buf are internal variables of the appropriate types, and the size of
        buf is greater than MB_CUR_MAX.

    6   If s is not a null pointer, the wcrtomb_s function determines the number of bytes
        needed to represent the multibyte character that corresponds to the wide character given
        by wc (including any shift sequences), and stores the multibyte character representation
        in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are
        stored. If wc is a null wide character, a null byte is stored, preceded by any shift
        sequence needed to restore the initial shift state; the resulting state described is the initial
        conversion state.

    7   If wc does not correspond to a valid multibyte character, an encoding error occurs: the
        wcrtomb_s function stores the value (size_t)(-1) into *retval and the
        conversion state is unspecified. Otherwise, the wcrtomb_s function stores into
        *retval the number of bytes (including any shift sequences) stored in the array pointed
        to by s.
        Returns

    8   The wcrtomb_s function returns zero if no runtime-constraint violation and no
        encoding error occurred. Otherwise, a nonzero value is returned.

### K.3.9.3.2 [Restartable multibyte/wide string conversion functions]

    1   Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not
        permit the ps parameter (the pointer to the conversion state) to be a null pointer.

### K.3.9.3.2.1 [The mbsrtowcs_s function]

    2 Synopsis
              #include <wchar.h>
               errno_t mbsrtowcs_s(size_t * restrict retval,
                    wchar_t * restrict dst, rsize_t dstmax,
                    const char ** restrict src, rsize_t len,
                    mbstate_t * restrict ps);
        Runtime-constraints

    3   None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
        then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
        pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
        not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null
        character shall occur within the first dstmax multibyte characters of the array pointed to
        by *src.

    4   If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If
        retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1).
        If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
        then mbsrtowcs_s sets dst[0] to the null wide character.
        Description

    5   The mbsrtowcs_s function converts a sequence of multibyte characters that begins in
        the conversion state described by the object pointed to by ps, from the array indirectly
        pointed to by src into a sequence of corresponding wide characters. If dst is not a null
        pointer, the converted characters are stored into the array pointed to by dst. Conversion
        continues up to and including a terminating null character, which is also stored.
        Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
        not form a valid multibyte character, or (if dst is not a null pointer) when len wide
         characters have been stored into the array pointed to by dst.[453] If dst is not a null
         pointer and no null wide character was stored into the array pointed to by dst, then
         dst[len] is set to the null wide character. Each conversion takes place as if by a call
         to the mbrtowc function.

    Footnote 453) Thus, the value of len is ignored if dst is a null pointer.

    6    If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
         pointer (if conversion stopped due to reaching a terminating null character) or the address
         just past the last multibyte character converted (if any). If conversion stopped due to
         reaching a terminating null character and if dst is not a null pointer, the resulting state
         described is the initial conversion state.

    7    Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
         sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
         the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the
         conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into
         *retval the number of multibyte characters successfully converted, not including the
         terminating null character (if any).

    8    All elements following the terminating null wide character (if any) written by
         mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take
         unspecified values when mbsrtowcs_s returns.[454]

    Footnote 454) This allows an implementation to attempt converting the multibyte string before discovering a
              terminating null character did not occur where required.

    9    If copying takes place between objects that overlap, the objects take on unspecified
         values.
         Returns

    10   The mbsrtowcs_s function returns zero if no runtime-constraint violation and no
         encoding error occurred. Otherwise, a nonzero value is returned.
         K.3.9.3.2.2 The wcsrtombs_s function
         Synopsis

    11            #include <wchar.h>
                  errno_t wcsrtombs_s(size_t * restrict retval,
                       char * restrict dst, rsize_t dstmax,
                       const wchar_t ** restrict src, rsize_t len,
                       mbstate_t * restrict ps);
         Runtime-constraints

    12   None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
         then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
         pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
         not equal zero. If dst is not a null pointer and len is not less than dstmax, then the
         conversion shall have been stopped (see below) because a terminating null wide character
         was reached or because an encoding error occurred.

    13   If there is a runtime-constraint violation, then wcsrtombs_s does the following. If
         retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1).
         If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
         then wcsrtombs_s sets dst[0] to the null character.
         Description

    14   The wcsrtombs_s function converts a sequence of wide characters from the array
         indirectly pointed to by src into a sequence of corresponding multibyte characters that
         begins in the conversion state described by the object pointed to by ps. If dst is not a
         null pointer, the converted characters are then stored into the array pointed to by dst.
         Conversion continues up to and including a terminating null wide character, which is also
         stored. Conversion stops earlier in two cases:
         — when a wide character is reached that does not correspond to a valid multibyte
           character;
         — (if dst is not a null pointer) when the next multibyte character would exceed the
             limit of n total bytes to be stored into the array pointed to by dst. If the wide
             character being converted is the null wide character, then n is the lesser of len or
             dstmax. Otherwise, n is the lesser of len or dstmax-1.
         If the conversion stops without converting a null wide character and dst is not a null
         pointer, then a null character is stored into the array pointed to by dst immediately
         following any multibyte characters already stored. Each conversion takes place as if by a
         call to the wcrtomb function.[455]

    Footnote 455) If conversion stops because a terminating null wide character has been reached, the bytes stored
              include those necessary to reach the initial shift state immediately before the null byte. However, if
              the conversion stops before a terminating null wide character has been reached, the result will be null
              terminated, but might not end in the initial shift state.

    15   If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
         pointer (if conversion stopped due to reaching a terminating null wide character) or the
         address just past the last wide character converted (if any). If conversion stopped due to
         reaching a terminating null wide character, the resulting state described is the initial
         conversion state.

    16   Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
         wide character that does not correspond to a valid multibyte character, an encoding error
         occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval
         and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores
         into *retval the number of bytes in the resulting multibyte character sequence, not
         including the terminating null character (if any).

    17   All elements following the terminating null character (if any) written by wcsrtombs_s
         in the array of dstmax elements pointed to by dst take unspecified values when
         wcsrtombs_s returns.[456]

    Footnote 456) When len is not less than dstmax, the implementation might fill the array before discovering a
              runtime-constraint violation.

    18   If copying takes place between objects that overlap, the objects take on unspecified
         values.
         Returns

    19   The wcsrtombs_s function returns zero if no runtime-constraint violation and no
         encoding error occurred. Otherwise, a nonzero value is returned.

### L. [Annex L (normative) Analyzability]

### L.1 [Scope]

    1   This annex specifies optional behavior that can aid in the analyzability of C programs.

    2   An implementation that defines _ _STDC_ANALYZABLE_ _ shall conform to the
        specifications in this annex.[457]

    Footnote 457) Implementations that do not define _ _STDC_ANALYZABLE_ _ are not required to conform to these
             specifications.

### L.2 [Definitions]

### L.2.1 [Definitions]

    1   out-of-bounds store
        an (attempted) access (3.1) that, at run time, for a given computational state, would
        modify (or, for an object declared volatile, fetch) one or more bytes that lie outside
        the bounds permitted by this Standard.

### L.2.2 [Definitions]

    1   bounded undefined behavior
        undefined behavior (3.4.3) that does not perform an out-of-bounds store.

    2   NOTE 1    The behavior might perform a trap.

    3   NOTE 2    Any values produced or stored might be indeterminate values.

### L.2.3 [Definitions]

    1   critical undefined behavior
        undefined behavior that is not bounded undefined behavior.

    2   NOTE     The behavior might perform an out-of-bounds store or perform a trap.

### L.3 [Requirements]

    1   If the program performs a trap (3.19.5), the implementation is permitted to invoke a
        runtime-constraint handler. Any such semantics are implementation-defined.

    2   All undefined behavior shall be limited to bounded undefined behavior, except for the
        following which are permitted to result in critical undefined behavior:
        — An object is referred to outside of its lifetime (6.2.4).
        — A store is performed to an object that has two incompatible declarations (6.2.7),
        — A pointer is used to call a function whose type is not compatible with the referenced
          type (6.2.7, 6.3.2.3, 6.5.2.2).
        — An lvalue does not designate an object when evaluated (6.3.2.1).
        — The program attempts to modify a string literal (6.4.5).
        — The operand of the unary * operator has an invalid value (6.5.3.2).
        — Addition or subtraction of a pointer into, or just beyond, an array object and an
          integer type produces a result that points just beyond the array object and is used as
          the operand of a unary * operator that is evaluated (6.5.6).
        — An attempt is made to modify an object defined with a const-qualified type through
          use of an lvalue with non-const-qualified type (6.7.3).
        — An argument to a function or macro defined in the standard library has an invalid
          value or a type not expected by a function with variable number of arguments (7.1.4).
        — The longjmp function is called with a jmp_buf argument where the most recent
          invocation of the setjmp macro in the same invocation of the program with the
          corresponding jmp_buf argument is nonexistent, or the invocation was from another
          thread of execution, or the function containing the invocation has terminated
          execution in the interim, or the invocation was within the scope of an identifier with
          variably modified type and execution has left that scope in the interim (7.13.2.1).
        — The value of a pointer that refers to space deallocated by a call to the free or realloc
          function is used (7.22.3).
        — A string or wide string utility function accesses an array beyond the end of an object
          (7.24.1, 7.29.4).