cppdraft_translate/cppdraft/support/c/headers.md

[support.c.headers]

17 Language support library [support]

17.15 C headers [support.c.headers]

17.15.1 General [support.c.headers.general]

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For compatibility with theC standard library, the C++ standard library provides the C headers shown in Table 47.

The intended use of these headers is for interoperability only.

It is possible that C++ source files need to include one of these headers in order to be valid C. Source files that are not intended to also be valid C should not use any of the C headers.

[Note 1:

The C headers either have no effect, such as <stdbool.h> and <stdalign.h>, or otherwise the corresponding header of the form <cname> provides the same facilities and assuredly defines them in namespace std.

— end note]

[Example 1:

The following source file is both valid C++ and valid C. Viewed as C++, it declares a function with C language linkage; viewed as C it simply declares a function (and provides a prototype).

#include <uchar.h> // for char8_t in C, not necessary in C++#include <stddef.h> // for size_t#ifdef __cplusplus // see [cpp.predefined]extern "C" // see [dcl.link]#endifvoid f(char8_t s[], size_t n); — end example]

Table 47 — C headers [tab:c.headers]

🔗 <assert.h>	<inttypes.h>	<signal.h>	<stdckdint.h>	<tgmath.h>
🔗 <complex.h>	<iso646.h>	<stdalign.h>	<stddef.h>	<time.h>
🔗 <ctype.h>	<limits.h>	<stdarg.h>	<stdint.h>	<uchar.h>
🔗 <errno.h>	<locale.h>	<stdatomic.h>	<stdio.h>	<wchar.h>
🔗 <fenv.h>	<math.h>	<stdbit.h>	<stdlib.h>	<wctype.h>
🔗 <float.h>	<setjmp.h>	<stdbool.h>	<string.h>

17.15.2 Header <complex.h> synopsis [complex.h.syn]

🔗

#include

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The header <complex.h> behaves as if it simply includes the header.

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[Note 1:

Names introduced by in namespace std are not placed into the global namespace scope by <complex.h>.

— end note]

17.15.3 Header <iso646.h> synopsis [iso646.h.syn]

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The C++ header <iso646.h> is empty.

[Note 1:

and,and_eq,bitand,bitor,compl,not_eq,not,or,or_eq,xor, andxor_eq are keywords in C++ ([lex.key]).

— end note]

17.15.4 Header <stdalign.h> synopsis [stdalign.h.syn]

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The contents of the C++ header <stdalign.h> are the same as the C standard library header <stdalign.h>.

See also: ISO/IEC 9899:2024, 7.15

17.15.5 Header <stdbool.h> synopsis [stdbool.h.syn]

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The contents of the C++ header <stdbool.h> are the same as the C standard library header <stdbool.h>.

See also: ISO/IEC 9899:2024, 7.19

17.15.6 Header <tgmath.h> synopsis [tgmath.h.syn]

🔗

#include #include

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The header <tgmath.h> behaves as if it simply includes the headers and.

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[Note 1:

The overloads provided in C by type-generic macros are already provided in and by “sufficient” additional overloads.

— end note]

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[Note 2:

Names introduced by or in namespace std are not placed into the global namespace scope by <tgmath.h>.

— end note]

17.15.7 Other C headers [support.c.headers.other]

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Every C header other than<complex.h>,<iso646.h>,<stdalign.h>,
<stdatomic.h>,<stdbit.h>,<stdbool.h>,<stdckdint.h>, and
<tgmath.h>, each of which has a name of the form<name.h>, behaves as if each name placed in the standard library namespace by the corresponding<cname> header is placed within the global namespace scope, except for the functions described in [sf.cmath], the std​::​lerp function overloads ([c.math.lerp]), the declaration of std​::​byte ([cstddef.syn]), and the functions and function templates described in [support.types.byteops].

It is unspecified whether these names are first declared or defined within namespace scope ([basic.scope.namespace]) of the namespacestd and are then injected into the global namespace scope by explicit using-declarations ([namespace.udecl]).

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[Example 1:

The header assuredly provides its declarations and definitions within the namespacestd.

It may also provide these names within the global namespace.

The header <stdlib.h> assuredly provides the same declarations and definitions within the global namespace, much as in ISO/IEC 9899.

It may also provide these names within the namespace std.

— end example]