Difference between revisions of "cpp/header"

For some of the C standard library headers of the form xxx.h, the C++ standard library both includes an identically-named header and another header of the form cxxx (all meaningful cxxx headers are listed above). The intended use of headers of form xxx.h is for interoperability only. It is possible that C++ source files need to include one of these headers in order to be valid ISO C. Source files that are not intended to also be valid ISO C should not use any of the C headers.

With the exception of complex.h, each xxx.h header included in the C++ standard library places in the global namespace each name that the corresponding cxxx header would have placed in the std namespace.

These headers are allowed to also declare the same names in the std namespace, and the corresponding cxxx headers are allowed to also declare the same names in the global namespace: including <cstdlib> definitely provides std::malloc and may also provide ::malloc. Including <stdlib.h> definitely provides ::malloc and may also provide std::malloc. This applies even to functions and function overloads that are not part of C standard library.

Notes: xxx.h headers are deprecated in C++98 and undeprecated in C++23. These headers are discouraged for pure C++ code, but not subject to future removal.

<assert.h>	Behaves same as `<cassert>`[edit]
<ctype.h>	Behaves as if each name from `<cctype>` is placed in global namespace[edit]
<errno.h>	Behaves same as `<cerrno>`[edit]
<fenv.h> (C++11)	Behaves as if each name from `<cfenv>` is placed in global namespace[edit]
<float.h>	Behaves same as `<cfloat>`[edit]
<inttypes.h> (C++11)	Behaves as if each name from `<cinttypes>` is placed in global namespace[edit]
<limits.h>	Behaves same as `<climits>`[edit]
<locale.h>	Behaves as if each name from `<clocale>` is placed in global namespace[edit]
<math.h>	Behaves as if each name from `<cmath>` is placed in global namespace, except for names of mathematical special functions[edit]
<setjmp.h>	Behaves as if each name from `<csetjmp>` is placed in global namespace[edit]
<signal.h>	Behaves as if each name from `<csignal>` is placed in global namespace[edit]
<stdarg.h>	Behaves as if each name from `<cstdarg>` is placed in global namespace[edit]
<stddef.h>	Behaves as if each name from `<cstddef>` is placed in global namespace, except for names of `std::byte` and related functions[edit]
<stdint.h> (C++11)	Behaves as if each name from `<cstdint>` is placed in global namespace[edit]
<stdio.h>	Behaves as if each name from `<cstdio>` is placed in global namespace[edit]
<stdlib.h>	Behaves as if each name from `<cstdlib>` is placed in global namespace[edit]
<string.h>	Behaves as if each name from `<cstring>` is placed in global namespace[edit]
<time.h>	Behaves as if each name from `<ctime>` is placed in global namespace[edit]
<uchar.h> (C++11)	Behaves as if each name from `<cuchar>` is placed in global namespace[edit]
<wchar.h>	Behaves as if each name from `<cwchar>` is placed in global namespace[edit]
<wctype.h>	Behaves as if each name from `<cwctype>` is placed in global namespace[edit]

[edit] Special C compatibility headers

The header <stdatomic.h> declares names which are also provided in the C standard library, and defines the _Atomic macro which is a keyword in C. Unlike other xxx.h headers, corresponding <cstdatomic> is not provided.

<stdatomic.h>

(C++23)

Defines _Atomic and provides corresponding components in the C standard library[edit]

[edit] Empty C headers

The headers <complex.h>, <ccomplex>, <tgmath.h>, and <ctgmath> do not contain any content from the C standard library and instead merely include other headers from the C++ standard library.

<ccomplex> (C++11)(deprecated in C++17)(removed in C++20)	Simply includes the header `<complex>`[edit]
<complex.h> (C++11)	Simply includes the header `<complex>`[edit]
<ctgmath> (C++11)(deprecated in C++17)(removed in C++20)	Simply includes the headers `<complex>` and `<cmath>`: the overloads equivalent to the contents of the C header `tgmath.h` are already provided by those headers[edit]
<tgmath.h> (C++11)	Simply includes the headers `<complex>` and `<cmath>`[edit]

[edit] Meaningless C headers

The headers <ciso646>, <cstdalign>, and <cstdbool> are meaningless in C++ because the macros they provide in C are language keywords in C++.

<ciso646> (removed in C++20)	Empty header. The macros that appear in `iso646.h` in C are keywords in C++[edit]
<cstdalign> (C++11)(deprecated in C++17)(removed in C++20)	Defines one compatibility macro constant[edit]
<cstdbool> (C++11)(deprecated in C++17)(removed in C++20)	Defines one compatibility macro constant[edit]
<iso646.h>	Has no effect[edit]
<stdalign.h> (C++11)	Defines one compatibility macro constant[edit]
<stdbool.h> (C++11)	Defines one compatibility macro constant[edit]

[edit] Unsupported C headers

The C headers <stdatomic.h>,(until C++23) <stdnoreturn.h>, and <threads.h> are not included in C++ and have no cxxx equivalents.

[edit] Experimental libraries

C++ TR's/TS's also define several collections of headers.

[edit] See also

C documentation for C Standard Library headers

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Containers library
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Algorithms library
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Difference between revisions of "cpp/header"

Latest revision as of 18:43, 16 October 2024

Contents

Multi-purpose headers

Language support library

Concepts library

Diagnostics library

Memory management library

Metaprogramming library

General utilities library

Containers library

Iterators library

Ranges library

Algorithms library

Strings library

Text processing library

Numerics library

Time library

Input/output library

Concurrency support library

[edit] C compatibility headers