[headers] (original) (raw)

16 Library introduction [library]

16.4 Library-wide requirements [requirements]

16.4.2 Library contents and organization [organization]

16.4.2.3 Headers [headers]

Each element of the C++ standard library is declared or defined (as appropriate) in a.148

The C++ standard library provides the, shown in Table 24.

The facilities of the C standard library are provided in theadditional headers shown in Table 25.149

The headers listed in Table 24, or, for a freestanding implementation, the subset of such headers that are provided by the implementation, are collectively known as the .

[Note 1:

Importable C++ library headers can be imported ([module.import]).

— _end note_]

[Example 1: import <vector>; std::vector<int> vi; — _end example_]

Except as noted in [library] through [exec]and [depr], the contents of each header c_name_ is the same as that of the corresponding header name.h as specified in the C standard library.

In the C++ standard library, however, the declarations (except for names which are defined as macros in C) are withinnamespace scope of the namespace std.

It is unspecified whether these names (including any overloads added in[support] through [exec] and [depr]) are first declared within the global namespace scope and are then injected into namespace std by explicitusing-declarations ([namespace.udecl]).

Names which are defined as macros in C shall be defined as macros in the C++ standard library, even if C grants license for implementation as functions.

[Note 2:

The names defined as macros in C include the following:assert, offsetof, setjmp, va_arg,va_end, and va_start.

— _end note_]

Names that are defined as functions in C shall be defined as functions in the C++ standard library.150

Identifiers that are keywords or operators in C++ shall not be defined as macros in C++ standard library headers.151

Subclause [support.c.headers] describes the effects of using the name.h (C header) form in a C++ program.[152](#footnote-152 "The ".h" headers dump all their names into the global namespace, whereas the newer forms keep their names in namespace std. Therefore, the newer forms are the preferred forms for all uses except for C++ programs which are intended to be strictly compatible with C.")

ISO/IEC 9899:2018, Annex K describes a large number of functions, with associated types and macros, which “promote safer, more secure programming” than many of the traditional C library functions.

The names of the functions have a suffix of _s; most of them provide the same service as the C library function with the unsuffixed name, but generally take an additional argument whose value is the size of the result array.

If any C++ header is included, it is implementation-defined whether any of these names is declared in the global namespace.

(None of them is declared in namespace std.)

Table 26 lists the Annex K names that may be declared in some header.

These names are also subject to the restrictions of [macro.names].

Table 26: Names from ISO/IEC 9899:2018, Annex K [tab:c.annex.k.names]