17 Language support library [support]

17.14 C headers [support.c.headers]

17.14.1 General [support.c.headers.general]

For compatibility with the C standard library, the C++ standard library provides the C headers shown in Table 44.
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 ISO C. Source files that are not intended to also be valid ISO 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 ISO 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 <stdbool.h> // for bool in C, no effect in C++ #include <stddef.h> // for size_t #ifdef __cplusplus // see [cpp.predefined] extern "C" // see [dcl.link] #endif void f(bool b[], size_t n); — end example]
Table 44: C headers [tab:c.headers]