C++ Standard Library header files

The interface of C++ standard library is defined by the following collection of header files

C compatibility headers

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).

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.

Unsupported C headers

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

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. The use of all these headers is deprecated in C++.

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++.

See also