Not in POSIX yet, but we expect it will be. ISO C11 (latest free draft http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf) sections 7.23.
Gnulib module: stdnoreturn
Portability problems fixed by Gnulib:
<process.h>, on some platforms: MSVC/clang.
Portability problems not fixed by Gnulib:
<stdnoreturn.h>should be #included before ‘_Noreturn’ is used.
_Noreturnis a reserved word; it might be a macro.
lintis defined, standard headers define
noreturn) to be a macro that expands to the empty token sequence on some platforms: Cygwin 2.5.1, FreeBSD 10.3.
noreturnexpands to the empty token sequence, to avoid problems with standard headers that use
noreturnin combination with
__declspec. Although the resulting code operates correctly, the compiler is not informed whether
noreturnfunctions do not return, so it may generate incorrect warnings at compile-time, or code that is slightly less optimized. This problem does not occur with
noreturnbefore the returned type in a declaration, and therefore rejects valid but unusually-worded declarations such as
void _Noreturn foo (void);.