The GCC manual says: If you need a Standard compliant library, then you need to find one, as GCC does not provide one. The GNU C library (called 'glibc') provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and HURD-based GNU systems; no recent version of it supports other systems, though some very old versions did. Version 2.2 of the GNU C library includes nearly complete C99 support. You could also ask your operating system vendor if newer libraries are available.
However, even if the GNU C library is used, GCC also provides some builtins, and it is not clear whether when there is a difference between ISO C and POSIX (e.g. an undefined behavior in C and some defined behavior in POSIX), the GCC builtin just conforms to ISO C, or also conforms to POSIX. So, IMHO, some clarification is needed. An example is remquo(x,y,*quo) when y ≠ 0 and the result is NaN. ISO C currently fails to define the behavior concerning *quo, making this call undefined behavior. But in POSIX, this call is valid and *quo just takes an (implicitly) unspecified value[*]. [*] https://austingroupbugs.net/view.php?id=713 -- Vincent Lefèvre <vinc...@vinc17.net> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
