https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57025
--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Alan Coopersmith from comment #11) > While Solaris 11.3 support has been dropped from gcc now, Jonathan Perkins > from pkgsrc found that just removing the definition of __STDC_VERSION__ > didn't work with some of the illumos headers: > https://github.com/jperkin/notes/blob/main/gcc-cpp-stdc/README.md So the illumos sys/feature_tests.h is using __STD_VERSION__ to mean "the version of the C library to expose for the current language mode", whether that language mode is a C language mode or a C++ one. And that's an entirely reasonable use of it IMHO, and conforms to the C++ standard. I stick by what I said in comment 4: code which assumes that __STDC_VERSION__ being defined implies a C compiler is being used is **broken C++ code**. There is no compliance requirement why GCC should stop defining __STDC_VERSION__, and there's a good reason to keep defining it if defining it is needed (or just helpful) for a target's libc headers. The Cython code quoted in the illumos notes should be fixed to check the __cplusplus condition first, then if __cplusplus is not defined check __STDC_VERSION__. It's just bad code. N.B. since C++23 #include <stdatomic.h> works in C++ anyway: https://wg21.link/P0943R6
