Hi, I ran into a rather interesting issue today. I noticed that if I run (with GCC 12.1) gcc -x c -std=c17 -dM -E foo.c where foo.c is simply #include <features.h> I don't get any of the XOPEN, POSIX or BSD defines that features.h would typically set based on -D options passed to the compiler. However, if I run gcc -x c++ -std=c++17 -dM -E foo.c I get definitions like #define _XOPEN_SOURCE 700. I find this curious - I thought compilers were supposed to be OS standards agnostic (but obviously not language standards agnostic). I am using a glibc 2.17 system, if that makes any difference. I don't see anything in features.h that would indicate _XOPEN_SOURCE should be defined if the compiler is a C++ compiler conforming to the C++17 standard (for instance). Any ideas as to what is going on here? Is this expected behavior, as in something in the C++ standard I am unaware of, or is it a bug? Thanks, Tom
