http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51749
--- Comment #20 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jakub Jelinek from comment #19) > Has anyone checked recently what exactly we still need -D_GNU_SOURCE for in > the public headers (as opposed to just the libstdc++ code), as compared to > say _ISOC99_SOURCE for glibc, at least for C++11? I haven't checked, it would be useful to do so. There is some stuff used by the --enable-clocale=gnu code such as uselocale (which is now part of POSIX but not C99) but it might be possible to only require that from .cc files not in headers.