https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24012
--- Comment #21 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #19) > (In reply to Gerald Pfeifer from comment #4) > > Historically, on some systems one had to define _POSIX_C_SOURCE to get at > > fileno(), which has been used by code generated by flex() and probably > > others. > > Yes, but you don't have to define it to 1. If you define _POSIX_C_SOURCE to > 199506L or set _XOPEN_SOURCE to 500 then I think the functions we use are > available, as well as fileno. Correction: _POSIX_C_SOURCE=200112L or _XOPEN_SOURCE=600 should declare them.
