http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60498
--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> --- Definitely a Cygwin bug, their header should test: #if !defined(__STRICT_ANSI__) || (__STDC_VERSION__ >= 199901L) || (__cplusplus >= 201103L) That way the functions will be defined for any -std=gnuNN mode, for C99, and for C++11, which would be correct.