On Sat, 10 Feb 2018, Zack Weinberg wrote: > +#if defined __USE_ISOC99 || defined __USE_XOPEN2K That's equivalent to just #ifdef __USE_ISOC99 (since __USE_XOPEN2K implies __USE_ISOC99; POSIX.1-2001 is based on C99). -- Joseph S. Myers joseph@codesourcery.com