问题
when I use clock_gettime in my code snippet, and compile with flag -std=c99, I got a error like this:
warning: implicit declaration of function 'clock_gettime'
error: 'CLOCK_REALTIME' undeclared (first use in this function)
and I have included the file 'time.h'. anyone knows how to fix it.
回答1:
in your original code with -std=c99, try adding
#define _POSIX_C_SOURCE >= 199309L
the man page for clock_gettime indicates this is a necessary feature test macro requirement.
来源：https://stackoverflow.com/questions/13069758/got-compile-error-when-use-clock-gettime-in-c99