С datetime functions

c_datetime.md

<sys/time.h>

int gettimeofday(struct timeval *restrict tv, struct timezone *restrict tz);

<time.h>

int clock_gettime(clockid_t clockid, struct timespec *tp);
int timespec_get(struct timespec *ts, int base);

base: TIME_UTC

Datetime Structures

struct timespec {
  time_t   tv_sec;        /* seconds */
  long     tv_nsec;       /* nanoseconds */
};