B.22 Date and time <time.h>

NULL                  size_t                  time_t
CLOCKS_PER_SEC        clock_t                 struct tm

clock_t clock(void);
double difftime(time_t time1, time_t time0);
time_t mktime(struct tm *timeptr);
time_t time(time_t *timer);
char *asctime(const struct tm *timeptr);
char *ctime(const time_t *timer);
struct tm *gmtime(const time_t *timer);
struct tm *localtime(const time_t *timer);
size_t strftime(char *restrict s, size_t maxsize, const char *restrict format,
                const struct tm *restrict timeptr);