difftime − calculate time difference

#include <time.h>

double difftime(time_t time1, time_t time0);

The difftime() function returns the number of seconds elapsed between time time1 and time time0, represented as a double. The two times are specified in calendar time, which represents the time elapsed since the Epoch (00:00:00 on January 1, 1970, Coordinated Universal Time (UTC)).

SVID 3, BSD 4.3, ISO 9899

This function is required by ANSI C. On a POSIX system, time_t is an arithmetic type, and one could just define

#define difftime(t1,t0) (double)(t1 - t0)

when the possible overflow in the subtraction is not a concern.

date(1), gettimeofday(2), time(2), ctime(3), gmtime(3), localtime(3)