difftime, difftime64 - compute difference between two calendar time values

Syntax	#include <time.h> double difftime(time_t time1, time_t time0); double difftime64(time64_t time1, time64_t time0);
Description	time1 and time0 are time values of type time_t or time64_t. These time values are supplied by the mktime(), mktime64() and time(), time64() functions.
Return val.	time1 - time0	if successful. The time difference is indicated in seconds and is of type double.
See also	ctime(), mktime(), time(), time.h.