redhat man page for difftime

DIFFTIME(3)						     Linux Programmer's Manual						       DIFFTIME(3)

NAME
       difftime - calculate time difference

SYNOPSIS
       #include <time.h>

       double difftime(time_t time1, time_t time0);

DESCRIPTION
       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)).

CONFORMING TO
       SVID 3, BSD 4.3, ISO 9899

NOTES
       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.

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

GNU
								    1993-07-02							       DIFFTIME(3)