difftime(3) - Linux man page
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. Each of the times is specified in calendar time, which means its value is a measurement (in seconds) relative to
the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
Conforming to
SVr4, 4.3BSD, C89, C99.
Notes
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)