Calculate time difference

#include <time.h>double difftime(time_ttime1, time_ttime0);

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).

The **difftime**() function is thread-safe.

SVr4, 4.3BSD, C89, C99.

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.

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