C/time.h/clock
clock: returns time or -1 if the time is not available
//Declaration: clock_t clock(void);
//To transform this value into seconds, divide it by CLOCKS_PER_SEC.
#include <time.h>
#include <stdio.h>
int main(void)
{
printf("Elapsed time: %u secs.\n", clock()/CLOCKS_PER_SEC);
}
/*
Elapsed time: 0 secs.
*/