#include <stdio.h>
#include <stdlib.h>
#include <sys/times.h>
#include <unistd.h>

/* return real time in seconds since start of the process */
double walltime() {
   static clock_t ticks_per_second = 0;
   if (!ticks_per_second) {
      ticks_per_second = sysconf(_SC_CLK_TCK);
   }
   struct tms timebuf;
   /* times returns the number of real time ticks passed since start */
   return (double) times(&timebuf) / ticks_per_second;
}

int main() {
   double t0 = walltime();
   sleep(1);
   double t1 = walltime() - t0;
   printf("sleep(1) took actually %.4lf seconds\n", t1);
}