Main Example

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>
#ifdef __MACH__
#include <mach/clock.h>
#include <mach/mach.h>
#endif

#define MAXBUF 10

static void gettime (struct timespec *t) {
#ifdef __MACH__
    clock_serv_t cclock;
    mach_timespec_t mts;
    host_get_clock_service(mach_host_self(), REALTIME_CLOCK, &cclock);
    clock_get_time(cclock, &mts);
    mach_port_deallocate(mach_task_self(), cclock);
    t->tv_sec = mts.tv_sec;
    t->tv_nsec = mts.tv_nsec;
#else
    clock_gettime(CLOCK_REALTIME, t);
#endif
}

int main (void) {
    FILE *fp;
    struct timespec tic, toc;
    char *executableName = "./a.out";
    char answer[MAXBUF];

    gettime(&tic);
    if ((fp = popen(executableName, "r")) == NULL) {
        fprintf(stderr, "The file couldn't be opened.\n");
        return 1;
    }
    gettime(&toc);

    fgets(answer, MAXBUF, fp);
    double elapsed = (double)(toc.tv_nsec - tic.tv_nsec) / 1000000000;
    fprintf(stdout, "The program says %s, and took %fs to run!\n", answer, elapsed);

    pclose(fp);
    return 0;
}