//計算所花時間(微秒) GCC

#include <stdio.h>
#include <sys/time.h>
void tvsub(struct timeval *tdiff,
      const struct timeval *t1,
      const struct timeval *t0)
{
        tdiff->tv_sec = t1->tv_sec - t0->tv_sec;
        tdiff->tv_usec = t1->tv_usec - t0->tv_usec;
        if (tdiff->tv_usec < 0)
                tdiff->tv_sec--, tdiff->tv_usec += 1000000;
}

void print_time(const struct timeval *t0, const struct timeval *t1)
{
        struct timeval td;
        double s;
        tvsub(&td, t1, t0);
        s = td.tv_sec + (td.tv_usec / 1000000.);
        printf("It cost %.3lf secs.\n", s);
}

int main(void)
{
        struct timeval start, stop;
        int i;

        gettimeofday(&start, (struct timezone *)0);
        for(i=0; i<10000; i++) printf("%d\n", i);
        //do something here!!!!
        gettimeofday(&stop, (struct timezone *)0);

        print_time(&start, &stop);
        return 0;
}