test clock() in c. from http://www.acm.uiuc.edu/webmonkeys/book/c_guide/2.15.html#clock.

clock_t.c

#include<time.h>
#include<stdio.h>

int main(void)
{
    clock_t ticks1, ticks2;

    ticks1=clock();
    ticks2=ticks1;
    while((ticks2-ticks1)/CLOCKS_PER_SEC<1) {
        ticks2=clock();
    }

    printf("Took %ld ticks to wait one second.\n",ticks2-ticks1);
    printf("This value should be the same as CLOCKS_PER_SEC which is %ld.\n",CLOCKS_PER_SEC);
    return 0;
}