gettimeofday example

#include <sys/time.h>

...
    struct timeval begin, end;
    gettimeofday(&start, NULL);

    <COMPUTATION>

    gettimeofday(&end, NULL);
    double elapsed_sec = (double)(end.tv_sec - begin.tv_sec) + ((double)(end.tv_usec - begin.tv_usec))/1000000.0;
...