How to get the time elapsed in C in milliseconds? (Windows)

The solution below seems OK to me. What do you think?

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

long timediff(clock_t t1, clock_t t2) {
    long elapsed;
    elapsed = ((double)t2 - t1) / CLOCKS_PER_SEC * 1000;
    return elapsed;
}

int main(void) {
    clock_t t1, t2;
    int i;
    float x = 2.7182;
    long elapsed;

    t1 = clock();
    for (i=0; i < 1000000; i++) {
           x = x * 3.1415; 
    }
    t2 = clock();

    elapsed = timediff(t1, t2);
    printf("elapsed: %ld ms\n", elapsed);


    return 0;
}

Reference: http://www.acm.uiuc.edu/webmonkeys/book/c_guide/2.15.html#clock

For Windows, GetSystemTime() is what you want. For POSIX, gettimeofday().

A cross platform way is to use ftime.

Windows specific link here: http://msdn.microsoft.com/en-us/library/aa297926(v=vs.60).aspx

Example below.

#include <stdio.h>
#include <sys\timeb.h> 

int main()     
{ 
    struct timeb start, end;
    int diff;
    int i = 0;
    ftime(&start);

    while(i++ < 999) {
        /* do something which takes some time */
        printf(".");    
    }

    ftime(&end);
    diff = (int) (1000.0 * (end.time - start.time)
        + (end.millitm - start.millitm));

    printf("\nOperation took %u milliseconds\n", diff);
    return 0;
}

I ran the code above and traced through it using VS2008 and saw it actually calls the windows GetSystemTimeAsFileTime function.

Anyway, ftime will give you milliseconds precision.