unix - Calculating elapsed time in a C program in milliseconds

Question

I want to calculate the time in milliseconds taken by the execution of some part of my program. I've been looking online, but there's not much info on this topic. Any of you know how to do this?

Answer 1

Best way to answer is with an example:

#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

/* Return 1 if the difference is negative, otherwise 0.  */
int timeval_subtract(struct timeval *result, struct timeval *t2, struct timeval *t1)
{
    long int diff = (t2->tv_usec + 1000000 * t2->tv_sec) - (t1->tv_usec + 1000000 * t1->tv_sec);
    result->tv_sec = diff / 1000000;
    result->tv_usec = diff % 1000000;

    return (diff<0);
}

void timeval_print(struct timeval *tv)
{
    char buffer[30];
    time_t curtime;

    printf("%ld.%06ld", tv->tv_sec, tv->tv_usec);
    curtime = tv->tv_sec;
    strftime(buffer, 30, "%m-%d-%Y  %T", localtime(&curtime));
    printf(" = %s.%06ld
", buffer, tv->tv_usec);
}

int main()
{
    struct timeval tvBegin, tvEnd, tvDiff;

    // begin
    gettimeofday(&tvBegin, NULL);
    timeval_print(&tvBegin);

    // lengthy operation
    int i,j;
    for(i=0;i<999999L;++i) {
        j=sqrt(i);
    }

    //end
    gettimeofday(&tvEnd, NULL);
    timeval_print(&tvEnd);

    // diff
    timeval_subtract(&tvDiff, &tvEnd, &tvBegin);
    printf("%ld.%06ld
", tvDiff.tv_sec, tvDiff.tv_usec);

    return 0;
}