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\n", 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\n", tvDiff.tv_sec, tvDiff.tv_usec);      return 0; } 

Answer 2

Another option ( at least on some UNIX ) is clock_gettime and related functions. These allow access to various realtime clocks and you can select one of the higher resolution ones and throw away the resolution you don't need.