Measuring time in C gives wrong result

Question

I am trying to measure time in C in microseconds. I tried this code, but the value time_passed is a huge number, instead of 0 (or 1).

   struct timeval start;
   settimeofday(&start,NULL);
   struct timeval stop;
   settimeofday(&stop,NULL);
   unsigned long long int time_passed = 
       (stop.tv_sec-start.tv_sec)*1000000 + (stop.tv_usec - start.tv_usec);
   printf("time passed: %llu us\n",time_passed);

There is not statement between your start and stop. Only a declaration. — wildplasser, May 04 '16 at 11:11
He means there is nothing to compute between `start` and `stop` — David Ranieri, May 04 '16 at 11:13
You are not checking return values of functions. It looks like you don't care whether your calls sucseed or fail. — n. m. could be an AI, May 04 '16 at 11:16
@n.m.: But in the true spirit of C programming, the code gets to the end as quickly as possible! — John Zwinck, May 04 '16 at 11:22

score 7 · Accepted Answer · answered May 04 '16 at 11:12

7

You are calling settimeofday() when you should be calling gettimeofday()!

answered May 04 '16 at 11:12

John Zwinck

239,568
38
324
436

Measuring time in C gives wrong result

1 Answers1