Measure time elapsed in C++

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fast elapsed time on linux

How can I measure how long a function takes to execute in C++? It would be best if I could get the time to a fraction of a millisecond, but if not accuracy to one millisecond should be good enough. I'm running Ubuntu 11.04 if that means anything.

score 5 · Answer 1 · answered Jun 24 '11 at 20:36

The best clock for performance measurement is system-wide real-time clock. In Linux, you can use clock_gettime function with CLOCK_MONOTONIC or CLOCK_MONOTONIC_RAW. Those will give you nanosecond precision.

score -2 · Accepted Answer · edited Jun 27 '14 at 05:33

-2

#include <ctime>
int main(){
    clock_t start = clock();
    // your program goes here
    clock_t ends = clock();
    cout << "Time elapsed: " << (double) (ends - start) / CLOCKS_PER_SEC << endl;
    return 0;
}

edited Jun 27 '14 at 05:33

ʇolɐǝz ǝɥʇ qoq

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answered Jun 24 '11 at 20:35

Benny Tjia

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This is very low precision approximation rather than elapsed time. Division by CLOCKS_PER_SEC also looks odd as this is a hard-coded macro that doesn't really represent a number of clocks per second. Plus, it is not a wall clock. So if you real-time process was swapped out, it will give you some totally weird results... :-] – Jun 24 '11 at 20:39
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How accurate is that going to be? – John Stimac Jun 24 '11 at 20:41
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@Vlad: clock_gettime is an adequate alternative i guess.. – Benny Tjia Jun 24 '11 at 20:44
This works for me pretty accurately, but it's definitely not the best way to do this. – ʇolɐǝz ǝɥʇ qoq Jun 27 '14 at 05:33

Measure time elapsed in C++

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