Boost returning CPU time of 0

Question

I'm trying to measure the CPU time for functions within my C++ program. I am doing this using the boost library. When I run my program however I get a result of 0 seconds. I'm new to boost so if someone could point me in the right direction?

How can I make this return a time that I can actually use, such as 0.00156 or something?

Code: Inside main()

boost::timer::cpu_timer timer;

std::cout << tree1.search("Cork") << std::endl;

//Print CPU TIME
boost::timer::cpu_times elapsed = timer.elapsed();
std::cout << " CPU TIME: " << (elapsed.user + elapsed.system) / 1e9 << " seconds" << std::endl;

What happens if you write `double(1e9)` instead of just `1e9`? — Xirema, Mar 20 '17 at 21:06
Have you tried printing out the raw values returned for `elapsed.user` and `elapsed.system`? What do you get? — Xirema, Mar 20 '17 at 21:09
Perhaps your timer resolution is really coarse and the job takes less than one tick. — n. m. could be an AI, Mar 20 '17 at 21:18
Try `for( int i=0; i < SomeBigNumber; ++i ) { std::cout << tree1.search("Cork") << std::endl; }` and see if that makes any difference. I've found precision of `boost::timer::cpu_timer` to be quite low on my machine, unless the code to be tested runs for a few seconds at least. — zett42, Mar 20 '17 at 21:32
@FredLarson tree1 is a BST with 50 nodes that contains a city object — luke_k, Mar 20 '17 at 21:37
So that shouldn't take more than 6 comparisons to find a match (assuming it's balanced). Probably not enough time to exceed a timer tick. — Fred Larson, Mar 20 '17 at 21:40
@zett42 it works, fudges the numbers a bit but I suppose if I do the same thing to all the functions I need to test it'll even out. — luke_k, Mar 20 '17 at 21:45

Rama · Answer 1 · 2017-03-20T21:20:01.580

1

You can use boost chrono;

boost::timer::cpu_timer timer;

std::cout << tree1.search("Cork") << std::endl;

//Print CPU TIME
boost::chrono::duration<double> elapsed = boost::chrono::nanoseconds(timer.elapsed().user);
std::cout << " CPU TIME: " << seconds.count() << "s\n" << " seconds" << std::endl;

edited Mar 20 '17 at 21:20

answered Mar 20 '17 at 21:15

Rama

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That still makes no difference. Could it be that the function just doesn't take long enough to execute and the CPU time is so small that it can't be displayed? – luke_k Mar 20 '17 at 21:18
While it's a good idea to use `chrono` instead of Boost. I doubt it has better time resolution. I wouldn't expect this to make any difference. – Fred Larson Mar 20 '17 at 21:28

Boost returning CPU time of 0

1 Answers1