Timing a function in microseconds

Question

Hey guys I'm trying to time some search functions I wrote in microseconds, and it needs to take long enough to get it to show 2 significant digits. I wrote this code to time my search function but it seems to go too fast. I always end up getting 0 microseconds unless I run the search 5 times then I get 1,000,000 microseconds. I'm wondering if I did my math wrong to get the time in micro seconds, or if there's some kind of formatting function I can use to force it to display two sig figs?

clock_t start = clock();
index = sequentialSearch.Sequential(TO_SEARCH);
index = sequentialSearch.Sequential(TO_SEARCH);
clock_t stop = clock();
cout << "number found at index " << index << endl;
int time = (stop - start)/CLOCKS_PER_SEC;
time = time * SEC_TO_MICRO;
cout << "time to search = " << time<< endl;

yeah, I plan on adding that later, right now I'm just trying to get it to work. — Jonathan, Feb 21 '12 at 21:55
The usual `clock()` resolution is something like 10ms, though, so that might not be sufficient. Check out ``'s high-resolution clock if you need more precision. — Kerrek SB, Feb 21 '12 at 22:03

score 3 · Answer 1 · answered Feb 21 '12 at 21:46

3

You are using integer division on this line:

int time = (stop - start)/CLOCKS_PER_SEC;

I suggest using a double or float type, and you'll likely need to cast the components of the division.

answered Feb 21 '12 at 21:46

Matt T

511
2
8

yeah that solved it. I should've seen that. Thanks for pointing it out. – Jonathan Feb 21 '12 at 22:00

score 0 · Answer 2 · answered Feb 21 '12 at 21:47

0

Use QueryPerformanceCounter and QueryPerformanceFrequency, assuming your on windows platform

here a link to ms KB How To Use QueryPerformanceCounter to Time Code

answered Feb 21 '12 at 21:47

Dampsquid

2,456
15
14

Timing a function in microseconds

2 Answers2