Calculate execution time of a function in c++ (visual studio 2010)

Question

I am coding in c++ and working on Visual Studio 2010. I am trying to compute the time that a function takes to execute, here is my code

        double sum=0;   
        clock_t start_s=clock();
        for(int j=1;j<size;j++)
        {
            int key=data[j];
            int i=j-1;
            while(i>=0 && data[i]>key)
            {
                data[i+1]=data[i];
                i=i-1;
            }
            data[i+1]=key;
        }
        clock_t stop_s=clock();
        sum=((double)(stop_s - start_s)/CLOCKS_PER_SEC);

but the problem is that the time computes to 0. How can I measure the time in even smaller unit

Hare is You Answer i think http://stackoverflow.com/questions/1861294/how-to-calculate-execution-time-of-a-code-snippet-in-c — user3269770, Feb 04 '14 at 07:28
Make the thing you measure take longer is the obvious option. If what you measure is very short you will nostly measure variability. — David Heffernan, Feb 04 '14 at 07:32

score 1 · Answer 1 · answered Feb 04 '14 at 07:30

1

The clock() will give you a resolution of 1 ms. If you want a higher resolution, use the QueryPerformanceCounter function, and QueryPerformanceFrequency

answered Feb 04 '14 at 07:30

RawBean

412
5
19

Or, the hacky way: run your code a million times :D – Brian Gradin Feb 04 '14 at 07:33

score 1 · Answer 2 · answered Feb 04 '14 at 07:57

One possible solution is to run this code segment, say for 100,000 times then calculate the average time

 double sum=0;   
    clock_t start_s=clock();

 int x = 0;

 while (x < 100000)
 {
    for(int j=1;j<size;j++)
    {
        int key=data[j];
        int i=j-1;
        while(i>=0 && data[i]>key)
        {
            data[i+1]=data[i];
            i=i-1;
        }
        data[i+1]=key;
    }      
    x++;
  }
    clock_t stop_s=clock();
    sum=((double)(stop_s - start_s)/CLOCKS_PER_SEC)/100000; //average time

score 0 · Answer 3 · answered Feb 04 '14 at 07:35

0

It looks like clock() is returning millisecond resolution ticks on Windows.

To get better granularity you should use the Windows high-resolution performance counter. Call QueryPerformanceFrequency and QueryPerformanceCounter.

answered Feb 04 '14 at 07:35

David Heffernan

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Calculate execution time of a function in c++ (visual studio 2010)

3 Answers3