Question

I wanted to know the execution time of a program, but I also wanted to exclude the time needed for file input/output. For this purpose I used the time() function. There are many .h and .cpp files but here are the only places where time objects are referenced.

My problem is, while start’s value is set correctly at the beginning it loses it (is set to zero) when dosomethingelse() is invoked for the first time. This makes sub_duration to have a very big value because now the difference between end and start , which is zero, is the value of end.

Here is how I used it:

main.cpp

time_t start=0;
time_t end=0;
time_t sub_duration=0;
time_t total_duration=0; 

int main()
{
    start = time(NULL);
    while(somethingtodo)
    {
        dosomething();
        dosomethingelse();
    }
    end = time(NULL);
    sub_duration = difftime(end,start);
    total_duration += sub_duration;
}

dosth.h

   extern      time_t start;
   extern      time_t end;
   extern      time_t sub_duration;
   extern      time_t total_duration;
   dosomethingelse();

dosth.cpp

#include"dosth.h"    
dosomethingelse()
{
    if(somecondition)
    {
        end = time(NULL);
        sub_duration = difftime(end,start);
        total_duration += sub_duration;
        writesomethingTofile();
        start = time(NULL);
    }
}

Answer 1

The problem is that start and end are global… when you set them inside dosomethingelse(), you’re re-setting the start for the whole program.

The solution is to keep a local timer inside dosomethingelse(), and subtract the time spent in that function from the total.