C++ – How to Calculate Time Difference

c++

What's the best way to calculate a time difference in C++? I'm timing the execution speed of a program, so I'm interested in milliseconds. Better yet, seconds.milliseconds..

The accepted answer works, but needs to include ctime or time.h as noted in the comments.

Best Answer

See std::clock() function.

const clock_t begin_time = clock();
// do something
std::cout << float( clock () - begin_time ) /  CLOCKS_PER_SEC;

If you want calculate execution time for self ( not for user ), it is better to do this in clock ticks ( not seconds ).

EDIT:
responsible header files - <ctime> or <time.h>

Related Solutions

C++ – Calculating Time Difference

I know this is an old question, but there's an updated answer for C++0x. There is a new header called <chrono> which contains modern time utilities. Example use:

#include <iostream>
#include <thread>
#include <chrono>

int main()
{
    typedef std::chrono::high_resolution_clock Clock;
    typedef std::chrono::milliseconds milliseconds;
    Clock::time_point t0 = Clock::now();
    std::this_thread::sleep_for(milliseconds(50));
    Clock::time_point t1 = Clock::now();
    milliseconds ms = std::chrono::duration_cast<milliseconds>(t1 - t0);
    std::cout << ms.count() << "ms\n";
}

50ms

More information can be found here:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2661.htm

There is also now a boost implementation of <chrono>.

C++ Time Calculation – Efficient Methods and Examples

Here is what I use to print time in milliseconds.

void StartTimer( _int64 *pt1 )
{
   QueryPerformanceCounter( (LARGE_INTEGER*)pt1 );
}

double StopTimer( _int64 t1 )
{
   _int64 t2, ldFreq;

   QueryPerformanceCounter( (LARGE_INTEGER*)&t2 );
   QueryPerformanceFrequency( (LARGE_INTEGER*)&ldFreq );
   return ((double)( t2 - t1 ) / (double)ldFreq) * 1000.0;
}

Use it like this:

    _int64 t1;

    StartTimer( &t1 );

    // do some stuff

    printf( "Time = %.3f\n", StopTimer( t1 ));

Best Answer

Related Solutions

C++ – Calculating Time Difference

C++ Time Calculation – Efficient Methods and Examples

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