How do I get milliseconds time of execution of a piece of code in Qt/C++?
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3 Answers
Use the QTime class. Start it with .start() (or .restart()) and then check the amount of milliseconds passed with .elapsed(). Naturally, the precision ultimately depends on the underlying OS, although with the major platforms you should have no trouble getting a real millisecond resolution.
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If you are running on a Windows system, then you can use timer based on the Windows Performace Timers and get microsecond timing.
Intel has a downloadable library at etimer libary. This is a small C routine that is fairly painless to use and gives very good results at the microsecond level
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If you don't use Qt you can do it with a GetTickCount:
DWORD start = ::GetTickCount(); // start counter // all the things your program does DWORD end = ::GetTickCount(); // stop counter DWORD duration = end - start; std::cout << "Duration: " << duration << " ms" << std::endl; 
3 Comments
John Dibling
GetTickCount() is useless for this kind of thing because it's accuracy is far too low. often 10-50 ms or worse. see: blogs.msdn.com/oldnewthing/archive/2005/09/02/459952.aspx
Exa
Yup, forgot to mention that. Made the same experience when using it. But is the QTime class so much more accurate? At the end, all methods depend on the OS and it's architecture, but it would be nice to know how much faster QTime is.
John Dibling
Under Windows, you can use QueryPerformanceCounter() to get high-resolution timing information. This function is not related to GetTickCount() in it's implementation.