Timing a program

[dietao234]

I have found that often I am asking which way of solving problems are faster. Thus I will ask how to time a program here so that I can test the runspeed myself. In Java I know you can use

long start = System.currentTimeMillis();

and then to display how much time you can do System.out.println(System.currentTimeMillis()-start);

How would you do this in C++?

Thanks in advance.

[Lindley]

There are a number of approaches. The simplest is to call clock() or time(), and compare the results, possibly using difftime().

However, that will only get you accuracy to about 10ms or so, and for many things that isn't good enough.

On Windows, QueryPerformanceCounter() is a good option. On Unix-based systems, gettimeofday() provides similar accuracy.

However, the most useful approach is profiling the code as a whole, which actually doesn't involve modifying the code at all. Not sure about Windows, but on Unix-based systems, compile with the -pg flag, then run the program to completion, and then pass the dumped gmon.out file to gprof for the analysis.

[Martin O]

This CodeGuru faq might help:

C++ Profiling: How do I determine the speed of a particular function or operation?