Question

I’m doing some prototyping work in C, and I want to compare how long a program takes to complete with various small modifications.

I’ve been using clock; from K&R:

clock returns the processor time used by the program since the beginning of execution, or -1 if unavailable.

This seems sensible to me, and has been giving results which broadly match my expectations. But is there something better to use to see what modifications improve/worsen the efficiency of my code?

Update: I’m interested in both Windows and Linux here; something that works on both would be ideal.

Update 2: I’m less interested in profiling a complex problem than total run time/clock cycles used for a simple program from start to finish—I already know which parts of my program are slow. clock appears to fit this bill, but I don’t know how vulnerable it is to, for example, other processes running in the background and chewing up processor time.

Answer 1

In POSIX (e.g. on Linux), you can use gettimeofday() to get higher-precision timing values (microseconds).

In Win32, QueryPerformanceCounter() is popular.

Beware of CPU clock-changing effects, if your CPU decides to clock down during the test, results may be skewed.