I have a C program that aims to be run in parallel on several processors. I need to be able to record the execution time (which could be anywhere from 1 second to several minutes). I have searched for answers, but they all seem to suggest using the
CLOCKS_PER_SEC is a constant which is declared in
<time.h>. To get the CPU time used by a task within a C application, use:
clock_t begin = clock(); /* here, do your time-consuming job */ clock_t end = clock(); double time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
Note that this returns the time as a floating point type. This can be more precise than a second (e.g. you measure 4.52 seconds). Precision depends on the architecture; on modern systems you easily get 10ms or lower, but on older Windows machines (from the Win98 era) it was closer to 60ms.
clock() is standard C; it works "everywhere". There are system-specific functions, such as
getrusage() on Unix-like systems.
System.currentTimeMillis() does not measure the same thing. It is a "wall clock": it can help you measure how much time it took for the program to execute, but it does not tell you how much CPU time was used. On a multitasking systems (i.e. all of them), these can be widely different.