Execution time of C program

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.

Java's 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.

If you are using the Unix shell for running, you can use the time command.

doing

$ time ./a.out

assuming a.out as the executable will give u the time taken to run this

In plain vanilla C:

#include <time.h>#include <stdio.h>int main(){    clock_t tic = clock();    my_expensive_function_which_can_spawn_threads();    clock_t toc = clock();    printf("Elapsed: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);    return 0;}