Timing Your Application

How fast your application executes is one indication of performance. When timing the speed of applications, consider the following circumstances:

Run program timings when other users are not active. Your timing results can be affected by one or more CPU-intensive processes also running while doing your timings.
Try to run the program under the same conditions each time to provide the most accurate results, especially when comparing execution times of a previous version of the same program. Use the same system (processor model, amount of memory, version of the operating system, and so on) if possible.
If you do need to change systems, you should measure the time using the same version of the program on both systems, so you know each system's effect on your timings.
For programs that run for less than a few seconds, run several timings to ensure that the results are not misleading. Certain overhead functions, like loading external programs, might influence short timings considerably.
If your program displays a lot of text, consider redirecting the output from the program. Redirecting output from the program will change the times reported because of reduced screen I/O.

The following program illustrates a model for program timing:

/* Sample Timing */

#include <stdio.h>

#include <stdlib.h>

#include <time.h>

int main(void)

{

clock_t start, finish;

long loop;

double duration, loop_calc;

start = clock();

for(loop=0; loop <= 2000; loop++)

{

loop_calc = 123.456 * 789;

//printf() inculded to facilitate example

printf("\nThe value of loop is: %d", loop);

}

finish = clock();

duration = (double)(finish - start)/CLOCKS_PER_SEC;

printf("\n%2.3f seconds\n", duration);

}