Tuesday, 17 February 2015

Calculate elapsed time - C Programming

Welcome to Logically Proven Blog.

This post teaches you how to measure the time taken by a function or a set of statements or a complete program.

It is very important to track the performance of our own application in certain cases where the execution time of a program plays a major role.

To calculate time taken by a process, we use clock() function which is available in a system library time.h. We can make use of available function in this library to calculate the elapsed time of a program.

For example,we want to calculate the execution time of a program, we can call the clock functions at the beginning and at the end of the code for which we measure time, subtract the values, and then divide by CLOCKS_PER_SEC (the number of clock ticks per second) to get processor time.

Syntax:

#include <time.h>
 
clock_t start, end;
double elapsed_used;
 
start = clock();
... /* Do your work. */
end = clock();
elapsed_used = ((double)(end - start)) / CLOCKS_PER_SEC;

Example:

#include <stdio.h>
#include <time.h>
 
// A function that terminates when enter key is pressed
void funElapsedTime()
{
 printf("START \n");
 printf("Press enter to stop \n");
 while (1)
 {
  if (getchar())
   break;
 }
 printf("END \n");
}
 
// The main program calls function and calculates the elapsed time
int main()
{
 clock_t start,end;
 start = clock();
 funElapsedTime();
 end = clock();
 //calculate elapsed time
 double elapsed_time = ((double)(end-start)) / CLOCKS_PER_SEC; // in seconds
 
 printf("funElapsedTime took %f seconds to execute \n", elapsed_time);
 return 0;
}
 
 
/*output: START
          Press enter to stop
 
          END
   funElapsedTime took 5.010000 seconds to execute */

So you can include these clock functions anywhere in the program that you want to calculate the elapsed time.

Ref: http://www.gnu.org/software/libc/manual/html_node/CPU-Time.html

Please write your comments if you find anything is incorrect or do you want to share more information about the topic discussed above.

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