/*
 * This program demonstrates how to calculate the actual
 * processing time of a part of your program, say the 
 * execution time of function f(). The program uses the 
 * function clock(), the clock_t type, and the constant
 * CLOCKS_PER_SEC defined in the C++ standard library "ctime".
 *
 *	Note: You can also use C's gettimeofday() function for timing, instead of this.
 */
 
// be sure to include <ctime>
#include<ctime>
#include<iostream>
using namespace std;
int main(int argc,char *argv[]) {

  /*
   * We use the clock() program in library <ctime>. Program clock()
   * returns the number of clock ticks elapsed since the process 
   * starts. The number of clock ticks is represented by type clock_t.
   *
   * If you wonder why we don't use time(), it's because time() 
   * returns a value with a precision only to seconds.
   */
   
  /* record the number of elapsed ticks before calling f() */
  clock_t start=clock();

  // ---> call f() here <---

  /* record the number of elapsed ticks after calling f() */
  clock_t end=clock();
  
  /*
   * The number of ticks elapsed during the f() function call 
   * can be calculated by (end - start). The constant 
   * CLOCKS_PER_SEC specifies the relation between a clock tick
   * and a second (i.e. clock ticks per second). Therefore, dividing
   * (end - start) by CLOCKS_PER_SEC will give you the elapsed
   * time in seconds.
   */
  cout << "CPU elapsed time in seconds: "
       <<(double)(end - start)/CLOCKS_PER_SEC <<endl;


       
  return 0;
}

/* A way to improve the precision of measurement is to start
 * timing right after the clock ticks and also measure for many
 * times and get the average value.

    // Wait for the clock to tick and record the start time
    clock_t k = clock();
    clock_t start;
    do start = clock();
    while (start == k);
    
    // ---> call f() here <---
    
    clock_t end=clock();
    
    cout << "CPU elapsed time in seconds: "
         <<(double)(end - start)/CLOCKS_PER_SEC <<endl;
    
 * Reference: 
 * A program described in	B. Stroustrup: Wrapping C++ Member Function Calls
 * "The C++ Report" June 2000
 * http://www.research.att.com/~bs/wrap_code.cpp
 */