Re: Vector vs. Array

Hi,

I think ?? Tiib is right. The code does not return anything. Therefore
the array version seems to be faster than the vector version.

This is the entire code:

#define _SECURE_SCL 0

#include "stdafx.h"
#include <iostream>
#include <ctime>
#include <cmath>
#include <vector>

using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
     vector<float> v1;
     float v2[128];
     int iterations =1000000;

     for (int i = 0; i < 128; i++)
     {
         v1.push_back(i);
         v2[i] = i;
     }

     clock_t start = clock();

     for (int i = 0; i < iterations; i++)
     {
         float sum = 0;
         for (int i = 0; i < 128; i++)
         {
             sum += fabs((v2[i])-v2[i]);
         }
     }

     clock_t end = clock();
     std::cout << "Testing time (array): " << float(end - start) /
CLOCKS_PER_SEC << " seconds" << std::endl;

     start = clock();

     for (int i = 0; i < iterations; i++)
     {
         float sum = 0;
         for (int i = 0; i < 128; i++)
         {
             sum += fabs(v1[i]-v1[i]);
         }
     }

     end = clock();
     std::cout << "Testing time (vector): " << float(end - start) /
CLOCKS_PER_SEC << " seconds" << std::endl;

     getchar();

     return 0;

}

Independent of the number of iterations, the array version returns
always 0 seconds and the vector version multiple seconds up to minutes
(in release mode).

If I add some output code like this:

#define _SECURE_SCL 0

#include "stdafx.h"
#include <iostream>
#include <ctime>
#include <cmath>
#include <vector>

using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
     vector<float> v1;
     float v2[128];
     int iterations =1000000;

     for (int i = 0; i < 128; i++)
     {
         v1.push_back(i);
         v2[i] = i;
     }

     int a = 0;

     clock_t start = clock();

     for (int i = 0; i < iterations; i++)
     {
         float sum = 0;
         for (int i = 0; i < 128; i++)
         {
             sum += fabs((v2[i])-v2[i]);
         }
         a += sum;
     }
     std::cout << a << std::endl;

     clock_t end = clock();
     std::cout << "Testing time (array): " << float(end - start) /
CLOCKS_PER_SEC << " seconds" << std::endl;

     a = 0;

     start = clock();

     for (int i = 0; i < iterations; i++)
     {
         float sum = 0;
         for (int i = 0; i < 128; i++)
         {
             sum += fabs(v1[i]-v1[i]);
         }
         a+=sum;
     }
     std::cout << a << std::endl;

     end = clock();
     std::cout << "Testing time (vector): " << float(end - start) /
CLOCKS_PER_SEC << " seconds" << std::endl;

     getchar();

     return 0;

}

Then both code versions need approx. the same time (0.6s).

Regards,

Peter

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