problem with time function

**Thegame16** · 09-27-2011

Hey guys i am doing a basic swap program with generic pointers and I am trying to time it but I keep getting 0. Any idea why?

Code:



 #include <iostream>
 #include <iomanip>
#include <ctime>
 using namespace std;

 void q(void *a, void *b, int n) {

clock_t c0, c1;

unsigned char *ca = (unsigned char *)a;
unsigned char *cb = (unsigned char *)b;
unsigned char c;

c0 = clock();


     for (int i = 0; i < n; i++) {
         c     = ca[i];
         ca[i] = cb[i];
         cb[i] = c;
     }

c1 = clock();

cout << "Process time is " <<
      (double)(c1-c0)/CLOCKS_PER_SEC
      << " secs" << endl;



 }

 int main() {

     int a = 4, b = 7;
     float x = 2.5f, y = 3.5f;

     q(&a, &b, sizeof(int));
     q(&x, &y, sizeof(float));

     cout << setprecision(1) << fixed;
     cout << "(a,b) = (" << a << ',' << b << ')' << endl;
     cout << "(x,y) = (" << x << ',' << y << ')' << endl; 
 }

**laserlight** · 09-27-2011

Probably because what you are timing completes faster than the resolution of the timer

By the way, you should indent your code better

**Thegame16** · 09-27-2011

is there anything i can change so i can get a time?

**Salem** · 09-27-2011

Well if you're on windows, then read QueryPerformanceCounter function (Windows)
Or state what machine/OS/Compiler you're using.

**ushacy** · 09-28-2011

hey make your process to take more time for eg. put some sleep(2000) in for loop then you will get the time as 1.99999 like this...

**AndrewHunter** · 09-28-2011

Originally Posted by ushacy

hey make your process to take more time for eg. put some sleep(2000) in for loop then you will get the time as 1.99999 like this...

Doesn't really solve his problem as the OP was looking to check how long it took for his sort to work.

**Elysia** · 09-28-2011

Another good idea might to run the algorithm for X iterations and time it. Then divide your time with the number of iterations and voila - you get a result. An average even, which is better statistically than a single iteration.

**Thegame16** · 09-28-2011

basically what I want to do is take that swap function and make it happen 1000 times. I believe if I do that I should get a time value. I tried replacing n with 1000 but then it would just mess up the swap all together, so I have to keep sizeof.

Is there anyway I could make the swap happen 1000 times while still using the sizeof I am sending in?

**Salem** · 09-28-2011

Where did 1000 come from?

Elysia suggested this

Code:

- clock
-- for ( i = 0 ; i < 100000 ; i++ )
--- q(&a, &b, sizeof(int));
-- end for
- clock
- print time for 1M swaps of an int

Move the clock code from the function under test and put it in main.

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