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clock() not working

Posted on 2002-03-06
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Last Modified: 2010-05-18
#include <time.h>

....
printf("cpu= %g",clock()/CLOCKS_PER_SEC);
.....

output: cpu= 0
0
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Question by:anothercto
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by:jkr
ID: 6844971
Make it read

printf("cpu= %f",((double) clock())/CLOCKS_PER_SEC);
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by:jkr
ID: 6844977
FYI, the way you did it, you're doing an integer division. So, if clock() < CLOCKS_PER_SEC, the result is '0'...
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by:anothercto
ID: 6845006
actually I did use the 'double' cast. what really happens is that when I run the program, one out of 4 times, I get cpu=0.015, I get cpu= 0 the other 3 times..
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by:madface
ID: 6845007
clock()/CLOCKS_PER_SEC just shows how long your your app has been running in seconds
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by:madface
ID: 6845010
clock()/CLOCKS_PER_SEC just shows how long your your app has been running in seconds
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by:madface
ID: 6845023
so 0 means the application executed really  fast
through  a  in a 6000000 empty loops in your app and see how long it  take
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Author Comment

by:anothercto
ID: 6845034
and most of the times my program takes 0 micro seconds to run? (sometimes 1500 micro seconds.)
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madface earned 50 total points
ID: 6845046
so 0 means the application executed really  fast
through  a  in a 6000000 empty loops in your app and see how long it  take
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by:madface
ID: 6845078
the best way to show you is to break in to the debugger.
wait a while
and execute  the printf statement
it should be a larger number



clock() returns how many ticks  have  elapsed  since you  started  the  app

CLOCKS_PER_SECOND is how many ticks there are in a sec

you get  it
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by:madface
ID: 6845102
try this  code


void
main()
     {

     long i = 0;

     while(i < 60000000)
          {
          i++;
          }
     
     float cl = clock();
     float val = cl/CLOCKS_PER_SEC;
     printf("cpu= %f",val);

     }
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Expert Comment

by:dchan_4544
ID: 6845175
Actually, clock() reports CPU time USED, which means how much CPU your program actually uses.  So, if your program is not doing much at all, the number you'll get from clock()/CLOCKS_PER_SEC will be very small (very close to 0).  To see a difference, you may be able to do something more complex in a loop like doing bunch of if's or something.  Good luck.

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