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clock() not working

Posted on 2002-03-06
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#include <time.h>

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

output: cpu= 0
0
Question by:anothercto
• 6
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LVL 86

Expert Comment

printf("cpu= %f",((double) clock())/CLOCKS_PER_SEC);
0

LVL 86

Expert Comment

FYI, the way you did it, you're doing an integer division. So, if clock() < CLOCKS_PER_SEC, the result is '0'...
0

Author Comment

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..
0

LVL 1

Expert Comment

clock()/CLOCKS_PER_SEC just shows how long your your app has been running in seconds
0

LVL 1

Expert Comment

clock()/CLOCKS_PER_SEC just shows how long your your app has been running in seconds
0

LVL 1

Expert Comment

so 0 means the application executed really  fast
through  a  in a 6000000 empty loops in your app and see how long it  take
0

Author Comment

and most of the times my program takes 0 micro seconds to run? (sometimes 1500 micro seconds.)
0

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Accepted Solution

so 0 means the application executed really  fast
through  a  in a 6000000 empty loops in your app and see how long it  take
0

LVL 1

Expert Comment

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
0

LVL 1

Expert Comment

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);

}
0

Expert Comment

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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