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clock() returning 0 on Linux

Started by TheMightyDude Jun 10, 2006 at 7:58 PM 8 replies 3.2k views

Original Post

Jun 10, 2006 at 7:58 PM

Hello All I have a cpp file which is suppose to display a two clock ticks values but it just returns 0 on both. And time() isnt any good due to I need values that update in ms and not in seconds. This is a very basic bit of code:


#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>

int main (int argc, char **argv)
{
    clock_t start,stop;
    start = clock();
    printf("start: %d\n",(int)start);
    sleep(1);
    stop = clock();
    printf("stop: %d\n",(int)stop);
    return 0;
}

Anyone know why it's doing this? This worked on my old Linux box fine, but not on this one.

Null and Void

163

Null and Void

Jun 10, 2006 at 8:02 PM

Not that this actually answers your question, but have you tried an alternative method of time request?

See: What functions are recommended for high precision time retrieval?.

It's worth a shot to see what happens, right? :)

TheMightyDude

Author

TheMightyDude

Jun 10, 2006 at 9:27 PM

Quote:
Original post by Null and Void
Not that this actually answers your question, but have you tried an alternative method of time request?

See: What functions are recommended for high precision time retrieval?.

It's worth a shot to see what happens, right? :)

Yup, I had to do some minor code changes but that clock_gettime() worked fine.

Thanks

Paul Kirby

joanusdmentia

Jun 10, 2006 at 9:30 PM

Try this and see if it makes a difference:

int main (int argc, char **argv){    clock_t start,stop;    start = clock();    printf("start: %llu\n",(unsigned long long)start);    sleep(1);    stop = clock();    printf("stop: %llu\n",(unsigned long long)stop);    return 0;}

TheMightyDude

Author

TheMightyDude

Jun 10, 2006 at 9:34 PM

Quote:
Original post by joanusdmentia
Try this and see if it makes a difference:

*** Source Snippet Removed ***

Nope returned the following:

start: 0stop: 0

Evil Steve

382

Evil Steve

Jun 11, 2006 at 4:51 AM

Red Hat by any chance? I had this too. I never found a solution unfortunately...

kinetik_mjg

Jun 11, 2006 at 6:18 AM

clock(3) returns processor time, not wall-clock time. If your test did something useful rather than sleeping, your second call to clock(3) would yield a value greater than zero.

#include <stdio.h>#include <time.h>int main(int argc, char *argv[]){  int i;  for (i = 0; i < 10000000; ++i)    ;  printf("took: %fs CPU time\n", (double) clock() / CLOCKS_PER_SEC);  return 0;}

If you want high precision timers for wall-clock time, take a look at gettimeofday(2) or clock_gettime(2).

Shadowdancer

Jun 11, 2006 at 6:23 AM

Quote:

If you want high precision timers for wall-clock time, take a look at gettimeofday(2) or clock_gettime(2).

And make sure to read the manpages all the way, there's interesting stuff about the usefulness of those functions.

TheMightyDude

Author

TheMightyDude

Jun 11, 2006 at 9:20 AM

Thanks for all the helpfull replies :)
I think I will go with Null and Void's idea.

Thanks
Paul kirby

abdulla

Jun 12, 2006 at 9:31 AM

Also note that OS X doesn't (as of 10.4) have support for clock_gettime. In case you plan on being more portable.

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