io related question, when printf is called

blackzone · 07-26-2004, 04:52 AM

I sometimes got printf() called at unexpected time.
For example for the program below I would expect output of "0" wait 5 second than a "1"

But I got wait 5 second and "01" print at the same time.

Can give more insite of why this happened? Believe it have something to do with buffer?

---------------------------------------------------------------------------------------
int main(){
int i=0;
printf("%d", i);

sleep(5)

i++;
printf("%d, i);
}

Vookimedlo · 07-26-2004, 05:37 AM

It's normal, standard output is buffered, but standard error output isn't.

For error outputs use stderr streams.

But if you want to use normal output, you should always invoke fflush(FILE*)

for example:

Code:

#include <stdio.h>

int main (int argc, char **argv)
{
  int i=0;
  printf("%d", i);
  fflush(stdout);

  sleep(5);    
  i++;
  printf("%d", i);

  return 0;
}

Mohsen · 07-26-2004, 05:41 AM

use this one instead:

Code:

int main(){
  int i=0;
  printf("%d", i);
  fflush (stdout); // force output buffer to be displayed!
  sleep(5);
  i++;
  printf("%d, i);
}