Thread: printf() or write(1,...) when using fork?

I am not sure which print function to use after fork() system call. Should I use printf(), or sprintf with write to stdout?

I was googling a lot about it. and some people say use one, some people say use another.

Any help is appreciated, thanks.

So, if printf is used concurrently, both from child and parent, interleaving will not occur?

Example of interleaving I am thinking of:
parent: printf("Hello");
child: printf("World\n");
output to console: HeWollorld

Thanks for your help

The main issue with printf() on either side of a fork() is that standard I/O is buffered. Something like:

Code:

#include <stdio.h>
#include <unistd.h>

int main(void)
{
  printf("Hello");

  if(fork() == 0)
  {
    puts("child");
    _exit(0);
  }

  puts("parent");

  return 0;
}

Could easily produce output like:

Code:

Helloparent
Hellochild

This is the case if "Hello" is put in the buffer but not flushed (which it probably will be since there has been no newline printed); thus the child and parent both have a buffer with "Hello", and when the flush happens, they both print it. This wouldn't be the case with write(), but you'd also be OK if you just did fflush(NULL) (this flushes all output streams; you can choose just one if that's all you're using) before the fork().

I understand now.
Thanks for your help guys, I appreciate it.