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Top Forums Programming A small question about fork() Post 302224333 by mlhazan on Wednesday 13th of August 2008 01:19:21 AM

08-13-2008

Registered User

A small question about fork()

Hello experts,
I am using fork() in my code but I am confused which output comes first child or parent?
I did the following code .My book shows parent first but my linux shows child first.Can anyone tell me why?

Code:

#include <stdio.h>
int main(){
int pid;
printf("I am original process with pid is %d ,My parent (Terminal) pid is %d\n",getpid(),getppid());
pid=fork();
if(pid>0)//parent starts
    {
    printf("I am parent,my pid is %d and my parent pid is %d\n",getpid(),getppid());
    }
else 
    {
    printf("I am child,my pid is %d and my parent pid is %d\n",getpid(),getppid());
    }
//both parent and child executes the next printf
printf("PID %d terminates \n",getpid());    
}

output:

Code:

mlhazan@dEBx:~/Desktop$ gcc myFork.c 
mlhazan@dEBx:~/Desktop$ ./a.out 
I am original process with pid is 13426 ,My parent (Terminal) pid is 28555
I am child,my pid is 13427 and my parent pid is 13426
PID 13427 terminates 
I am parent,my pid is 13426 and my parent pid is 28555
PID 13426 terminates 
mlhazan@dEBx:~/Desktop$

mlhazan

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LEARN ABOUT PHP

pcntl_fork

PCNTL_FORK(3)								 1							     PCNTL_FORK(3)

pcntl_fork - Forks the currently running process

SYNOPSIS

       int pcntl_fork (void  )

DESCRIPTION

	The pcntl_fork(3) function creates a child process that differs from the parent process only in its PID and PPID. Please see your system's
       fork(2) man page for specific details as to how fork works on your system.

RETURN VALUES

	On success, the PID of the child process is returned in the parent's thread of execution, and a 0 is returned in  the  child's	thread	of
       execution. On failure, a -1 will be returned in the parent's context, no child process will be created, and a PHP error is raised.

EXAMPLES

       Example #1

	      pcntl_fork(3) example

	      <?php

	      $pid = pcntl_fork();
	      if ($pid == -1) {
		   die('could not fork');
	      } else if ($pid) {
		   // we are the parent
		   pcntl_wait($status); //Protect against Zombie children
	      } else {
		   // we are the child
	      }

	      ?>

SEE ALSO

       pcntl_waitpid(3), pcntl_signal(3), setproctitle(3).

PHP Documentation Group 													     PCNTL_FORK(3)

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