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Full Discussion: A small question about fork()
Top Forums Programming A small question about fork() Post 302224333 by mlhazan on Wednesday 13th of August 2008 01:19:21 AM
Old 08-13-2008
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$

 

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LEARN ABOUT SUNOS

getpid

getpid(2)							   System Calls 							 getpid(2)

NAME

       getpid, getpgrp, getppid, getpgid - get process, process group, and parent process IDs

SYNOPSIS

       #include <unistd.h>

       pid_t getpid(void);

       pid_t getpgrp(void);

       pid_t getppid(void);

       pid_t getpgid(pid_t pid);

DESCRIPTION

       The getpid() function returns the process ID of the calling process.

       The getpgrp() function returns the process group ID of the calling process.

       The getppid() function returns the parent process ID of the calling process.

       The getpgid() function returns the process group ID of the process whose process ID is equal to pid, or the process group ID of the calling
       process, if pid is equal to 0.

RETURN VALUES

       Upon successful completion, these functions return the process group ID. Otherwise, getpgid() returns (pid_t)-1 and sets errno to  indicate
       the error.

ERRORS

       The getpgid() function will fail if:

       EPERM	       The  process  whose  process   ID is equal to pid is not in the same session as the calling process, and the implementation
		       does not allow access to the process group ID of that process from the calling process.

       ESRCH	       There is no process with a process ID equal to pid.

       The getpgid() function may fail if:

       EINVAL	       The value of the pid argument is invalid.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       intro(2), exec(2), fork(2), getsid(2), setpgid(2), setpgrp(2), setsid(2), signal(3C), attributes(5), standards(5)

SunOS 5.10							    28 Dec 1996 							 getpid(2)
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