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Top Forums UNIX for Advanced & Expert Users Doubt with fork() system call Post 302577620 by badsha6642 on Tuesday 29th of November 2011 01:13:32 PM
Old 11-29-2011
Doubt with fork() system call

Hi
I wrote a simple fork program to illustrate the fork() system cal. here it is
Code:
#include<stdio.h>
#include<sys/stat.h>
#include<sys/types.h>
main()
{
    int flag;
    flag=fork();
    if(flag==0)
    {
        printf("Child \n");    
        printf("Process id= %d\n",getpid());
        printf("Parent id= %d\n",getppid());
    }
    if(flag==-1)
        printf("Error!!!");
    else
    {
        printf("Parent\n");
        printf("Process id= %d\n",getpid());
        printf("Parent id= %d\n",getppid());
        printf("value of flag=%d\n",flag);
    }
}

i got the following output
Code:
Parent
Process id= 2332
Parent id= 1855
value of flag=2333
Child 
Process id= 2333
Parent id= 1
Parent
Process id= 2333
Parent id= 1
value of flag=0

i understood the first part i.e parent part,but how the parent id of child becomes 1?? and again how the parent process is called??

Moderator's Comments:
Mod Comment Please use code tags!

Last edited by vbe; 11-29-2011 at 02:19 PM..
 

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pthread_atfork(3T)														pthread_atfork(3T)

NAME
pthread_atfork() - register fork handlers. SYNOPSIS
PARAMETERS
prepare This function is called before performing the parent This function is called in the parent process after performing the child This function is called in the child process after performing the DESCRIPTION
The function allows an application to install fork handlers. These fork handlers will be called before and after a operation. These han- dlers will be called in the context of the thread calling Similar to the handlers, the application does not need to do anything special for these fork handlers to be called. They will be invoked by the system when a operation occurs. The function is called before the operation in the parent process. The function is called after the operation in the parent process. The function is called after the operation in the child process. If a fork handler is not needed in one or more of these three places, the appropriate fork handler parameter may be set to NULL. A process may install multiple fork handling functions. The and fork handlers will be called in the order in which they were installed (i.e., The fork handlers will be called in the opposite order (i.e., RETURN VALUE
Upon successful completion, returns zero. Otherwise, an error number is returned to indicate the error (the variable is not set). ERRORS
If any of the following occur, the function returns the corresponding error number: [ENOMEM] There is insufficient table space to install the fork handlers. AUTHOR
was derived from the IEEE POSIX P1003.1c standard. SEE ALSO
fork(2), atexit(3). STANDARDS CONFORMANCE
Pthread Library pthread_atfork(3T)
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