Keeping pids

This is a discussion on Keeping pids within the C Programming forums, part of the General Programming Boards category; As I fork() 2 childs from the same parent, I would like to keep my first child's pid and pass ...

  1. #1
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    Keeping pids

    As I fork() 2 childs from the same parent, I would like to keep my first child's pid and pass it to the 2nd child. Question is how do I do it? I've tried global variables or maybe I did it incorrectly.

    From the start, I was told by my lecturer that global variables are bad so I didn't read much about it. Here's a piece of the code...

    Code:
    #include <sys/types.h>
    #include <sys/wait.h>
    #include <unistd.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <fcntl.h>
    #include <stdio.h>
    #include <signal.h>
    #include <errno.h>
    
    int firstID;
    
    int main(){
    
      int id;
    
      if(fork() == 0){
        id = (int)getpid();
        printf("I am child : %d\n", id);
        firstID = id;
      }
      else{
        if(fork() == 0){
          printf("My First child's ID : %d\n", firstID);
        }
      }
    
      return 0;
    }
    When I print the pid on the 2nd fork, it shows me '0'.

  2. #2
    ATH0 quzah's Avatar
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    Global variables are initialized to zero by default.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    But if you see the code there, in the first fork, I've set the variable with the pid but it didn't appear on the second fork.

    Is there any solution on how I can keep the value of the first child's pid so it can be printed in the second child?

  4. #4
    and the hat of wrongness Salem's Avatar
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    Code:
    int main(){
      int id;
    
      id = fork();
      if(id == 0){
        id = (int)getpid();
        printf("I am child : %d\n", id);
      }
      else{
        if(fork() == 0){
          printf("My First child's ID : %d\n", id);
        }
      }
    
      return 0;
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  5. #5
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    Quote Originally Posted by quzah
    Global variables are initialized to zero by default.


    Quzah.
    I thought that was only if the 'static' keyword was present.

  6. #6
    Just Lurking Dave_Sinkula's Avatar
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    Nope.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  7. #7
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    Thanks Salem, I got it to work this time

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