fork() help...beginner!!!

[spelbound]

Hi I'm in the very early stages of my OS course...We are fresh on the topic of the fork(). So, the if statement code:

// if((childpid = fork()) == 0)

does what?

As a guess, it creates childpid and checks to see if it is a child...

[michaelb]

The fork system call creates a child process.
After that you typically have some code that executes in the child process, and some code that executes in the parent process.
The value returned from the fork is used to determine where you are.
Here's a little illustration

 
   int pid;
   pid = fork();
 
   if (pid == 0)
   {
      /* 
      ** fork() returned 0, meaning we are in
      ** the child process. So put your "child" code 
      ** in this section.
      */
   }
   else if (pid > 0)
   { 
       /* 
       ** Continue with the Parent process;
       ** the same process that executed the fork() call.
       ** You may have more code in this section.
       */
   }
   else
   {   
      /*
      ** return value is negative, meaning that
      ** fork() failed. Typically you would have 
      ** some error-handling here.
      */
   }
 
 

[Motoma]

Great example MichaelB! Thanks!