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    <p>It's mind-bending at first, but you seem to grasp that, when you call fork( ): </p> <ul> <li><p>the calling process (the "parent") is essentially duplicated by the operating system and the duplicate process becomes the "child" with a unique PID all its own;</p></li> <li><p>the returned value from the fork( ) call is either: integer 0,<sup>1</sup> meaning that the program receiving the 0 return is the "child"; or it is the non-zero integer PID of that forked child; and </p></li> <li><p>the new child process is entered into the scheduling queue for execution. The parent remains in the scheduling queue and continues to execute as before.</p></li> </ul> <p>It is this ( 0 <strong>.xor.</strong> non-0 ) return from fork( ) that tells the program which role it's playing at this instant -- 0 returned, program is the child process; anything else returned, program is the parent process.</p> <p>If the program playing the parent role wants many children, he has to fork( ) each one separately; there's no such thing as multiple children sharing a fork( ).</p> <p>Intermediate results certainly can be sent via a pipe.</p> <p>As for calling each child with different parameters, there's really nothing special to do: you can be sure that, when the child gets control, he will have (copies of) exactly the same variables as does the parent. So communicating parameters to the child is a matter of the parent's setting up variable values he wants the child to operate on; and then calling fork( ).</p> <hr> <p><sup>1</sup> More accurately: fork( ) returns a value of type <code>pid_t</code>, which these days is identical to an integer on quite a few systems.</p>
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    1. POfork and exec many different processes, and obtain results from each one
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    1. COMost examples I've seen so far and the one I'm using, establish a single fork and process. Do multiple children & processes get assigned different PID's ? The examples I've seen use PID zero for the child, and non zero for the parent. What I need is a way to establish which is child is which process to relate to output. Basically I need 8 processes easily distinguishable from one another. Any help on that please?
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    2. CO@Alex -- yes, each forked child get its own unique PID which is returned to the program that called fork( ). The call to fork( ) that returns **in the child** returns the value zero -- that's how the child knows it's the child. The child then has to issue **getpid( )** to find out its own process ID. That PID -- the one returned to the child by getpid( ) -- is the same one that was returned to the parent from the fork( ) call that started the child.
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    3. COThanx, I didn't see this reply! This should help me figure out, thank you for your help.
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