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Full Discussion: fork function
Top Forums UNIX for Dummies Questions & Answers fork function Post 46829 by a25khan on Tuesday 27th of January 2004 04:54:45 PM
Old 01-27-2004
Error fork function
hi everyone,
have this little piece of code in order to help you understand my question
Code:
#include<stdio.h>
#include<unistd.h>

int main()
{
	int i, pid;
	pid = fork();

	if(pid<0)
	{
		fprintf(stderr, "fork failed\n");
		_exit(1);
	}
	if(pid==0)
	{
		printf("in Child\n");
		_exit(0);
	}
	printf("in parent\n");
}

/** my question is: according to the definition of fork, it creates an
exact copy of original process. what is the original process here?
is it the whole code i.e. the program where this code is written
i named it as one.c, so is one.c the original process? orrrr
when i do pid = fork(), thats the original process created in one.c?
also does the child process exists only in the if loops if child
succeeds?
about fork() function, how does it generates a number? is it like
generating a random number? i just can't figure out, whats my parent process here and whats my child process here, i m confused with the two.
if fork is created when i do pid = fork(), isn't that the
parent process created? and in order to create a child process
am i not supposed to do pid = fork() again!? and what do the parent and child process share in common and what are their differences. i m aware that fork is done for synchronization but m having trouble with the basic */
appreciate your comments.

code tags added for readability --oombera
Last edited by oombera; 04-12-2004 at 01:18 AM..
 

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LEARN ABOUT LINUX

pid

pid(n)                                                         Tcl Built-In Commands                                                        pid(n)

__________________________________________________________________________________________________________________________________________________

NAME

       pid - Retrieve process identifiers

SYNOPSIS

       pid ?fileId?
_________________________________________________________________

DESCRIPTION

       If  the  fileId  argument is given then it should normally refer to a process pipeline created with the open command.  In this case the pid
       command will return a list whose elements are the process identifiers of all the processes in the pipeline, in order.   The  list  will  be
       empty if fileId refers to an open file that is not a process pipeline.  If no fileId argument is given then pid returns the process identi-
       fier of the current process.  All process identifiers are returned as decimal strings.

EXAMPLE

       Print process information about the processes in a pipeline using the SysV ps program before reading the output of that pipeline:

              set pipeline [open "| zcat somefile.gz | grep foobar | sort -u"]
              # Print process information
              exec ps -fp [pid $pipeline] >@stdout
              # Print a separator and then the output of the pipeline
              puts [string repeat - 70]
              puts [read $pipeline]
              close $pipeline

SEE ALSO

       exec(n), open(n)

KEYWORDS

       file, pipeline, process identifier

Tcl                                                                     7.0                                                                 pid(n)
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