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Full Discussion: One parent, multiple children pipe with fork()
Top Forums UNIX for Beginners Questions & Answers One parent, multiple children pipe with fork() Post 303017883 by Ildiko on Wednesday 23rd of May 2018 07:11:54 PM
Old 05-23-2018
Linux One parent, multiple children pipe with fork()
The task I have to do is something along the lines "I receive some input and based on the first character I send it through pipe to one of the children to print".
The scheme it is based on is 1->2; 1->3; 1->4; 2 will print all the input that starts with a letter, 3 will print all the input that starts with a digit and 4 will print everything else. (Example: 12, Anne, **, *a will be printed by 3, 2, 4, 4)
I have quite understood how pipes work between one parent process and one child, but can't figure it out how to make this work, but I have tried, so I'mma attach the code down below. Any tip would be much appreciated.
Code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{ int pipefd[2];
  int pipefe[2];
  int pipeff[2];
  pipe(pipefd);
  pipe(pipefe);
  pipe(pipeff);

  char arr[80];
  scanf("%s", arr);
  int f1 = fork();
  
  if(f1>0)
	{close(pipefd[0]);
	 close(pipefe[0]);
	 close(pipeff[0]);
	 if (arr[0]>='A'&&arr[0]<='z')
		{
         	write(pipefd[1], arr, strlen(arr)+1);
	 	close(pipefd[1]);
		}
	if(arr[0]>='0' && arr[0]<='9')
		{
		write(pipefe[1], arr, strlen(arr)+1);
	 	close(pipefe[1]);
		}
	else
	   {
	    write(pipeff[1], arr, strlen(arr)+1);
	    close(pipeff[1]);
	   }
         exit(0);
	}
   else if(fork()==0)
     { wait(NULL);
       close(pipefd[1]);
       read(pipefd[0], arr, strlen(arr)+1);
       printf("%s\n", arr);
       close(pipefd[0]);
       exit(0);
     }
   else if(fork()==0)
     { wait(NULL);
       close(pipefe[1]);
       read(pipefe[0], arr, strlen(arr)+1);
       printf("%s\n", arr);
       close(pipefe[0]);
       exit(0);
     }
   else if(fork()==0)
     { wait(NULL);
       close(pipeff[1]);
       read(pipeff[0], arr, strlen(arr)+1);
       printf("%s\n", arr);
       exit(0);
       return 0;
     }

}

 

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LEARN ABOUT SUSE

xquerytree

XQueryTree(3)							  XLIB FUNCTIONS						     XQueryTree(3)

NAME

       XQueryTree - query window tree information

SYNTAX

       Status XQueryTree(Display *display, Window w, Window *root_return, Window *parent_return, Window **children_return, unsigned int *nchil-
	      dren_return);

ARGUMENTS

       children_return
		 Returns the list of children.

       display	 Specifies the connection to the X server.

       nchildren_return
		 Returns the number of children.

       parent_return
		 Returns the parent window.

       root_return
		 Returns the root window.

       w	 Specifies the window whose list of children, root, parent, and number of children you want to obtain.

DESCRIPTION

       The XQueryTree function returns the root ID, the parent window ID, a pointer to the list of children windows (NULL when there are no chil-
       dren), and the number of children in the list for the specified window.	The children are listed in current stacking order, from bottom-
       most (first) to top-most (last).  XQueryTree returns zero if it fails and nonzero if it succeeds.  To free a non-NULL children list when it
       is no longer needed, use XFree.

       XQueryTree can generate a BadWindow error.

BUGS

       This really should return a screen *, not a root window ID.

DIAGNOSTICS

       BadWindow A value for a Window argument does not name a defined Window.

SEE ALSO

       XFree(3), XGetWindowAttributes(3), XQueryPointer(3)
       Xlib - C Language X Interface

X Version 11							   libX11 1.3.2 						     XQueryTree(3)
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