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7.4

Two way piped process

Asked by k7t266 in Programming Languages, Shell Scripting

Tags: dup2, execlp, pipe

Hi,

I have some problems with my program. I need to run a program from another(i'm using fork and execlp). I need to redireting standart input and output of the child cause i can't modify it. I can modify the input or the output with a dup2 on a file descriptor created by pipe(). But i cant modify the input and the output in the same time: the program is blocked. I'm using two file descriptor: one for parent->child and the other for child->parent. First i write a number to the child who "scanf" it and after it returns me the double by a printf that i read in the parent.

Here the code(its a trying program):

#include <stdio.h>
#include <stdlib.h>

int
main (void)
{int fd[2],fd2[2];
 int pid;    
 char buff[5];
 pipe(fd);
 pipe(fd2);
 pid=fork();
 strcpy(buff,"     ");
 if(pid==0)
      {dup2(fd2[1],1);
      dup2(fd[0],0);
      close(fd[1]);
      close(fd2[0]);
      execlp("enfant","enfant",0);}
 else
      {close(fd2[1]);
      close(fd[0]);
      write(fd[1],"12",2);
      read(fd2[0],buff,5);
      printf("s:%s\n",buff);
         }      
}

enfant:

#include<stdio.h>

int main(void){long i;
     char buff[9];
     scanf("%s",buff);
     buff[8]='\0';
     i=atol(buff)*2;
     printf("c:%d\n ",i);
     }
Please gimme an answer i need this to succeed in my year im a student!
 
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[+][-]11/25/02 10:41 AM, ID: 7495191Accepted Solution

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About this solution

Zones: Programming Languages, Shell Scripting
Tags: dup2, execlp, pipe
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Solution Provided By: zebada
Participating Experts: 3
Solution Grade: A
 
[+][-]11/25/02 10:31 AM, ID: 7495142Expert Comment

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[+][-]11/26/02 12:23 PM, ID: 7500168Expert Comment

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[+][-]03/30/04 09:53 AM, ID: 10715745Administrative Comment

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