two way communication between child and parent processes in C using pipes

Question

0.00/5 (No votes)

See more:

I want parent and child processes to communicate in C linux using pipes. I have created two file descriptors. one for parent to child i.e. readpipe and other writepipe for viceversa.
But I am getting null as output for ch and ch1 strings in my code below.
Please help me in this.

C++

#include <stdio.h>
#include<stdlib.h>
#include 
#include<unistd.h>
int main()
{
    pid_t pid;
    int r;
    char *ch=NULL;
    char *ch1=NULL;
    int readpipe[2];
    int writepipe[2];
    int a;
    int b;
    a=pipe(readpipe);
    b=pipe(writepipe);
      // check a and b

    pid=fork();
    // check pid

    if(pid==0)
    { //CHILD PROCESS
            close(readpipe[1]);
            close(writepipe[1]);
            read(readpipe[0],ch,sizeof(ch));
            printf("\nREAD = %s",ch);
            close(readpipe[0]);
            ch1="YES";
            write(writepipe[1],ch1,sizeof(ch1));
            close(writepipe[1]);
    }
    else
    { //PARENT PROCESS
            close(writepipe[0]);
            close(writepipe[1]);
            ch="HI!! YOU THERE";
            write(readpipe[1],ch,sizeof(ch));
            close(readpipe[1]);
            read(writepipe[1],ch1,sizeof(ch1));
            printf("\nACK RECEIVED %s",ch1);
            close(writepipe[1]);
    }
    return 0;
}

Thanks...:)

Posted 18-Mar-14 22:43pm

Babita22

Updated 29-Apr-22 21:21pm

Richard MacCutchan

v2

Add a Solution

Comments

Babita22 19-Mar-14 5:02am

thanks @Richard for making it look clear. How to do it btw?

Richard MacCutchan 19-Mar-14 16:34pm

Click the Improve question link, and you can edit your question. You will then see the <pre> tags that I added around your code. Why not look at all the menu items above the edit window to see what they are there for?

4 solutions

Solution 1

I see two problems (there may be more) ...

1. In the CHILD PROCESS half of the code, you close writepipe[1] and then write to it.

2. In the PARENT PROCESS half of the code, you close BOTH writepipe handles but later close writepipe[1] again.

Posted 19-Mar-14 9:14am

bling

Solution 4

Write a C Program which will create a pipe. Write your name on the pipe from write end. Then read data from pipe from the read end. Then display data on terminal.

Posted 29-Apr-22 21:21pm

Member 15620144

Solution 3

#include <stdio.h>
#include <unistd.h>
#include <sys types.h="">
#include <stdlib.h>
#include <memory.h>

int main() {
//for parent to child
int parentToChild[2];

//for child to parent
int childToParent[2];

//string data
char message1[] = "massage from child to parent\n";
char message2[] = "message from parent to child\n";
char readBuffer[120];
pipe(parentToChild);
pipe(childToParent);
int processId , bytes;

if((processId = fork())== -1){
printf("error while creating a child process");
}

if(processId == 0){
//child process here
//send message from child to parent
close(childToParent[0]);
write(childToParent[1] , message1 , strlen(message1)+1);

//recive message from parent
close(parentToChild[1]);
bytes = read(parentToChild[0] , readBuffer , sizeof(readBuffer));
printf("%s",readBuffer);

// exit(1);
}

if(processId !=0 ){
//parent process here
//send message from parent to child
close(parentToChild[0]);
write(parentToChild[1] , message2 , strlen(message2)+1);

//recieve message from child
close(childToParent[1]);
bytes = read(childToParent[0] , readBuffer , sizeof(readBuffer));
printf("%s", readBuffer);
// exit(1);
}

return 0;
}

Posted 25-May-18 1:30am

Member 13844341

Comments

Richard MacCutchan 25-May-18 7:37am

Already answered FOUR years ago.

Add a Solution

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Babita22 · Accepted Answer · 2014-03-20T21:15:00

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include<wait.h>
int main(void)
{
        pid_t pid;
        int r;
        char buf[1024];
        char cp[50];
        char ans;
        int readpipe[2];
        int writepipe[2];
        long int a;
        int b;
        a=pipe(readpipe);
        b=pipe(writepipe);

        if (a == -1) { perror("pipe"); exit(EXIT_FAILURE); }
        if (b == -1) { perror("pipe"); exit(EXIT_FAILURE); }
        printf("\nSIZE OF CP IS %d",sizeof(cp));
        printf("\nSEND SOMETHING TO CHILD PROCESS\t");
        scanf("%[^\n]%*c",&ans);
        fflush(stdin);
        pid=fork();
        if(pid==-1)
        {
                printf("pid:main");
                exit(1);
        }
        while(ans=='y' || ans=='Y')
        {
                if(pid==0)
                { 
                //CHILD PROCESS
                         if(ans=='n')
                        {
                                //a=getpid();
                                //printf("\nPARENT PROCESS a=%ld",a);
                                kill(pid,SIGKILL);
                        }

                        close(readpipe[1]);
                        close(writepipe[0]);
                        if(read(readpipe[0],buf,sizeof(buf)) < 0)
                        {
                            break;
                        }
                        printf("\nChild Process Read: %s\n",buf);
                        printf("\n(child)Enter data:\t");
                        fflush(stdin);
                        fgets(cp, 50, stdin);
                        printf("\nData Written to Parent%s",cp);
                        if(/*!strncmp("Q",cp,1) || */write(writepipe[1],cp,strlen(cp)+1) < 0)
                        {
                            break;
                        }
                        //printf("\nSEND SOMETHING TO PARENT PROCESS\t");
                        //fflush(stdin);
                        //scanf(" %[^\n]%*c",&ans);

                }
                else
                {
                        close(readpipe[0]);
                        close(writepipe[1]);
                        printf("\n(Parent)Enter data\t");
                        fgets(cp, 50, stdin);
                        printf("\nData Writtent to Child: %s",cp);
                        if(/*!strncmp("Q",cp,1) ||*/ write(readpipe[1],cp,strlen(cp)+1) < 0)
                        {
                            break;
                        }        

                        if(read(writepipe[0],buf,sizeof(buf)) < 0)
                        {
                            break;
                        }
                        printf("\nParent Process Read: %s\n",buf);
                        printf("\nSEND SOMETHING TO CHILD PROCESS\t");
                        fflush(stdin);
                        scanf(" %[^\n]%*c",&ans);
                        if(ans=='n')
                        {
                                kill(pid,SIGKILL);
                        }
                }
//              printf("\nSEND SOMETHING TO CHILD PROCESS\t");
//              scanf("%[^\n]%*c",&ans);

        }
        close(readpipe[1]);
        close(writepipe[0]);
        close(readpipe[0]);
        close(writepipe[1]);
        return 0;
}

two way communication between child and parent processes in C using pipes

4 solutions

Solution 2

Solution 1

Solution 4

Solution 3

Add your solution here

Preview 0

two way communication between child and parent processes in C using pipes

4 solutions

Solution 2

Solution 1

Solution 4

Solution 3

Add your solution here

Preview 0

Existing Members

...or Join us