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Does anyone see any mistakes here? I am trying to get a message via a pipe, from my parent to child


Does anyone see any mistakes here? I am trying to get a message via a pipe, from my parent to child

By : Rei Valera
Date : October 23 2020, 06:10 PM
This might help you Without examining the rest of your code, you need to call pipe() before you call fork() so the pipe can be used by both the parent and the child process. If you call pipe() after you call fork(), the pipe is only usable by that one process.
More like this:
code :
int main(int argc, char const *argv[])
{
    int mypipefd[2];

    if ( pipe( mypipefd ) == -1 )
    {
        perror("Pipe failed\n");
        exit(EXIT_FAILURE);
    }

    pid_t pid = fork();
    if (pid > 0)
    {
        storeEngine(mypipefd);
    } 
    .
    .
    .


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C Pipe: Parent to read from child before child ends

C Pipe: Parent to read from child before child ends


By : TimeKill
Date : March 29 2020, 07:55 AM
may help you . You are not correct. Try to add the sleep(120) call just before closing the write end of pipe in the 'child' part and run your application.
How can the child process read stdout from the pipe and the parent process write stdin to the pipe?

How can the child process read stdout from the pipe and the parent process write stdin to the pipe?


By : Mario Chaushki
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , The result of fork() is that one process becomes two (by asexual reproduction). So while it is still the case that exactly one branch of the if/else block will be taken in a process, there are two processes, and one path will be taken by each.
More specifically, look at what fork() returns: a PID to the parent, and 0 to the new child. Apart from that the two processes are almost identical. So the if (cpid == 0) check is a common pattern after fork() so that you can proceed with distinct logic in each process. In your case, that's reading in one process and writing in the other.
Does parent see pipe eof on child exit?

Does parent see pipe eof on child exit?


By : user3918452
Date : March 29 2020, 07:55 AM
may help you . The standard I/O library uses read(2) and write(2) under the hood; the behavior of read(2) is to return 0 to indicate EOF when there is no more data available in the pipe and no active writers (the standard I/O library then converts this to the negative EOF constant that we all know).
So, if you set things up properly, getline() will not hang and it will return -1.
read integer from user and write into child pipe and then parent pipe read from it

read integer from user and write into child pipe and then parent pipe read from it


By : Parvathi S
Date : March 29 2020, 07:55 AM
To fix this issue There are several issues here:
You're prompting for N in the child process, however the parent process is the one that receives input from the terminal. So by the time you enter "6", the parent process has exited and you're entering that value to the shell. Move the printf and scanf to before the fork and you should be able to read that value properly. Your case 1 will not be entered for the case when fork() returns from the parent, which seems to be your intent. fork() returns the pid of the child to the parent. Because the special init process has pid 1, this will never be true. Change case 1: to default to process the parent process. You're not using break at the end of your switch cases. In C, switch cases "fall through", meaning that once the statement for one case are complete, it will continue running the statements for the following case. The break statement at the end of each case prevents that from happening.
code :
#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<fcntl.h>
#define BUFSIZE 80

int main()
{
    int fd[2],n,i,h;
    pid_t pid;     // to capture the child pid
    char buf[BUFSIZE];
    // prompt for N before forking
    printf("Enter N :");
    scanf("%d",&n);
    pipe(fd);
    switch((pid=fork()))   // saving the child pid in case we want to use it later
    {
        case -1 :
            printf("Fork Error");
            exit(0);     // no break needed here because of exit
        case 0  :
            close(fd[0]);
            write(fd[1],&n,sizeof(n));
            close(fd[1]);
            break;       // end of case 0
        default :
            close(fd[1]);
            n=read(fd[0],&h,sizeof(h));
            printf("h=%d\n",h);
            for(i=1;i<=h;i++)
            {
                if(i%2==1)
                {
                    //write(1,&i,n);
                    printf("%d\n",i);
                }
            }
            close(fd[0]);
            break;      // end of default case
    }
    exit(0);
}
Why child process pipe is showing in parent process with different pipe details

Why child process pipe is showing in parent process with different pipe details


By : user2292019
Date : March 29 2020, 07:55 AM
To fix this issue You have these things happening.
parent creates pipe 354240 stored in parentpip child1 is forked from parent, inheriting pipe 354240 parent creates pipe 354241 stored in child1pip child1 creates pipe 357693 stored in child1pip child2 is forked from child1, inheriting pipe 354240 and 357693
code :
int child1pip[2];
pipe(child1pip);

if(child1pid==0)
{
if(child1pid==0)
{
     int child1pip[2];
     pipe(child1pip
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