C++ character array not being read right through pipe

Question

I'm trying to check that the cmd variable is set to "LISTALL" but it isn't when I try printing it out.

#include <stdio.h>
#include <unistd.h>
#include <cstring>
#include <stdlib.h>
#include <iostream>
#include <sys/wait.h>

int main(int argc, char **argv)
{   
    pid_t cPid = fork();
    int P2C[2];
    int C2P[2];
    pipe(P2C);
    pipe(C2P);

    char cmd[50];
    char* listOfProcesses = new char[1024];

    if (cPid == 0)
    {
        ...
        read(P2C[0], cmd, 50);  
        printf("%s\n", cmd);
        if(strcmp(cmd,"LISTALL") == 0)
        {
            //printf("Executing the command: %s", cmd);
            write(C2P[1], getlistOfProcesses("ps -ax -o pid,cmd"), 1024);
            ...
        }
    }
    else if (cPid > 0)
    {
        ...
        write(P2C[1], "LISTALL", 50);
        wait(NULL);
        read(C2P[0], listOfProcesses,1024);
        ...
    }
    else
    {
        // fork failed
        printf("Forking failed!\n");
        exit(1);
    }
    return 0;
}

What I get from that is a mini box symbol with 00 at the top and 01 or 02 at the bottom. I tried pasting the symbol here but it doesn't show.

Answer 1

You create 4 pipes: two in the parent process and two in the child process.

Create the pipes before forking! Then fork, then check whether you are in the parent process or in the child process.

That way you have only two pipes, both processes know about these pipes and can communicate by reading or writing to the appropriate file descriptors of the pipes.