Linux C++ run and communicate with new process

Question

I need to make a program that runs a process (my another programm) and can communicate with this process (sending stdin and recieving stdout). I have read about functions like <

Answer 1

The interface for POSIX functions C language only. But you can use them in C++.

Basically:

#include <unistd.h>
// Include some other things I forgot. See manpages.

int main()
{
    // Open two pipes for communication
    // The descriptors will be available to both
    // parent and child.
    int in_fd[2];
    int out_fd[2];

    pipe(in_fd);  // For child's stdin
    pipe(out_fd); // For child's stdout

    // Fork
    pid_t pid = fork();

    if (pid == 0)
    {
        // We're in the child
        close(out_fd[0]);
        dup2(out_fd[1], STDOUT_FILENO);
        close(out_fd[1]);

        close(in_fd[1]);
        dup2(in_fd[0], STDIN_FILENO);
        close(in_fd[0]);

        // Now, launch your child whichever way you want
        // see eg. man 2 exec for this.

        _exit(0); // If you must exit manually, use _exit, not exit.
                  // If you use exec, I think you don't have to. Check manpages.
    }

    else if (pid == -1)
        ; // Handle the error with fork

    else
    {
        // You're in the parent
        close(out_fd[1]);
        close(in_fd[0]);

        // Now you can read child's stdout with out_fd[0]
        // and write to its stdin with in_fd[1].
        // See man 2 read and man 2 write.

        // ...

        // Wait for the child to terminate (or it becomes a zombie)
        int status
        waitpid(pid, &status, 0);

        // see man waitpid for what to do with status
    } 
}

Don't forget to check error codes (which I did not), and refer to man pages for details. But you see the point: when you open file descriptors (eg. via pipe), they will be available to parent and child. The parent closes one end, the child closes one other end (and redirects the first end).

Be smart and not afraid of google and man pages.