Named pipe similar to “mkfifo” creation, but bidirectional

You could open() your pipe O_RDONLY | O_NONBLOCK, and if you want the C stream, you can get it with fdopen(). However, there might be a problem with the select() - AFAIK, a pipe fd open for reading that has no writer is always prepared for reading, and read() returns 0, so the select() would fire indefinitely.

A kludgy way of overcoming this would be to open the pipe O_RDWR; that is, have at least one writer (your C++ program). Which would solve your problem anyway.

I'd suggest writing your own function to do the piping/forking/system-ing for you. You could have the function spawn a process and return read/write file descriptors, as in...

typedef void pfunc_t (int rfd, int wfd);

pid_t pcreate(int fds[2], pfunc_t pfunc) {
    /* Spawn a process from pfunc, returning it's pid. The fds array passed will
     * be filled with two descriptors: fds[0] will read from the child process,
     * and fds[1] will write to it.
     * Similarly, the child process will receive a reading/writing fd set (in
     * that same order) as arguments.
    */
    pid_t pid;
    int pipes[4];

    /* Warning: I'm not handling possible errors in pipe/fork */

    pipe(&pipes[0]); /* Parent read/child write pipe */
    pipe(&pipes[2]); /* Child read/parent write pipe */

    if ((pid = fork()) > 0) {
        /* Parent process */
        fds[0] = pipes[0];
        fds[1] = pipes[3];

        close(pipes[1]);
        close(pipes[2]);

        return pid;

    } else {
        close(pipes[0]);
        close(pipes[3]);

        pfunc(pipes[2], pipes[1]);

        exit(0);
    }

    return -1; /* ? */
}

You can add whatever functionality you need in there.