linux pipes example

c_pipes_ipc.cpp

#include <iostream>
#include <sstream>
#include <cstdio>
#include <string>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>

/*
This illustrates how to communicate with an external application by sending text to stockfish and receiving text from stockfish.
*/

#define READ  0
#define WRITE 1


int main(int argc, char *argv[])

{
    int pipe_to_stockfish[2];
    int pipe_from_stockfish[2];

    if ((pipe2 (pipe_to_stockfish, O_NONBLOCK) < 0) || (pipe2 (pipe_from_stockfish, O_NONBLOCK) < 0))
    {
        perror ("pipe failure");
        exit (EXIT_FAILURE);
    }

    auto pid = fork();
    if (pid == 0) {
        /* Child process */
        // Close unused ends of pipes
        close (pipe_to_stockfish[WRITE]);
        close (pipe_from_stockfish[READ]);

        // Redirect standard input and output to the pipes
        dup2 (pipe_to_stockfish[READ], STDIN_FILENO);
        dup2 (pipe_from_stockfish[WRITE], STDOUT_FILENO);

        // Close the duplicate file descriptors
        close (pipe_to_stockfish[READ]);
        close (pipe_from_stockfish[WRITE]);

        execlp("/usr/games/stockfish", "/usr/games/stockfish", NULL);

        exit(0);
    }
    else {
        /* Parent process */
        close (pipe_to_stockfish[READ]);
        close (pipe_from_stockfish[WRITE]);


        std::string s = "uci\n";
        auto nbytes = write(pipe_to_stockfish[WRITE], s.c_str(), s.size());
        sleep(1);


        std::stringstream ss;
        ssize_t r;

        do {
            char buf[80] = {0};
            r = read(pipe_from_stockfish[READ], buf, sizeof(buf)- 1);
            if (r > 0)
                ss << buf;
        } while ((r != 0));
        std::cout << "parent process received " << r << " bytes" << std::endl;
        std::cout << ss.str();
    }

    wait(NULL);

    return 0;
}