c++ - Interactive two-way communication (using pipes) between child and parent processes -
i trying create child process, redirect stdin , stdout parent process, , interact child process. is, parent process should able receive input child, process it, , provide output child, , cycle repeats (like user interaction shell, end goal: simulate user interaction).
thus far have been able create , redirect pipes (the code below echoes input on parent process, user, through child). problem can once, child terminates after first i/o cycle, , sigpipe. how can keep child alive, , have read pipe when parent writes it?
p.s. know except can used simulate user interaction, need access returned data custom analysis, , i'd go way academic purposes.
#include <iostream> #include <string> #include <sstream> #include <unistd.h> #include <stdio.h> #include <sys/wait.h> #include <limits.h> #include <sys/types.h> #include <cstdlib> #define max_cmd_size 256 #define max_buff_size 512 #define num_pipes 2 #define parent_read_pipe pipes[0] #define parent_write_pipe pipes[1] #define read_end 0 #define write_end 1 #define parent_read_fd parent_read_pipe[read_end] #define parent_write_fd parent_write_pipe[write_end] #define child_read_fd parent_write_pipe[read_end] #define child_write_fd parent_read_pipe[write_end] int pipes[num_pipes][2]; int main() { pipe(parent_read_pipe); pipe(parent_write_pipe); pid_t process_id = fork(); if (process_id<0) //throw diag::diagerror("error: error during fork()"); {std::cerr<<"error: error during fork()"; exit(1);} else if (process_id==0) {//child process dup2(child_read_fd, stdin_fileno); dup2(child_write_fd, stdout_fileno); close(child_read_fd); close(child_write_fd); close(parent_read_fd); close(parent_write_fd); char buffer[max_buff_size]; int count = read(stdin_fileno, buffer, max_buff_size-1); if (count >= 0) { buffer[count] = 0; printf("%s", buffer); } else //{throw diag::diagerror("io error");} {std::cerr<<"error: error during fork()"; exit(1);} exit(0); } else {//parent process close(child_read_fd); close(child_write_fd); char buffer[max_buff_size]; std::string temp=""; while(std::getline(std::cin,temp)) { write(parent_write_fd, temp.c_str(), temp.size()); //wait(&status); int count = read(parent_read_fd, buffer, max_buff_size-1); if (count >= 0) { buffer[count] = 0; printf("%s", buffer); } else //{throw diag::diagerror("io error");} {std::cerr<<"error: error during fork()"; exit(1);} } } }
your child process exits after 1 read:
if (process_id<0) throw diag::diagerror("error: error during fork()"); else if (process_id==0) {//child process ..... exit(0); /* <-- here */ } this of course causes pipe(s) closed , parent receives sigpipe while trying write pipe nobody reads anymore. parent code uses loop read/write to/from child - simmilar thing in child code - run in loop instead of exiting. can use special string of characters cause child process exit loop , terminate.
besides - if want read/write using stdin , stdout - invoke exec() after duplicated descriptors dup2 , closed right pipe ends. in child process use normal c++ streams std::cin , std::cout. of course requires refactoring child code separate program.
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