使用未命名管道的双向IPC

Question

我正在尝试通过管道运行expand命令以达到最大值。输入需要来自stdin，输出需要进入stdout。下面的预期输入和输出以及我目前正在经历的。目前它 似乎什么也没写给孩子，我也不知道为什么。如果有人可以帮助，那就更好了。谢谢大家的帮助。

  

预期的输入和输出：

     

$ ./ expand

     

> （x + 2）^ 2

     

x ^ 2 + 4 * x + 4

     

或

     

$ ./展开“（x + 2）^ 2”

     

x ^ 2 + 4 * x + 4

     

＃当前输入和输出：＃

     

$ ./ expand

     

> （x + 2）^ 2

     

>

     

或

     

$ ./展开“（x + 2）^ 2”

     

$

代码：

#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string>
#include <string.h>
#include <cstdio>
#include <cstdlib>
#include <fcntl.h>
#include <errno.h>
#include <iostream> // cin, cout
#include <signal.h>
using namespace std;


int main(int argc, char* argv[]) {
    pid_t pid;
    unsigned char c;
    int pp[2]; // parent writes to child(1) and parent reads from child (0)
    int cp[2]; // child writes to parent (1) and child reads from parent(0)
    string disable = "display2d:false$";
    string start = "expand(";
    string end = ");";
    string inp, sent;
    char tmp[BUFSIZ+1];


    if(pipe(pp) < 0|| pipe(cp) <0 ) {
        cerr<<"Pipe Failure" << endl;
        exit(1);
    }
    if((pid = fork()) < 0) {
        cerr<<"Fork Failure"<<endl;
        exit(2);
    }
    if(pid == 0) { // child process
        close(pp[1]); // unused pipes get closed
        close(cp[0]);
        dup2(pp[0],STDIN_FILENO); // copy stdin
        close(pp[0]);
        dup2(cp[1],STDOUT_FILENO); // copy stdout
        close(cp[1]); // finish closing so exec doesn't see them
        execlp("maxima","maxima", "-q", (char*)0);
        exit(EXIT_FAILURE);
    }
    else {
        if(argc == 1) { // parent process
            close(pp[0]); // close unused ends of pipes
            close(cp[1]);
            while(1) {
                printf("> ");
                getline(cin,inp);
                if(inp == "quit") { // if quit, send close command
                    write(pp[1], "quit();" , strlen("quit();"));
                    close(pp[1]); //close pipes
                    close(cp[0]);
                }
                sent = disable+start+inp+end; // sends "display2d:false$expand(inp);\n
                write(pp[1], sent.c_str(), sent.length()+1);
                do {
                    read(cp[0], &c, 1);
                    write(STDOUT_FILENO, &c, 1);
                } while(c != '\n');
                close(pp[1]);
                waitpid(pid, NULL, 0);
                close(cp[0]);
            }

        }
        if(argc > 1) {
            close(pp[0]);
            close(cp[1]);
            for(int i = 1; i < argc; i++) {
                strcat(tmp, "expand(");
                strcat(tmp, argv[i]);
                strcat(tmp, ");");
                write(pp[1], tmp, strlen(tmp));
                write(pp[1], "\n", 1);
                do {
                    read(cp[0], &c, 1);
                    write(STDOUT_FILENO, &c, 1);
                    //fflush(stdout);
                } while(c != '\0');
            }
            write(pp[1], "quit()$\n", strlen("quit()$\n"));
            close(pp[1]);
            waitpid(pid, NULL, 0);
            close(cp[0]);
        }
    }
    return 0;
}