c - C中的双向匿名管道

Question

我已经用 Ubuntu 用 C 语言编写了这个(希望是正确的)匿名管道，但我无法双向连接。我怎样才能以最简单的方式解决这个问题，从 child 到 parent 以及从 parent 到 child ？

int main() {
int ret_val;
int pfd[2];
char buff[32];
char string1[]="String for pipe I/O";

ret_val = pipe(pfd);   

if (fork() == 0) {
   // child 
   close(pfd[0]); // close the read end 
   ret_val = write(pfd[1],string1,strlen(string1)); /*Write to pipe*/
   if (ret_val != strlen(string1)) {
      printf("Write did not return expected value\n");
      exit(2); // Print error message and exit
   }
}
else {
   // parent
   close(pfd[1]); /* close the write end of pipe */
   ret_val = read(pfd[0],buff,strlen(string1)); /* Read from pipe */
   if (ret_val != strlen(string1)) {
      printf("Read did not return expected value\n");
      exit(3);                       /* Print error message and exit */
   }
   printf("parent read %s from the child program\n",buff);

}
exit(0);
}

Answer 1

见下文，它只能以这种方式工作，因为管道是 4KB 缓冲并且字符串较小，否则可能会陷入死锁。

#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

int main() {
    int ret_val;
    int pfd[2];
    int dfp[2];
    char buff[32];
    char string1[]="String for pipe I/O";
    char string2[]="String 2 for pipe I/O";

    ret_val = pipe(pfd), pipe(dfp);

    pid_t pid = fork();
    if (0 > pid) {
        printf("Error forking\n");
        exit(1);
    }
    if (pid == 0) {
        // child
        close(pfd[0]); // close the read end
        close(dfp[1]); // close the write end
        ret_val = write(pfd[1],string1,strlen(string1)); /*Write to pipe*/
        if (ret_val != strlen(string1)) {
            printf("Write did not return expected value\n");
            exit(2); // Print error message and exit
        }
        ret_val = read(dfp[0],buff,strlen(string2)); /* Read from pipe */
        if (ret_val != strlen(string2)) {
            printf("Read did not return expected value\n");
            exit(3);                       /* Print error message and exit */
        }
        printf("child read '%s' from the parent program\n",buff);
    }
    else {
        // parent
        close(pfd[1]); /* close the write end of pipe */
        close(dfp[0]); /* close the read end */
        ret_val = write(dfp[1],string2,strlen(string2)); /*Write to pipe*/
        if (ret_val != strlen(string2)) {
            printf("Write did not return expected value\n");
            exit(2); // Print error message and exit
        }
        ret_val = read(pfd[0],buff,strlen(string1)); /* Read from pipe */
        if (ret_val != strlen(string1)) {
            printf("Read did not return expected value\n");
            exit(3);                       /* Print error message and exit */
        }
        printf("parent read '%s' from the child program\n",buff);
        wait(NULL);
    }
    exit(0);
}