简单的叉子和管道

Question

我想了解我的操作系统类中的分叉和管道。我不确定为什么第二个子进程不打印出meminfo。它似乎写入管道，如果我打印出来，但它不会读取第二个子进程中的任何内容。我错过了什么让第二个进程从管道读取？

#include <stdlib.h> 
#include <stdio.h> 
#include <unistd.h> 
#include <fcntl.h> 
#include <errno.h> 
#include <sys/wait.h> 

#define R_FILE "/proc/meminfo" 
#define BSIZE 256 
#define READ_END 0 
#define WRITE_END 1 

int main() 
{ 
    int status; 
    pid_t pid_1, pid_2; 

    int pipefd[2]; 
    pipe(pipefd); 

    pid_1 = fork(); 
    if (pid_1 == 0) { 
    /* process a */ 

    int rfd; 
    size_t rsize; 
    char buf[BSIZE]; 
    close(pipefd[READ_END]); 
    if ((rfd = open(R_FILE, O_RDONLY)) < 0) { 
     fprintf(stderr, "\nError opening file: %s. ERROR#%d\n", R_FILE, errno); 
     return EXIT_FAILURE; 
    } 

    /* read contents of file and write it out to a pipe */ 
    while ((rsize = read(rfd, buf, BSIZE)) > 0) { 
     /* This should write to a pipe */ 
     write(pipefd[1], buf, rsize); 
    } 

    close(pipefd[WRITE_END]); 
    close(rfd); 
    return 0; 
    } 

    pid_2 = fork(); 
    if (pid_2 == 0) { 
    /* process b */ 
    size_t rsize; 
    char buf[BSIZE]; 
    /* read from pipe and write out contents to the terminal */ 
    close(pipefd[WRITE_END]); 
    /* Thishis should read from a pipe */ 

     while ((rsize = read(pipefd[1], buf,BSIZE)) > 0) { 
     write(STDOUT_FILENO, buf, rsize); 

     } 

    close(pipefd[READ_END]); 

    return 0; 
    } 

    /* shell process */ 
    if ((waitpid(pid_1, &status, 0)) == -1) { 
    fprintf(stderr, "Process 1 encountered an error. ERROR%d", errno); 
    return EXIT_FAILURE; 
    } 

    if ((waitpid(pid_2, &status, 0)) == -1) { 
    fprintf(stderr, "Process 2 encountered an error. ERROR%d", errno); 
    return EXIT_FAILURE; 
    } 

    return 0; 
} 

Answer 1

在处理b你可能读错了fd read(pipefd[1], buf,BSIZE)。将其替换为read(pipefd[READ_END], buf,BSIZE)。