为什么子进程“读取”功能不返回（我认为它将返回-1），并且子进程“ printf”功能不起作用

Question

Why the son process "read" function don't return (I think it will return -1), and the son process 'printf' function does not work.

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

int main() {
    int fd[2];
    pipe(fd);
    pid_t pid = fork();
    if(pid == 0) {
        char buf[128] = {0};
        int ret = read(fd[0], buf, sizeof buf);
        printf("Son ret is %d\n", ret);
        write(STDOUT_FILENO, buf, ret);
    }
    else if(pid > 0){
        char buf[128] = "hello\n\0";
        write(fd[1], buf, sizeof buf);
        memset(buf, 0, sizeof buf);
        int ret = read(fd[0], buf, sizeof buf);
        printf("Dad ret is %d\n", ret);
        write(STDOUT_FILENO, buf, ret);
    }
    return 0;
}

Answer 1

1. It is not defined which process will get the buffer. Maybe the parent, maybe the child, maybe both will get a half of it each. Maybe in your experiment the father gets all of the buffer, but nobody guarantees that it will always happen.
2. A process should close an unused write end of its pipe, otherwise it will never see an EOF on the read end. So the child should call close(fd[1]) before doing anything else.
3. (Unrelated) An explicit \\0 at the end of a string literal is unnecessary.