管道的字节流特性

#include <stdio.h>
#include <sys/wait.h>
#include <unistd.h>
#include <string.h>

#define BUF_SIZE 10

int main(int argc, char *argv[]) {
    int pfd[2];
    char buf[BUF_SIZE];
    ssize_t numRead;

    if(argc != 2 || strcmp(argv[1], "--help") == 0) {
        printf("%s string\n", argv[0]);
        return -1;
    }

    if(pipe(pfd) == -1) {
        fprintf(stderr, "pipe error.");
        return -1;
    }

    switch(fork()) {
    case -1:
        fprintf(stderr, "fork() error.");
        break;
    case 0:
        if(close(pfd[1]) == -1) {
            fprintf(stderr, "close error.");
            return -1;
        }
        for(;;) {
            numRead = read(pfd[0], buf, BUF_SIZE);
            if(numRead == -1) {
                fprintf(stderr, "read error.");
                return -1;
            }
            if(numRead == 0) {
                break;
            }
            if(write(STDOUT_FILENO, buf, numRead) != numRead) {
                fprintf(stderr, "write error");
                return -1;
            }
        }
        write(STDOUT_FILENO, "\n", 1);
        if(close(pfd[0]) == -1) {
            fprintf(stderr, "close error");
            return -1;
        }
        break;
    default:
        if(close(pfd[0]) == -1) {
            fprintf(stderr, "close error.");
            return -1;
        }
        if(write(pfd[1], argv[1], strlen(argv[1])) != strlen(argv[1])) {
            fprintf(stderr, "write error.");
            return -1;
        }
        if(close(pfd[1]) == -1) {
            fprintf(stderr, "close error.");
            return -1;
        }
        wait(NULL);
        break;
    }
    return 0;
}