管道（二）

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无名管道

测试代码：

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

#define ERR_EXIT(m) do { perror(m); exit(EXIT_FAILURE); }while(0)
#define TEST_SIZE 68*1024

int main(int argc, char *argv[])
{
    char a[TEST_SIZE];
    char b[TEST_SIZE];
    memset(a, 'a', sizeof(a));
    memset(b, 'b', sizeof(b));
    int pipefd[2];
    int ret = pipe(pipefd);
    if (ret == -1)
        ERR_EXIT("pipe_errro");

    pid_t pid;
    pid = fork();
    if(pid == 0) {
        close(pipefd[0]);
        ret = write(pipefd[1], a, sizeof(a));
        printf("apid = %d write %d bytes to pipefd\n", getpid(), ret);
        exit(0);
    }
    pid = fork();
    
    if(pid == 0) {
        close(pipefd[0]);
        ret = write(pipefd[1], b, sizeof(b));
        printf("bpid = %d write %d bytes to pipefd\n", getpid(), ret);
        exit(0);
    }
    close(pipefd[1]);
    sleep(1);
    int fd = open("test.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);
    char buf[1024 * 4] = {0};
    int n = 1;
    while(1) {
        ret = read(pipefd[0], buf, sizeof(buf));
        if (ret == 0)
        break;
        printf("n = %02d pid = %d read %d bytes from pipe buf[4096] = %c\n", n++, getpid(), ret, buf[4095]);
        write(fd, buf, ret);
    }
}