文章目录

举例1

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

int main1 (void)
{
    int fd, new_fd;
    fd = open ("write.txt", O_RDWR | O_CREAT, 0644);
    if (fd == -1)
    {
        perror ("open");
        exit (EXIT_FAILURE);
    }
    new_fd = dup (fd);
    printf ("fd = %d\nnew_fd = %d\n", fd, new_fd);
    write (fd, "hello", strlen("hello"));
    close (fd);
    write (new_fd, "world", strlen("world"));
    close (new_fd);
    return 0;
}

int main (void)
{
    int new_fd;
    new_fd = dup (1);
    write (1, "hello", strlen("hello"));
    write (new_fd, "world\n", strlen("world\n"));
    close (new_fd);
    return 0;
}

new\_fd = dup (fd);
给new\_fd分配一个新的文件描述符,使其和fd指向的文件一致,以后使用new\_fd或fd均可
new\_fd = dup (1);
使new\_fd指向标准输出

举例2

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

#define handler_error(msg) \
    {perror(msg);exit(EXIT_FAILURE);}

int main (void)
{
    int fd, new_fd;
    char *buf = "hello world\n";

    fd = open ("data.log", O_RDWR | O_CREAT, 0644);
    if (fd == -1)
        handler_error("open");

    new_fd = dup2 (fd, 1);
    if (new_fd == -1)
        handler_error("dup2");

    printf ("fd: %d\n new_fd: %d\n", fd, new_fd);
    write (1, buf, strlen(buf));
    close (fd);

return 0;
}

new\_fd = dup2 (fd, 1);
给标准输出1赋值为文件描述符fd,以后标准输出全部重定向到fd指向的文件中,返回值为赋予新含义的文件描述符,本例中返回1(这里1和fd指向同一文件)

举例3

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

int main (void)
{
    int pipe_fd[2];
    if (pipe (pipe_fd) == -1)
    {
        perror ("pipe");
        exit (EXIT_FAILURE);
    }
    else
    {
        int ret_from_fork;
        ret_from_fork = fork ();
        if (ret_from_fork == 0)  // child process
        {
        //    close (1);
            dup2 (pipe_fd[1], 1);
            execlp ("cat", "cat", "dup.c", NULL);
        }
        else
        {
        //    close (0);
            dup2 (pipe_fd[0], 0);
            close (pipe_fd[1]);
            execlp ("grep", "grep", "include", NULL);
        }
    }
    return 0;
}

该例实现了一个cat dup.c|grep include功能,很值得借鉴


linuxC多进程通讯---无名管道dup教程学无止境966发布了349 篇原创文章 · 获赞 6 · 访问量 9628 私信 关注

标签: int, include, close, dup, new, fd, linuxC, 无名

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