进程间通信编程(2) - 无名管道

管道包括无名管道和有名管道两种，前者用于父进程和子进程间的通信，后者可用于运行于同一系统中的任意两个进程间的通信。

无名管道由pipe（）函数创建：
int pipe(int filedis[2])；
当一个管道建立时，它会创建两个文件描述符：filedis[0] 用于读管道， filedis[1] 用于写管道

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

int main()
{
    int pipe_fd[2];
    pid_t  pid;
    char buf_r[50];
    char * p_wbuf;
    int r_num;

    memset(buf_r,0,sizeof(buf_r));

    if (pipe(pipe_fd) < 0)
    {
        perror("pipe error :");
        exit(-1);
    }

    if ((pid = fork()) == 0)
    {
        close(pipe_fd[1]);
        sleep(2);

        if ((r_num = read(pipe_fd[0],buf_r,50)) > 0)
        {
            char * p = buf_r;

            while(*p != '\0')
            {
                if(*p >= 'a' && *p <= 'z')
                {
                    *p = *p - 32;
                }
                p++;
            }

            printf("\n%d numbers read from the pipe,  is %s \n",r_num,buf_r);
        }

        close(pipe_fd[0]);
        exit(0);
    }

    else if(pid > 0)
    {
        close(pipe_fd[0]);

        if(write(pipe_fd[1],"HeLlo",5) != -1)
        {
            printf("parent write pipe  success!\n");
        }
    }

    close(pipe_fd[1]);
    sleep(3);
    waitpid(pid,NULL,0);
    exit(0);

    return 0;
}

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

int main()
{
    int pipefd[2];
    int ret;
    pid_t pid;
    char buffer[512] = {0};

    ret = pipe(pipefd);
    if (-1 == ret)
    {
        perror("pipe");
        return -1;
    }

    pid = fork();
    switch (pid)
    {
        case -1:
            perror("fork");
            return -1;
        case 0:
            close(pipefd[1]);
            read(pipefd[0], buffer, sizeof(buffer));
            printf("Read from pipe: %s", buffer);
            exit(0);
        default:
            close(pipefd[0]);
            sleep(2);
            write(pipefd[1], "Hello Linux\n", strlen("Hello Linux\n"));
    }
    wait(NULL);

    return 0;
}