C 进程间通信--有名管道，无名管道

1．管道的概念

 管道是单向的、先进先出的，它把一个进程的输出和另一个进程的输入连接在一起。

一个进程（写进程）在管道的尾部写入数据，另一个进程（读进程）从管道的头部读出数据。

数据被一个进程读出后，将被从管道中删除，其它读进程将不能再读到这些数据。

管道提供了简单的流控制机制，进程试图读空管道时，进程将阻塞。同样，管道已经满时，进程再试图向管道写入数据，进程将阻塞

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

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

int main(){
        int pipe_fd[2];
        pid_t pid;
        if(pipe(pipe_fd)<0){
                perror("pipe");
                return 1;
        }
        pid = fork();
        if(pid==0){
                sleep(3);
                char buf[128];
                memset(buf,'\0',strlen(buf));
                printf("%d",strlen(buf));
                if(read(pipe_fd[0],buf,128)!=-1){
                        printf("child recv str:%s\n",buf);
                }
                exit(0);
        }else{
                char* str = "jenkin";
                char* str1 = "jenkin1";
                if(write(pipe_fd[1],str,strlen(str))!=-1){
                        printf("parent write str : %s\n",str);
                }
                if(write(pipe_fd[1],str1,strlen(str1))!=-1){
                        printf("parent write str : %s\n",str1);
                }
                waitpid(pid,NULL,0);
                close(pipe_fd[0]);
                close(pipe_fd[1]);
        }
        return 0;
}

//有名管道A

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
int main(){
    if (mkfifo ("myfifo", 0666) == -1)
        {
            perror ("mkfifo");
            exit (EXIT_FAILURE);
        }
    int fd = open ("myfifo", O_RDWR, 0666);
    if (fd == -1)
        {
            perror ("open");
            exit (EXIT_FAILURE);
        }
    char text[] = "this is jenkin test";
    size_t towrite = strlen(text);
    ssize_t written = write (fd, text, towrite);
    if (written == -1)
        {
            perror ("write");
            exit (EXIT_FAILURE);
        }
        sleep(10);
    if (close (fd) == -1)
        {
            perror ("close");
            exit (EXIT_FAILURE);
        }
    if (unlink ("myfifo") == -1)
        {
            perror ("unlink");
            exit (EXIT_FAILURE);
        }
    return 0;
}

//有名管道B

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <sys/stat.h>
int main(){
    int fd = open ("myfifo", O_RDWR, 0666);
    if (fd == -1)
        {
            perror ("open");
            exit (EXIT_FAILURE);
        }
    char text[1024];
        ssize_t readed = read (fd, text, 1024);
    if (readed == -1)
        { 
            perror ("read");
            exit (EXIT_FAILURE); 
        }
        printf("%s\n", text);
    if (close (fd) == -1)
        {
            perror ("close");
            exit (EXIT_FAILURE);
        }
    return 0;
}