命名管道使用

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命名管道

命名管道相对于管道（pipe）有许多优点：

1、命令管道可以用于非父子关系的进程的通信；而pipe只能用于父进程创建子进程，然后进行通信，多用于shell命令。

2、命令管道是以文件的形式保存在文件中，因此可以提供给多个知道进程名字的进程通信。

3、命令管道又叫FIFO 使用mkfifo()创建。

简单的例子

client创建一个有名管道，server创建一个有名管道。client通过server的管道将自身的pid传送给server，server将通过client的管道返回值

server

//============================================================================// Name        : server.cpp// Author      : Tian// Version     :// Copyright   : Your copyright notice// Description : Hello World in C++, Ansi-style//============================================================================#include <sys/types.h>#include <sys/stat.h>#include <sys/ipc.h>#include <sys/errno.h>#include <unistd.h>#include <fcntl.h>#include <stdio.h>#include <string.h>#include <stdlib.h>#define  MAXLINE 1024#define  FIFO_MODE (S_IRUSR | S_IWUSR | S_IRGRP |S_IROTH)#define  SERV_FIFO  "/tmp/serv.fifo"int main(int argc,char **argv) {int readfifo,writefifo,dummyfd;int fd;char *ptr,buff[MAXLINE+1],fifoname[MAXLINE];pid_t pid;ssize_t n;if( (mkfifo(SERV_FIFO,FIFO_MODE) < 0 ) && (errno != EEXIST) )  //创建printf("can't create %s",SERV_FIFO);readfifo = open(SERV_FIFO,O_RDONLY|O_NONBLOCK,0); // O_NONBLOCK不阻塞，否则可能会阻塞在此dummyfd = open(SERV_FIFO,O_RDONLY|O_NONBLOCK,0);while( (n = read(readfifo,buff,MAXLINE)) >=0 ){if(n == 0)continue;if(buff[n-1] == '\n')n--;buff[n] = '\0';if( (ptr = strchr(buff,'\0')) == NULL ){printf("bogus request :%s",buff);continue;}*ptr++ = 0;pid = atol(buff); snprintf(fifoname,sizeof(fifoname),"/tmp/fifo.%ld",(long)pid);if( (writefifo = open(fifoname,O_WRONLY,0)) < 0){printf("cannot open:%s",fifoname);continue;}if( (fd=open(ptr,O_WRONLY,0)) < 0 ){snprintf(buff+n,sizeof(buff)-n,":can't open,%s\n",strerror(errno));n = strlen(ptr);write(writefifo,ptr,n);close(writefifo);}else {while( (n = read(fd,buff,MAXLINE)) > 0 )write(writefifo,buff,n);close(fd);close(writefifo);}}exit(0); //#include<fcntl.h>}

client:

//============================================================================// Name        : server.cpp// Author      : Tian// Version     :// Copyright   : Your copyright notice// Description : Hello World in C++, Ansi-style//============================================================================#include <iostream>#include <sys/types.h>#include <sys/stat.h>#include <sys/ipc.h>#include <sys/errno.h>#include <unistd.h>#include <fcntl.h>#include <stdio.h>#include <string.h>#include <stdlib.h>using namespace std;#define  MAXLINE 1024#define  FIFO_MODE (S_IRUSR | S_IWUSR | S_IRGRP |S_IROTH)#define  SERV_FIFO "/tmp/serv.fifo"int main(int argc,char **argv) {int readfifo,writefifo;char *ptr,buff[MAXLINE+1],fifoname[MAXLINE];pid_t pid;size_t len;ssize_t n;pid = getpid();snprintf(fifoname,sizeof(fifoname),"/tmp/fifo.%ld",(long)pid);if( (mkfifo(fifoname,FIFO_MODE) <0) && (errno!=EEXIST))printf("can't create %s",fifoname);snprintf(buff,sizeof(buff),"%ld",(long)pid);len = strlen(buff);ptr = buff+len;//fgets(ptr,MAXLINE-len,stdin);//len = strlen(buff);writefifo = open(SERV_FIFO,O_WRONLY,0);write(writefifo,buff,len);readfifo = open(fifoname,O_RDONLY|O_NONBLOCK,0);while((n = read(readfifo,buff,MAXLINE)) >= 0){if(n == 0)continue;write(STDOUT_FILENO,buff,n);}close(readfifo);unlink(fifoname);exit(0);}

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