socket编程小问题:地址已经被使用——Address already in use

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很多socket编程的初学者可能会遇到这样的问题:如果先ctrl+c结束服务器端程序的话,再次启动服务器就会出现Address already in use这个错误,或者你的程序在正常关闭服务器端socket后还是有这个问题。正如下面的这段简单的socket程序。

 

server.c

#include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <stdlib.h> #define BUFFER_SIZE 40 int main() { char buf[BUFFER_SIZE]; int server_sockfd, client_sockfd; int sin_size=sizeof(struct sockaddr_in); struct sockaddr_in server_address; struct sockaddr_in client_address; memset(&server_address,0,sizeof(server_address)); server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = INADDR_ANY; server_address.sin_port = htons(12000); // 建立服务器端socket if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0))<0) { perror("server_sockfd creation failed"); exit(EXIT_FAILURE); } // 将套接字绑定到服务器的网络地址上 if((bind(server_sockfd,(struct sockaddr *)&server_address,sizeof(struct sockaddr)))<0) { perror("server socket bind failed"); exit(EXIT_FAILURE); } // 建立监听队列 listen(server_sockfd,5); // 等待客户端连接请求到达 client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,(socklen_t*)&sin_size); if(client_sockfd<0) { perror("accept client socket failed"); exit(EXIT_FAILURE); } // 接收客户端数据 if(recv(client_sockfd,buf,BUFFER_SIZE,0)<0) { perror("recv client data failed"); exit(EXIT_FAILURE); } printf("receive from client:%s/n",buf); // 发送数据到客户端 if(send(client_sockfd,"I have received your message.",BUFFER_SIZE,0)<0) { perror("send failed"); exit(EXIT_FAILURE); } close(client_sockfd); close(server_sockfd); exit(EXIT_SUCCESS); }

 

client.c

#include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <stdlib.h> #define BUFFER_SIZE 40 int main() { char buf[BUFFER_SIZE]; int client_sockfd; int len; struct sockaddr_in address;// 服务器端网络地址结构体 int result; client_sockfd = socket(AF_INET, SOCK_STREAM, 0);// 建立客户端socket address.sin_family = AF_INET; address.sin_addr.s_addr = inet_addr("127.0.0.1"); address.sin_port = htons(12000); len = sizeof(address); // 与远程服务器建立连接 result = connect(client_sockfd, (struct sockaddr *)&address, len); if(result<0) { perror("connect failed"); exit(EXIT_FAILURE); } printf("Please input the message:"); scanf("%s",buf); send(client_sockfd,buf,BUFFER_SIZE,0); recv(client_sockfd,buf,BUFFER_SIZE,0); printf("receive data from server: %s/n",buf); close(client_sockfd); return 0; }

 

      在成功的运行了第一次之后,当你再次启动服务器端程序时,./server就变得邪恶起来,在bind()这个函数中居然出现了Address already in use这个错误。

推荐:Linux下Socket编程的端口问题( Bind(): Address already in use )

[Linux下Socket编程的端口问题( Bind(): Address already in use )转载请注明 本文引用地址 http://blog.csdn.net/xl_xunzhao/archive/2008/10/23/3130037.aspx 最近在开发

                                 

      然后你开始迷惑了,难道是忘记将socket给关闭了,或是关闭socket的顺序不对?经过种种猜测与试验,你发现问题毫无进展......过了一会,当你再次抱着试试看的态度重新在linux的“黑色终端”中输入./server时,程序居然运行了,什么情况?究其原因,是socket选项在捣鬼。下面是IBM官网上对这一情况的具体解释,参见http://www.ibm.com/developerworks/cn/linux/l-sockpit/

      bind 普遍遭遇的问题是试图绑定一个已经在使用的端口。该陷阱是也许没有活动的套接字存在,但仍然禁止绑定端口(bind 返回 EADDRINUSE),它由 TCP 套接字状态 TIME_WAIT 引起。该状态在套接字关闭后约保留 2 到 4 分钟。在 TIME_WAIT 状态退出之后,套接字被删除,该地址才能被重新绑定而不出问题。

等待 TIME_WAIT 结束可能是令人恼火的一件事,特别是如果您正在开发一个套接字服务器,就需要停止服务器来做一些改动,然后重启。幸运的是,有方法可以避开 TIME_WAIT 状态。可以给套接字应用 SO_REUSEADDR 套接字选项,以便端口可以马上重用。

考虑清单 3 的例子。在绑定地址之前,我以 SO_REUSEADDR 选项调用 setsockopt。为了允许地址重用,我设置整型参数(on)为 1 (不然,可以设为 0 来禁止地址重用)。

      按照IBM的做法,我重新改写了server.c的代码。

server.c

 #include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <stdlib.h> #define BUFFER_SIZE 40 int main() { char buf[BUFFER_SIZE]; int server_sockfd, client_sockfd; int sin_size=sizeof(struct sockaddr_in); struct sockaddr_in server_address; struct sockaddr_in client_address; memset(&server_address,0,sizeof(server_address)); server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = INADDR_ANY; server_address.sin_port = htons(12000); // 建立服务器端socket if((server_sockfd = socket(AF_INET, SOCK_STREAM, 0))<0) { perror("server_sockfd creation failed"); exit(EXIT_FAILURE); } // 设置套接字选项避免地址使用错误 int on=1; if((setsockopt(server_sockfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on)))<0) { perror("setsockopt failed"); exit(EXIT_FAILURE); } // 将套接字绑定到服务器的网络地址上 if((bind(server_sockfd,(struct sockaddr *)&server_address,sizeof(struct sockaddr)))<0) { perror("server socket bind failed"); exit(EXIT_FAILURE); } // 建立监听队列 listen(server_sockfd,5); // 等待客户端连接请求到达 client_sockfd=accept(server_sockfd,(struct sockaddr *)&client_address,(socklen_t*)&sin_size); if(client_sockfd<0) { perror("accept client socket failed"); exit(EXIT_FAILURE); } // 接收客户端数据 if(recv(client_sockfd,buf,BUFFER_SIZE,0)<0) { perror("recv client data failed"); exit(EXIT_FAILURE); } printf("receive from client:%s/n",buf); // 发送数据到客户端 if(send(client_sockfd,"I have received your message.",BUFFER_SIZE,0)<0) { perror("send failed"); exit(EXIT_FAILURE); } close(client_sockfd); close(server_sockfd); exit(EXIT_SUCCESS); }

       这次,让我们再次反复的启动服务器,尽情的在“黑窗户”里面输入./server ./server ./server ......服务器的程序好像突然间变乖了,呵呵,童鞋们,为自己的成就庆祝吧!!!

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