如何判断SOCKET还是连接着的

转自 http://blog.csdn.net/loadstar_kun/article/details/5790407

1. 用read函数来判断

 

读到长度0不能断定是已经断开.除非是-1,才代表输入流已经被关闭,说名socket已经close,而且关键在于你怎么读,实际上应该是一个单独的线程一直在读,因为你无法预先知道能不能一次将发过来的包读完,也无法知道一次是不是读完整了包,所以线称一直循环在读并且一直在解包.这样即能知道什么时候server断,也完成了消息的解读,我的方案是这样的,在大数据量高速率网络上运行没有发生过丢包

 

// 判断是否连接

char ch = 'A';

if (read(g_sockfd, &ch, 1)<=0)

{

if (connect(g_sockfd,(struct sockaddr*)&g_serv_addr, sizeof(g_serv_addr) ) == 0)

        {

                  ServiceLog.write_log("[NotifyDAU]:connect to DAU  success.");

        }

         else

         {

                   ServiceLog.write_log("[NotifyDAU]:can't connect to DAU ");

                   return;

         }

}

 

用try{}catch{}是比较合适。

 

当他是连着的，当进行通讯时发生异常后就知道了.

当你不断的read的时候,server断,exception就catch到了。

 

2. 心跳包

可不可以在Client设一个定时器，每隔一段时间发一条消息给服务器，看能不能收到服务器的响应。

心跳包就是定时发包，没回应就判断断开。

 

3. getsockopt

int optval, optlen = sizeof(int);

getsockopt(sd, SOL_SOCKET, SO_ERROR,(char*) &optval, &optlen);

switch(optval){

      case 0:

        //“处于连接状态“          

        break;    

      case ECONNREFUSED:

      case EHOSTNUMREACH:

}

 

4. 项目中使用的情况

// 判断是否连接

int optval, optlen = sizeof(int);

int r = getsockopt(g_sockfd, SOL_SOCKET, SO_ERROR,(char*) &optval, &optlen);

// send HELLO 包

if ((optval == 0) && (r == 0) && (send(g_sockfd,(char*)&g_DAUCommand,sizeof(struct _DAUCommand),0) != SOCKET_ERROR ))

{

ServiceLog.write_log("[threadOperationWaitTrasferAgain]: try to recv from dau...");

         length = recv(g_sockfd,(char *)&command,sizeof(struct _DAUCommand),0);

}

else

{

         if (connect(g_sockfd,(struct sockaddr*)&g_serv_addr, sizeof(g_serv_addr) ) == 0)

         {

                  ServiceLog.write_log("[threadOperationWaitTrasferAgain]:connect to DAU  success.");

                   ServiceLog.write_log("[threadOperationWaitTrasferAgain]: try to recv from dau...");

                   length = recv(g_sockfd,(char *)&command,sizeof(struct _DAUCommand),0);

         }

         else

         {

                   ServiceLog.write_log("[threadOperationWaitTransferAgain]:can't connect to DAU, try again ");

                   length = 0;

                   continue;

         }

}