在Qt 4.8中QtNetwork—>QUdpSocket类中新增加了“joinMulticastGroup”函数，可以让QUdpSocket加入指定的多播组，来监听来自改组的消息。

例子：

1. QUdpsocket *socket;
2.     QHostAddress mcast_addr("224.0.0.17"); 
3.  
4.     /* New socket */
   
5.     socket = new QUdpSocket(this);
   
6. 
   
7.     /* Binding to a port */
   
8.     if (!socket->bind(port, QUdpSocket::ShareAddress)){
   
9.         qErrnoWarning("Binding error!");
   
10.         exit(1);
    
11.     }
    
12. 
    
13. #ifdef MCAST_IMPLEMENT
    
14.     /* Set socket option disable multicast loopback */
    
15.     socket->setSocketOption(QAbstractSocket::MulticastLoopbackOption, 0);
    
16. 
    
17.     /* Join to a multicast group */
    
18.     if (!socket->joinMulticastGroup(mcast_addr)){
    
19.         qErrnoWarning("Join to multicast group error!");
    
20.         exit(2);
    
21.     }
    
22. #endif