socket编程——组播

1、发送：

//设置组播ttl的值，默认为1
int ttl = 1;
setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&ttl, sizeof(ttl)); 

2、接收：

// 加入组播啦  
ip_mreq multiCast;  
multiCast.imr_interface.S_un.S_addr = INADDR_ANY;  
multiCast.imr_multiaddr.S_un.S_addr = inet_addr("234.2.2.2");  
setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&multiCast, sizeof(multiCast));