c++ udp单播,并指定本地发送端口号

 初始化SOCKET：

    //初始化广播Socket
	WSADATA wsdata;
	WSAStartup(MAKEWORD(2, 2), &(wsdata));

	m_socketHmv = socket(AF_INET, SOCK_DGRAM, 0);
	if (m_socketHmv != INVALID_SOCKET)
	{
		BOOL opt = TRUE;
		int optret = setsockopt(m_socketHmv, SOL_SOCKET, SO_BROADCAST, (char* FAR)&opt, sizeof(opt));
		
		//发送addr
		USES_CONVERSION;
		LPCSTR cClirntIp = (LPCSTR)T2A(m_strHmvClientIp);
		memset(&m_addrtoHmv, 0, sizeof(m_addrtoHmv));
		m_addrtoHmv.sin_family = AF_INET;
        //cClirntIp为接收端的IP
		m_addrtoHmv.sin_addr.S_un.S_addr = inet_addr(cClirntIp);
        //cClirntIp为接收端的Port
		m_addrtoHmv.sin_port = htons(m_nUdpPortHmv);

		//本地addr
 		memset(&m_addrLocal, 0, sizeof(m_addrLocal));
 		m_addrLocal.sin_family = AF_INET;
		m_addrLocal.sin_addr.s_addr = htonl(INADDR_ANY);
        //本地port
		m_addrLocal.sin_port = htons(m_nLocalPort);
		
		//设置可以多次绑定
		int nRecvBuf = 1;
		optret = setsockopt(m_socketHmv, SOL_SOCKET, SO_REUSEADDR, (const char*)&nRecvBuf, sizeof(int));

        //绑定本地发送使用端口，这样，本地发送udp消息时，就是从这个端口发送出去的
		if (!bind(m_socketHmv, (sockaddr*)&m_addrLocal, sizeof(m_addrLocal)) != SOCKET_ERROR)
			ASSERT(0); 
	}

发送：

    //根据具体需要构建数据
	int nLength = 200；
	unsigned char* pData = new unsigned char[nLength];
	.......

	if (sendto(m_socketHmv, (char*)pData, nLength, 0, (sockaddr*)&m_addrtoHmv, sizeof(m_addrtoHmv)) == SOCKET_ERROR)
		ASSERT(0);
	delete pData;