WinCE5.0 Socket UDP Multicast例子

要想接收到多播包，必须先加入多播组（224.0.0.1 ~239. 255.255.255）。但是总可以发送多播包，无论加入与否。另外一般的以太网PHY+MAC芯片都有一个Receive Control Register(RCR)，里面可以设置是否接收所有的Multicast包（甚至是Promiscuous模式）还是根据Multicast Table来接收。

接收多播包
-----------------

#include "stdafx.h"
#include <winsock2.h>
#include <ws2tcpip.h>

int MulticastTask()
{
 
 int i = 0;
WSADATA wsaData;
 SOCKET Sock = INVALID_SOCKET;       // Datagram window socket
 struct ip_mreq mreq;                // Used in adding or dropping
  
 struct sockaddr_in sLocalAddr;
 struct sockaddr_in sClientAddr;

 UINT32          lSockAddrSize;

 BYTE buf[100];
 int dataLength;
  
 if (WSAStartup (MAKEWORD(1, 1), &wsaData) != 0)
  return 0;

 // Create a datagram socket, Sock.
 if ((Sock = socket (AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET)
  return 0;

 // Fill out the local socket's address information.
 sLocalAddr.sin_family = AF_INET;
 sLocalAddr.sin_port = htons (3333);
 sLocalAddr.sin_addr.s_addr = htonl (INADDR_ANY);
 
 // Associate the local address with Sock.
 if (bind (Sock,  (struct sockaddr FAR *) &sLocalAddr, sizeof (sLocalAddr)) == SOCKET_ERROR)
 {
  closesocket (Sock);
  return 0;
 }
 
 // Join the multicast group from which to receive datagrams.
 mreq.imr_multiaddr.s_addr = inet_addr ("224.1.1.1"); //
 mreq.imr_interface.s_addr = INADDR_ANY;
 lSockAddrSize = sizeof( struct sockaddr_in );
 
  
 if (setsockopt (Sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char FAR *)&mreq, sizeof (mreq)) == SOCKET_ERROR)
  return 0;

 for (; ;)
 {  
  
  lSockAddrSize = sizeof(sClientAddr);
  memset(&sClientAddr, 0, lSockAddrSize); 
  
  dataLength = recvfrom(Sock, (char*)buf, 100, 0,
   ( struct sockaddr * ) & sClientAddr, &lSockAddrSize);
  
  if (( dataLength == 0 ) || ( dataLength == SOCKET_ERROR ))
   continue;
 }
 
 closesocket (Sock);
 WSACleanup ();
 return 1;
} 

发送多播包(前面与发送基本一样，但不用加入组）
------------------------------------------------------------------------

dest_sin.sin_family = AF_INET;
dest_sin.sin_port = htons (DESTINATION_PORT); 
dest_sin.sin_addr.s_addr = inet_addr (DEST_MCAST);
sendto (Sock, szMessage, strlen (szMessage) + 1, 0, (struct sockaddr FAR *) &dest_sin, sizeof (dest_sin));