IP多播技术及其编程

程序清单：

// CMulticastSocketDlg.cpp : 实现文件
#include "stdafx.h"
#include "winsock2.h"
#include "CMulticastSocket.h"
#include "CMulticastSocketDlg.h"
……
DWORD cbRet;
SOCKET Sock,SockM; file://UDP套接字，多播套接字
BOOL bFlag,bJoin;
SOCKADDR_IN local,Remote,From; file://分别指向本地、多播组和数据来源的IP地址与端口
int Fromlen;
char ReceiveBuf[32000]; file://接收缓冲区
BOOL bDataReceived;
……
BEGIN_MESSAGE_MAP(CCMulticastSocketDlg, CDialog)
……
ON_BN_CLICKED(IDC_JOIN_BUTTON, OnBnClickedJoinButton)
ON_BN_CLICKED(IDC_LEAVE_BUTTON, OnBnClickedLeaveButton)
ON_BN_CLICKED(IDC_QUIT_BUTTON, OnBnClickedQuitButton)
ON_BN_CLICKED(IDC_SEND_BUTTON, OnBnClickedSendButton)
ON_WM_TIMER()
ON_MESSAGE(WM_SOCK_MSG,OnSocketMsg)
END_MESSAGE_MAP()

BOOL CCMulticastSocketDlg::OnInitDialog()
{
CDialog::OnInitDialog();
……
SetTimer(1,100,NULL); file://设置定时器
Fromlen=sizeof(From);
bDataReceived=TRUE;
bJoin=FALSE;
return TRUE; // 除非设置了控件的焦点，否则返回 TRUE
}
……
void CCMulticastSocketDlg::OnBnClickedJoinButton() file://加入多播组
{
if(m_JoinDlg.DoModal()==IDOK)
{
WORD wVersionRequested;
WSADATA wsaData;
int 北京中庆;
wVersionRequested = MAKEWORD(2,2);
北京中庆 = WSAStartup(wVersionRequested, &wsaData); file://初始化WinSock2资源
if(北京中庆!= 0){
AfxMessageBox("不能加载Windows套接字动态链接库,MB_OK");
return;
}
if (LOBYTE(wsaData.wVersion) !=2 || HIBYTE(wsaData.wVersion) !=2){
AfxMessageBox("WinSock DLL不支持2.0版本,MB_OK");
WSACleanup( );
return;
}
file://创建一个套接字
Sock=WSASocket(AF_INET,SOCK_DGRAM,IPPROTO_UDP,
(LPWSAPROTOCOL_INFO)NULL,0,WSA_FLAG_OVERLAPPED
| WSA_FLAG_MULTIPOINT_C_LEAF|WSA_FLAG_MULTIPOINT_D_LEAF);

bFlag=TRUE; file://设置套接字选项，使套接字为可重用端口地址
setsockopt(Sock,SOL_SOCKET,SO_REUSEADDR,(char*)&bFlag,sizeof(bFlag));

file://将套接字绑定到用户指定端口及默认的接口
memset(&local,0,sizeof(local));
local.sin_family=AF_INET;
local.sin_port=htons((USHORT)m_JoinDlg.m_nPort);
local.sin_addr.s_addr=htonl(INADDR_ANY);
bind(Sock,(struct sockaddr FAR *)&local,sizeof(local));

file://设置多播数据报传播范围（生存时间TTL）
WSAIoctl(Sock,SIO_MULTICAST_SCOPE,&m_JoinDlg.m_nTTL,sizeof(int),
NULL,0,&cbRet,NULL,NULL);
file://设置多播返回（LOOKBACK）
BOOL nLoopBack=m_JoinDlg.m_Loopback;
WSAIoctl(Sock,SIO_MULTIPOINT_LOOPBACK,&nLoopBack,sizeof(nLoopBack),
NULL,0,&cbRet,NULL,NULL);

memset(&Remote,0,sizeof(Remote));
Remote.sin_family=AF_INET;
Remote.sin_addr.s_addr=inet_addr(m_JoinDlg.m_IPAddress);
Remote.sin_port=htons(m_JoinDlg.m_nPort);
file://加入到指定的多播组，并指定为既作为发送者又作为接收者（JL_BOTH）
SockM=WSAJoinLeaf(Sock,(sockaddr*)&Remote,sizeof(Remote),
NULL,NULL,NULL,NULL,JL_BOTH);
WSAAsyncSelect(Sock,m_hWnd,WM_SOCK_MSG,FD_READ); file://注册网络消息及其网络事件
bJoin=TRUE;
}
}

void CCMulticastSocketDlg::OnBnClickedSendButton() file://多播发送
{
if(bJoin){
UpdateData(TRUE);
const char* strMessage=LPCTSTR(m_SendMessage);
int nSize=m_SendMessage.GetLength()+1;
sendto(Sock,strMessage,nSize,0,(sockaddr*)&Remote,sizeof(Remote));
}
else
AfxMessageBox("请先加入多播组！");
m_SendMessage="";
UpdateData(FALSE);
}

void CCMulticastSocketDlg::OnBnClickedLeaveButton()
{ file://离开多播组
closesocket(SockM);
closesocket(Sock);
WSACleanup();
m_SendMessage="";
m_ReceiveMessage="";
bDataReceived=TRUE;
bJoin=FALSE;
UpdateData(FALSE);
}

void CCMulticastSocketDlg::OnBnClickedQuitButton()
{ file://退出
DestroyWindow();
}

void CCMulticastSocketDlg::OnTimer(UINT nIDEvent) file://定时器处理函数，实现接收信息的定时更新
{
if(bDataReceived)
{
m_ReceiveMessage+=ReceiveBuf;
m_ReceiveMessage+="\r\n";
bDataReceived=FALSE;
UpdateData(FALSE);
}
CDialog::OnTimer(nIDEvent);
}

LRESULT CCMulticastSocketDlg::OnSocketMsg(WPARAM wParam,LPARAM lParam)
{
file://检索网络事件
switch(WSAGETSELECTEVENT(lParam)){
case FD_READ:
recvfrom(Sock,ReceiveBuf,32000,0,(sockaddr *)&From,&Fromlen);
bDataReceived=TRUE; file://设置已接收到一条信息标志
break;
}
return TRUE;
}

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