MFC中单文档中WSAAsyncSelect参数问题！懂者，望来请教（虽然分不多。。。。）

C/C++ code

int  CFiveQiView::Login(){    CEnter    userenter;    userenter.DoModal();    CView* pView=(CView*)((CFrameWnd*)AfxGetApp()-> m_pMainWnd)-> GetActiveView(); [color=#FF00FF]//这里出错（CFrameWnd*)AfxGetApp()-> m_pMainWnd是空的？？如何纠正[/color]             WSADATA wsd;    if (WSAStartup(MAKEWORD(2,2),&wsd)!=0)    {        AfxMessageBox(_T("动态库套接字初始化失败"));        return 0;    }    if ((m_socket=socket(AF_INET,SOCK_DGRAM,0))==INVALID_SOCKET)    {        AfxMessageBox(_T("套接字创建失败！"));        WSACleanup();        return 0;    }    //--------------------------获取本机（CString类型）IP-----------------------------------    PHOSTENT hostinfo;    char name[200];    CString IP;    if (gethostname(name,sizeof(name))==0)//获取主机名    {        if ((hostinfo=gethostbyname(name))!=NULL)//通过主机名获取本地IP        {            IP=inet_ntoa(*(struct in_addr*)*hostinfo->h_addr_list);//将获取的IP转换为字符串        }    }    //---------------------------绑定套接字-----------------------------------------------------    SOCKADDR_IN serverAddr;    char *serverIP = new char[20];    WideCharToMultiByte(CP_ACP,0,IP.GetBuffer(),-1,serverIP,20,NULL,NULL);//Unicode转换成多字节字符串    serverAddr.sin_family=AF_INET;    serverAddr.sin_port=htons(5050);    serverAddr.sin_addr.S_un.S_addr=inet_addr(serverIP);//此处的inet_addr()里的参数需要的是多字节里的CString类型或Unicode里的char *类型，故上面用到WideCharToMultiByte    if(bind(m_socket,(SOCKADDR *)&serverAddr,sizeof(serverAddr))==SOCKET_ERROR)    {        AfxMessageBox(_T("绑定IP失败！"));        closesocket(m_socket);        WSACleanup();    }    if (WSAAsyncSelect(m_socket,pView->GetSafeHwnd(),UM_SOCK,FD_READ)==SOCKET_ERROR[color=#FF00FF])//这里第二个参数该填什么[/color]             {        AfxMessageBox(_T("失败！"));        closesocket(m_socket);        WSACleanup();        return 0;    }}