// "待ち受け"ボタン押下
void CServerSockDlg::OnBnClickedBtnListen()
{
    CSocket         sock, conSock;
    unsigned int    port = 0;
    CString         sendStr, recvStr;
    int             send, recv, sendSum, recvSum;
    LPCSTR          byteCP = NULL;
    LPSTR           byteP = NULL;
    int             err = 0;
    
    UpdateData();
    
    // (1)ポート取得
    if (!err) if (_stscanf_s(m_xvEditPort, _T("%d"), &port) != 1) err = 1;
    // (2)ソケット作成
    if (!err) if (!sock.Create(port)) err = 1;
    // (3)接続要求を待機
    if (!err) if (!sock.Listen(1)) err = 1;
    // (4)接続受け入れ
    if (!err) if (!sock.Accept(conSock)) err = 1;
    // (5)受信(20バイト固定)
    if (!err)
    {
        byteP = recvStr.GetBuffer(21);
        recvSum = 0;
        while (recvSum < 20)
        {
            recv = conSock.Receive(byteP +recvSum, 20 -recvSum);
            if (recv == SOCKET_ERROR || recv == 0) {err = 1; break;}
            recvSum += recv;
        }
        byteP[20] = '\0';
        recvStr.ReleaseBuffer();
    }
    if (!err)
    {
        m_xvEditLog += _T("Recv : ");
        m_xvEditLog += recvStr +_T("\r\n");
    }
    // (6)送信(20バイト固定)
    if (!err)
    {
        sendStr = _T("Welcome!");
        while (sendStr.GetLength() < 20) sendStr += _T(" ");
        
        sendSum = 0;
        while (sendSum < 20)
        {
            byteCP = static_cast<LPCSTR>(sendStr) +sendSum;
            send = conSock.Send(byteCP, 20 -sendSum);
            if (send == SOCKET_ERROR) {err = 1; break;}
            sendSum += send;
        }
    }
    if (!err)
    {
        m_xvEditLog += _T("Send : ");
        m_xvEditLog += sendStr +_T("\r\n");
    }
    // (7)エラー表示
    if (err)
    {
        LPVOID        lpMsgBuf = NULL;

        ::FormatMessage(
            FORMAT_MESSAGE_ALLOCATE_BUFFER |
            FORMAT_MESSAGE_FROM_SYSTEM |
            FORMAT_MESSAGE_IGNORE_INSERTS,
            NULL, sock.GetLastError(),
            MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
            (LPTSTR)&lpMsgBuf, 0, NULL);

        m_xvEditLog += _T("Error : ");
        m_xvEditLog += static_cast<LPTSTR>(lpMsgBuf);
        LocalFree(lpMsgBuf);
    }
    // (8)切断
    conSock.Close();
    sock.Close();
    UpdateData(FALSE);
    
    return;
}