VC CreateWindow 找不到窗口类，有提示是因为没有调用RegisterClass注册窗口类，可是我已经使用RegisterClassEx注册了！
//函数：MyRegisterClass
//作用：注册窗口类

ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEX wndclass;
wndclass.cbSize = sizeof(wndclass);
wndclass.style = CS_HREDRAW | CS_VREDRAW;
wndclass.lpfnWndProc = WndProc;
wndclass.cbClsExtra = 0;
wndclass.cbWndExtra = 0;
wndclass.hInstance = hInstance;
wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
wndclass.lpszMenuName = NULL;
wndclass.lpszClassName = szAppName;
return RegisterClassEx(&wndclass);
}

后来改为使用RegisterClass问题解决了：
//函数：MyRegisterClass
//作用：注册窗口类

ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASS wndclass;
    //wndclass.cbSize = sizeof(wndclass);
    wndclass.style = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc = WndProc;
    wndclass.cbClsExtra = 0;
    wndclass.cbWndExtra = 0;
    wndclass.hInstance = hInstance;
    wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName = NULL;
    wndclass.lpszClassName = szAppName;
    return RegisterClass(&wndclass);
}