In MFC-land, you don’t normally call RegisterClass because MFC registers several window classes for you, such as AfxFrameOrView and others with weird names like Afx:400000:3:1:14fe:10:0.
You can also change the style by calling SetClassLong(GCL_STYLE), but you might confuse MFC because it encodes the style as part of the class name (the 400000 in the example above).
//#32768 The class for a menu.
//#32769 The class for the desktop window.
//#32770 The class for a dialog box.
//#32771 The class for the task switch window.
//#32772 The class for icon titles.