A class menu defines the default menu to be used by the windows in the class if no explicit menu is given when the windows are created. A menu is a list of commands from which a user can choose actions for the application to carry out.
You can assign a menu to a class by setting the lpszMenuName member of the WNDCLASSEX structure to the address of a null-terminated string that specifies the resource name of the menu. The menu is assumed to be a resource in the given application. The system automatically loads the menu when it is needed. If the menu resource is identified by an integer and not by a name, the application can set the lpszMenuName member to that integer by applying the MAKEINTRESOURCE macro before assigning the value.
The system does not require a class menu. If an application sets the lpszMenuName member of the WNDCLASSEX structure to NULL, windows in the class have no menu bars. Even if no class menu is given, an application can still define a menu bar for a window when it creates the window.
If a menu is given for a class and a child window of that class is created, the menu is ignored. For more information, see Menus.