Advantages of Using Window Properties

Window properties are typically used to associate data with a subclassed window or a window in a multiple document interface (MDI) application. In either case, it is not convenient to use the extra bytes specified in the CreateWindow function or class structure for the following two reasons:

• An application might not know how many extra bytes are available or how the space is being used. By using window properties, the application can associate data with a window without accessing the extra bytes.
• An application must access the extra bytes by using offsets. However, window properties are accessed by their string identifiers, not by offsets.

For more information about subclassing, see Window Procedure Subclassing. For more information about MDI windows, see Multiple Document Interface.