Provides the base functionality of all window classes in the Microsoft Foundation Class Library.
A CWnd object is distinct from a Windows window, but the two are tightly linked. A CWnd object is created or destroyed by the CWnd constructor and destructor. The Windows window, on the other hand, is a data structure internal to Windows that is created by a Create member function and destroyed by the CWnd virtual destructor. The DestroyWindow function destroys the Windows window without destroying the object.
The CWnd class and the message-map mechanism hide the WndProc function. Incoming Windows notification messages are automatically routed through the message map to the proper OnMessage CWnd member functions. You override an OnMessage member function to handle a member's particular message in your derived classes.
The CWnd class also lets you create a Windows child window for your application. Derive a class from CWnd, then add member variables to the derived class to store data specific to your application. Implement message-handler member functions and a message map in the derived class to specify what happens when messages are directed to the window.
You create a child window in two steps. First, call the constructor CWnd to construct the CWnd object, then call the Create member function to create the child window and attach it to the CWnd object.
When the user terminates your child window, destroy the CWnd object, or call the DestroyWindow member function to remove the window and destroy its data structures.
Within the Microsoft Foundation Class Library, further classes are derived from CWnd to provide specific window types. Many of these classes, including CFrameWnd, CMDIFrameWnd, CMDIChildWnd, CView, and CDialog, are designed for further derivation. The control classes derived from CWnd, such as CButton, can be used directly or can be used for further derivation of classes.