ExitInstance Member Function
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The ExitInstance member function of class CWinApp is called each time a copy of your application terminates, usually as a result of the user quitting the application.
Override ExitInstance if you need special cleanup processing, such as freeing graphics device interface (GDI) resources or deallocating memory used during program execution. Cleanup of standard items such as documents and views, however, is provided by the framework, with other overridable functions for doing special cleanup specific to those objects.