The single characteristic that sets the Microsoft Foundation Class (MFC) Library apart from other class libraries for Windows is the very close mapping to the Windows API written in the C language. Further, you can generally mix calls to the class library freely with direct calls to the Windows API. This direct access does not, however, imply that the classes are a complete replacement for that API. Developers must still occasionally make direct calls to some Windows functions, such as SetCursor and GetSystemMetrics, for example. A Windows function is wrapped by a class member function only when there is a clear advantage to doing so.
Because you sometimes need to make native Windows function calls, you should have access to the C-language Windows API documentation. This documentation is included with Microsoft Visual C++.
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For an overview of how the MFC Library framework operates, see Using the Classes to Write Applications for Windows.