afx_msg void OnClose();
Called as a signal that the CWnd or an application is to terminate. An application can prompt the user for confirmation and destroy the CWnd object by calling the DestroyWindow member function only if the user confirms the choice.
This message-handler member function calls the Default member function. Override this member function in your derived class to handle the WM_CLOSE message.
CWnd::DestroyWindow, ::PostQuitMessage, WM_CLOSE, CWnd::Default