While not being very fancy, this application (called ControlPanel) is a small demonstration of how the real Windows Control Panel functions.
When the Control Panel is launched, it looks for .cpl files in the Windows system folder. The .cpl files (called applets) are simple DLLs that export the CPlApplet function. For each applet found, the Control Panel loads that DLL with the ::LoadLibrary function call and then uses the GetProcAddress function to realize a pointer to the CPlApplet function. For each applet, it calls the CPlApplet function by passing it different messages such as CPL_INIT, CPL_INQUIRE etc. You can get help about different messages in the online help of MSDN.
When the Control Panel calls the CPlApplet function with CPL_INQUIRE message, the .cpl file returns a CPLINFO structure which holds information about that perticular applet such as its name, icon, info tip etc. When the Control Panel applet is double-clicked by the user, the CPlApplet function is called with the CPL_DBLCLK value. At this point, the applet generally displays a dialog from which the user can interact with the applet.
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