The ObjectARX SDK provides two simple C++ classes that can be used to make resource management easier. The CAcExtensionModule class serves two purposes—it provides a placeholder for an AFX_EXTENSION_MODULE structure (normally used to initialize or terminate an MFC extension DLL) and tracks two resource providers for the DLL. The resource providers are the module's resources (which are normally the DLL itself, but may be set to some other module) and the default resources (normally the host application, but are actually the provider currently active when AttachInstance() is called). CAcExtensionModule tracks these to simplify switching MFC resource lookup between the default and the module's. A DLL should create one instance of this class and provide the implementation for the class.