1. Conventional DLLs can be called by various programs, and extended DLLs can only be called by MFC programs. Control classes provided for external use can only be extended with DLLs.
2. The entry function of the extended DLL is DllMain(), which can only be called by a vc++ program (MFC program), while the regular DLL entry is a class inherited from CWinApp, without a message loop.
3. Conventional DLLs can only export C++ classes, functions, and variables, but extended DLLs can export mfc classes (that is, classes that inherit from mfc), C++ classes, functions, and variables.
4. Extending the mfc export class is generally useful macro AFX_EXT_CLASS
4. Remember that only MFC extension DLLs can make parameters and return values use MFC data types
For specific differences, please refer to: https://blog.csdn.net/qing666888/article/details/50720827
For the difference in writing, please refer to: https://blog.csdn.net/m372897500/article/details/7246418