This first occurs when you want to locate the error in the program, and if there is no problem, look at the declaration and definition of the class carefully. It is possible that the corresponding class is not added later;
The second reason is that you may have forgotten to add the header file "StdAfx", if so you can add #include "stdafx" try.
The third reason is that a function declared in a class may be defined without the addition of a class name. Therefore, you must add the class name when you declare a function definition in a class, or you will get this type of error
The fourth reason is that there may be some superfluous symbols, such as "/" or "more" in the program, which can occur. In the author's program, there have been similar problems, carefully examined for a long time to find, vs hints that the wrong place is sometimes inconsistent with the real error.
Summary of MFC "Missing function title (whether it is an old-fashioned form table)"