Q113417: INFO: C4097: Typedef-Name X Used as Synonym for Class-Name Z

Article: Q113417
Product(s): Microsoft C Compiler
Version(s): 1.0,2.0,2.1,2.2,4.0,4.2,5.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kb
Last Modified: 11-FEB-2002

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 2.2, 4.0, 4.2, 5.0 
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SUMMARY
=======

When a typedef class name is used as a base class, the following warning will
appear if compiled with /Ze (enable Microsoft extensions), which is on by
default:

  warning C4097:Non-standard extension: typedef-name 'identifier1' used as
  synonym for class-name 'identifier2'

If compiled with /Za (disable Microsoft extensions) using Visual C++ for Windows
or Visual C++ 32-bit Edition 1.0, the following error appears:

  error C2505: 'identifier' : is not a legal base class

This error message is correct in accordance with the C++ language specification.
In C++ grammar, the "base-list" is specified as being a list of
"base-specifiers". A base-specifier reduces to a "complete-class-name", which
does not include "typedef-names". Consequently, the compiler is perfectly
correct in generating this warning/error for the sample below.

This error is not generated using Visual C++ 32-bit Edition 2.X. Using Visual C++
32-bit Edition, versions 2.x and above, the compiler generates the following
warning with both the /Ze and /Za switches:

  C4097: typedef-name 'identifier1' used as synonym for class-name
  'identifier2'

MORE INFORMATION
================

For more information on C++ grammar, see the "Grammar Summary" in the "Annotated
C++ Reference Manual" (ARM) by Bjarne Stroustrup and Margaret Ellis (Appendix A)
or Appendix C of the C++ "Language Reference" that comes with Microsoft C/C++
7.0 and Microsoft Visual C++ for Windows, versions 1.0 and 1.5. The same Grammar
Summary is in Appendix A of the "C++ Language Reference" manual for Visual C++
32-bit Edition, versions 1.1 and above, and in the online documentation under
the "Grammar Summary" heading of the "C++ Langauge Reference" included with
Visual C++ 32-bit Edition, version 4.0.

Sample Code
-----------

  /* Compile options needed: /Ze /c /W4
  */ 

   class C
   {
     int _w;
   };

   typedef C D;

   class F : public D     // warning C4097
   { };

   class E : private virtual D // warning C4097
   { };

   class G : protected D // warning C4097
   { };

Additional query words: 8.00 8.00c 9.00 9.10

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Keywords          : kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbvc100 kbVC220 kbVC420 kbVC500 kbVC200 kbVC210 kbVC32bitSearch kbVC500Search
Version           : :1.0,2.0,2.1,2.2,4.0,4.2,5.0
Issue type        : kbinfo

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