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

• The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft C/C++ for MS-DOS, versions 7.0, 7.0a - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

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'

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

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
    { };