FIX: C2678 on Overloaded Functions When Using a Namespace

Last reviewed: September 19, 1997
Article ID: Q155164
The information in this article applies to:
  • The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft Visual C++, 32-bit Edition, versions 4.0, 4.1, 4.2

SYMPTOMS

The wrong version of an overloaded function is called causing the following compiler two errors:

   error C2678: binary '!=' : no operator defined which takes a left-hand
   operand of type 'const struct Test' (or there is no acceptable
   conversion) (new behavior; please see help)

   error C2664: 'Tester' : cannot convert parameter 1 from 'const struct
   Test' to 'const float &' (new behavior; please see help)

The sample in the “Sample Code” demonstrates this problem. These errors occur when:

  1. The function has a global definition.

  2. The function (with the same name and different argument types compared to the global function) is defined in a named namespace.

  3. The named Namespace function is included in the global namespace by the “using” declarative.

RESOLUTION

  1. Put the function in a named namespace (within the global namespace) and then use the “using” declaration. See workaround #1 below.

  2. Specify the “using” declaration at the global level. See workaround #2 below.

Also see the "More Information" section for the sample code and the workarounds.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ version 5.0.

MORE INFORMATION

The following sample code demonstrates the problem of incorrect overloaded function call causing the C2678 and the C2664 compiler errors.

Sample Code

/* Compile options needed: none
*/
      struct Test
      {
      } ;
// Uncomment the following 2 lines for workaround #1
//      namespace Space2
//      {
          int Tester(const Test& rx, const Test& ry)
          {
             return 0 ;
          }

          int operator!=(const Test& rx, const Test& ry)
          {
             return 0 ;
          }
// Uncomment the following line for workaround #1
//      }

      namespace Space1
      {
         int operator!=(const float& rx, const Test& rt)
         {
             return 1 ;
         }

         int Tester(const float& rx, const int& ri)
         {
             return 1 ;
         }
      }

// Uncomment the following line for workaround #2
//      using namespace Space1 ;
      void main()
      {
         const Test a ;
         const Test b ;
         using namespace Space1 ;
         if (a != b) ;  // This line causes the C2678
         Tester(a, b);  // This line causes the C2664
      }
Keywords          : CLIss kbprg
Version           : 4.0 4.1 4.2
Platform          : NT WINDOWS
Issue type        : kbbug
Solution Type     : kbfix


================================================================================


THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last reviewed: September 19, 1997
© 1998 Microsoft Corporation. All rights reserved. Terms of Use.