FIX: C2678 on Overloaded Functions When Using a Namespace (155164)


The information in this article applies to:

  • Microsoft Visual C++, 32-bit Editions 4.0
  • Microsoft Visual C++, 32-bit Editions 4.1
  • Microsoft Visual C++, 32-bit Enterprise Edition 4.2
  • Microsoft Visual C++, 32-bit Professional Edition 4.2
This article was previously published under Q155164

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)
-and- 
   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
      }
Modification Type:MajorLast Reviewed:12/1/2003
Keywords:kbbug kbCompiler kbfix kbProgramming KB155164
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