Q155164: FIX: C2678 on Overloaded Functions When Using a Namespace

Article: Q155164
Product(s): Microsoft C Compiler
Version(s): 4.0,4.1,4.2
Operating System(s): 
Keyword(s): kbProgramming kbCompiler
Last Modified: 29-NOV-2001

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
- Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
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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
        }

Additional query words:

======================================================================
Keywords          : kbProgramming kbCompiler 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbVC410 kbVC420 kbVC32bitSearch
Version           : :4.0,4.1,4.2
Issue type        : kbbug
Solution Type     : kbfix

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

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