DOCUMENT:Q155164  29-NOV-2001  [visualc]
TITLE   :FIX: C2678 on Overloaded Functions When Using a Namespace
PRODUCT :Microsoft C Compiler
PROD/VER::4.0,4.1,4.2
OPER/SYS:
KEYWORDS:kbProgramming kbCompiler

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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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