Q130370: FIX: C2676 on Overloaded Operators of Templated Classes

Article: Q130370
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVCkbbuglist kbfixlist
Last Modified: 23-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++ 
-------------------------------------------------------------------------------

SYMPTOMS
========

When a templated class is not instantiated, but its member operators are
referenced, the following error is generated:

  error C2676: [binary/unary] '<op>' : 'class [ClassName]<temp
  type>' does not define this operator or a conversion to a type acceptable
  to the predefined operator.

NOTE: The line number referenced by the error message refers to the point where
the operator is referenced (called), not the operator's definition.

RESOLUTION
==========

The template class must be instantiated for the particular data type being
referenced (< class T> below). This instantiation can be accomplished in
one of two ways:

- Instantiate the class prior to referencing any of its operator functions. Any
  of the following three statements will instantiate the class and prevent the
  problem:

        TmpltClass<type> X;        // declare a global instance of the class
        extern TmpltClass<type> X; // X must be a global defined elsewhere
        template TmpltClass<type>; // explicit instantiation

  NOTE: Explicit instantiation works only if the template class and all of its
  member functions are fully defined.

-or-

- For each overloaded operator referenced, replace the first reference to that
  operator with the function form of the operator. For example, replace "X + Y"
  with "X.operator+(Y)" (NOTE: Only the first reference needs to be replaced
  with the function form.)

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem was fixed in Microsoft Visual C++,
32-bit Edition, version 4.0.

MORE INFORMATION
================

In the sample code below, the "*" operator has been chosen to reproduce the
problem, but the problem occurs with both binary and unary (prefix or postfix)
operators. In all cases, the workarounds are the same. The return type of the
operator function has no bearing on the problem.

NOTE: If the operator is the function call operator (), the error is C2604
instead of C2676, but the workarounds are the same.

Sample Code
-----------

  /* Compile Options Needed: None
  */ 

  template< class T > class TmpltClass
  {
       T X;
     public:
       T& operator*(int Arg1) {return X;}
  };

  // Workaround 1: uncomment any one of the following three lines:
  // TmpltClass<int> X;
  // extern TmpltClass<int> X;
  // template TmpltClass<int>;

  void test(TmpltClass<int>& theArg)
  {
  // Workaround 2: uncomment the next line:
  //   theArg.operator*(0);
     theArg * 0;  //do not comment out this line
  }

Additional query words: 2.00 2.10 2.20 9.00 9.10

======================================================================
Keywords          : kbCompiler kbCPPonly kbVC kbbuglist kbfixlist
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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