FIX: C2676 on Overloaded Operators of Templated Classes

• 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.

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
Version : winnt:
Platform : winnt
Issue type :