FIX: C2676 on Overloaded Operators of Templated Classes (130370)


The information in this article applies to:

  • Microsoft Visual C++
This article was previously published under Q130370

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
}
Modification Type:MinorLast Reviewed:7/5/2005
Keywords:kbbug kbCompiler kbCPPonly kbfix KB130370
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