FIX: C2670: Template Function Cannot Convert Parameter

The information in this article applies to:

• The Microsoft C/C++ Compiler (CL.EXE) included with: Microsoft Visual C++, 32-bit Edition, version 4.0

SYMPTOMS

The following error is generated:

   error C2670: 'AFunction' : the template function cannot convert
   parameter 1 from type 'class Derived<int> *'

• A template class 'Derived' from another template class 'Base'.
• 'AFunction' taking a pointer to the 'Base' as a parameter.
• A call to the 'AFunction' passing a pointer to 'Derived' before instantiating any object of that type.

RESOLUTION

To work around this problem, either explicitly instantiate 'Derived' or create a dummy object of type 'Derived' before calling the 'AFunction'.

See the Sample Code for an example.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft Visual C++, 32-bit Edition, version 4.1.

MORE INFORMATION

Sample Code

/* Compile options needed: None
*/

   T data;
   int i;

template <class T> class Derived : public Base<T> { public:

   int j;

template <class T>

void AFunction(Base<T>* b)

   return;

void main()

   // Uncomment one of the following two statements to work around the
   // problem. If the template class definition is in a header file,
   // you may want to include one of the following two statements at
   // the end of that file.

   // template Derived<int>;
   // Derived<int> dummy;

   Derived<int> *j;

   AFunction(j);   // Gives C2670 here
}