FIX: C2989 Declaring Template Class in a Namespace

• The C/C++ Compiler (CL.EXE) included with: - Microsoft Visual C++, 32-bit Editions, version 4.2

SYMPTOMS

A template class is defined inside a namespace that has the same name as a non-template class declared at global scope. When you compile this construct, the following error message appears:

   error C2989: '<classname>' : template class has already been defined as
   a non-template class

RESOLUTION

There are 3 ways to work around this problem.

1. Change the name of one of the classes involved. If this is possible, it may be the best solution because having two different classes with the same name could lead to confusion.

2. Move the definition of the non-template class so that it appears after the definition of the template class. See sample code below.

3. Move the definition of the non-template class into a namespace (other than the one the template class is defined in).

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

Sample Code

 /* Compile options needed: none
 */

 class test {}; // Move this line below namespace tester for resolution #2.

 namespace tester {
     template <class T> class test {};
 }