BUG: LNK2001 on Member Function When Use Nested Class Template (128789)

The information in this article applies to:

Microsoft Visual C++, 32-bit Editions 2.0
Microsoft Visual C++, 32-bit Editions 2.1
Microsoft Visual C++, 32-bit Editions 4.0
Microsoft Visual C++, 32-bit Editions 4.1
Microsoft Visual C++, 32-bit Enterprise Edition 4.2
Microsoft Visual C++, 32-bit Professional Edition 4.2
Microsoft Visual C++, 32-bit Enterprise Edition 5.0
Microsoft Visual C++, 32-bit Professional Edition 5.0
Microsoft Visual C++, 32-bit Enterprise Edition 6.0
Microsoft Visual C++, 32-bit Professional Edition 6.0
Microsoft Visual C++, 32-bit Learning Edition 6.0

This article was previously published under Q128789

SYMPTOMS

When you build a program that uses nested class templates, the following link error is generated:

test.obj: error LNK2001: unresolved external symbol
"?Funtion@BB@?$AA@HH@@QAEHXZ
( public: int __thiscall AA<int,int>::BB::Funtion(void) )"

CAUSE

The compiler does not generate code for the member function in the nested class template.

RESOLUTION

To work around the problem, use one of the following suggestions:

Define the function in the class declaration as an inline function. Be sure to define the function body in the class declaration. Defining the function as an inline function outside the class declaration will not eliminate the problem.

-or-
Use the member function specialization technique to work around the problem. This technique is demonstrated in the "Sample Code" section of this article.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

The following code can be used to reproduce or work around the problem.

Sample Code

   /* Compile options needed: None.
   */ 

   #include <stdio.h>

   template <class T1, class T2>
   class AA
   {
     public:
       class BB
       {
         public:
           int Function();

   // Work around #1, replace the previous line with
   //        int Function() { return 0; }
       };
   };

   // Work around #2, uncomment the following function
   // AA<int,int>::BB::Function()
   // {
   //   return 0;
   // }

   template <class T1, class T2>
   int AA<T1,T2>::BB::Function()
   {
      return 0;
   }

   void main()
   {
     AA<int,int>::BB b;
     printf( "%d\n", b.Function() );
   }

Modification Type:	Minor	Last Reviewed:	7/5/2005
Keywords:	kbBug kbCompiler kbCPPonly kbpending KB128789