BUG: LNK2001 on Member Function When Use Nested Class Template
Last reviewed: July 24, 1997
Article ID: Q128789
The information in this article applies to:
The Microsoft C/C++ Compiler (CL.EXE) included with: - Microsoft Visual C++, 32-bit Edition, versions 2.0, 2.1, 4.0, 4.1,
4.2, 5.0
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. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.
MORE INFORMATION
The following code can be used to reproduce or work around the problem.
Code:
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() );
}