FIX: C2065 Error on Functions Returns Template Class By Value

ID: Q130276

The information in this article applies to:

The C/C++ Compiler (CL.EXE), included with:
- Microsoft Visual C++ 32-bit Edition, versions 2.0, 2.1

SYMPTOMS

Any reference to a template function that returns a template class by value generates these errors:

error C2065: 'function name' : undeclared identifier

error C2064: term does not evaluate to a function C2065

RESOLUTION

Modify the function to return a reference to the template class instead of returning by value. In the "Sample Code" section of this article, function 'f1' returns a template class by value and fails. Function 'f2' returns a template class by reference and succeeds.

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

Sample Code


/* Compile options required: none
*/ 
template<class T>
class M {
public:
   T m;
};

template<class T>
M<T> f1(const M<T>& x) {return x;}

template<class T>
M<T>& f2(const M<T>& x) {return x;}

void test(void)
{
   M<int> x;
   M<int> y = f1(x);  // errors C2065 & C2064
   M<int> z = f2(x);  // no error
}

NOTE: Although this has been fixed under Visual C++ 4.0, the definition of function f2:


   template<class T>
   M<T>& f2(const M<T>& x) {return x;}

causes the following compilation errors:

error C2446: [*] 'return' : no conversion from 'const class M<int>' to 'class M<int> &' (new behavior; please see help)

error C2561: 'f2' : function must return a value

To avoid this, the return value of that statement should be casted appropriately, as follows:


   M<T>& f2(const M<T>& x) {return (M<T>&)x;}

Additional query words: 2.00 2.10 9.00 9.10

Keywords : kbCompiler kbCPPonly kbVC
Version : winnt:
Platform : winnt
Issue type :