FIX: C2065 Error on Functions Returns Template Class By Value (130276)


The information in this article applies to:

  • Microsoft Visual C++, 32-bit Professional Edition 2.0
  • Microsoft Visual C++, 32-bit Professional Edition 2.1
This article was previously published under Q130276

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;}
Modification Type:MinorLast Reviewed:7/5/2005
Keywords:kbbug kbCompiler kbCPPonly kbfix KB130276
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