FIX: C2555 with Virtual Function Returning Template Object (184089)

The information in this article applies to:

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

This article was previously published under Q184089

SYMPTOMS

A virtual function returning a templated class object and a derived class defining the virtual function, causes the following compiler error:

error C2555: 'MyDerived::TestFunc' : overriding virtual function differs from 'MyBase::TestFunc' only by return type or calling convention

RESOLUTION

Define the base class function to be nonvirtual.

STATUS

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

This problem was corrected in Microsoft Visual C++ .NET.

MORE INFORMATION

Sample Code

template <class T>
   class TestClass
   {
      public:
         T val;
         TestClass(T num){val=num;}

   };

   class MyBase
   {
     public:
       int value;
       virtual TestClass<float> TestFunc(void) ;
       /* Make this function nonvirtual to fix C2555 error. */ 
       /* A pure virtual function also has the same problem. */ 
   };
   template <class T>
   class MyDerived : public MyBase
   {
     public:
       virtual TestClass<float> TestFunc(void)
       {
         return TestClass<float>(3.14f);
       }
   };
   MyDerived<int> x;
   void main(void)
   {
     x.TestFunc();
   }

REFERENCES

Modification Type:	Major	Last Reviewed:	12/8/2003
Keywords:	kbBug kbCompiler kbCPPonly kbfix kbLangCPP kbNoUpdate KB184089