BUG: C2555 On Virtual Functions with Covariant Return Types

• The C/C++ Compiler (CL.EXE), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

SYMPTOMS

You can receive the following error message if you try to override a virtual function with a covariant return type:

error C2555: 'B::function' : overriding virtual function differs from'A::function' only by return type or calling convention

CAUSE

The compiler does not support virtual functions with covariant return types as specified in the C++ Standard, section 10.3, which is quoted below:

5- The return type of an overriding function shall be either identical to the return type of the overridden function or covariant with the classes of the functions. If a function D::f overrides a function B::f, the return types of the functions are covariant if they satisfy the following criteria:

• both are pointers to classes or references to classes



• the class in the return type of B::f is the same class as the class in the return type of D::f or, is an unambiguous direct or indirect base class of the class in the return type of D::f and is accessible in D



• both pointers or references have the same cv-qualification and the class type in the return type of D::f has the same cv-qualification as or less cv-qualification than the class type in the return type of B::f.

STATUS

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

MORE INFORMATION

Steps to Reproduce Behavior

//test.cpp
// compiler option needed: none

#include "stdafx.h"

class A
     {
      public:
	virtual A* function();
     };
	
class B : public A
     {
      public:
	 B* function();
     };
 

Additional query words:

Keywords : kbCompiler kbCPPonly kbVC kbVC500 kbVC500bug kbVC600 kbVC600bug
Version : winnt:5.0,6.0
Platform : winnt
Issue type : kbbug