Microsoft KB Archive/240862

= FIX: C2555 On Virtual Functions with Covariant Return Types =

Article ID: 240862

Article Last Modified on 7/5/2005

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APPLIES TO


 * Microsoft Visual C++ 6.0 Standard Edition
 * Microsoft Visual C++ 6.0 Professional Edition
 * Microsoft Visual C++ 5.0 Professional Edition
 * Microsoft Visual C++ 6.0 Enterprise Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition

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This article was previously published under Q240862



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

Please refer to the sample code in the "More Information" section for details.



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 that this is a bug in the Microsoft products that are listed at the beginning of this article.

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



Steps to Reproduce Behavior
The following sample code demonstrates the error: //test.cpp // compiler option needed: none


 * 1) include "stdafx.h"

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

Keywords: kbbug kbfix kbnoupdate kbcpponly kbcompiler KB240862

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