Q151168: FIX: Abstract Class Instantiated as a Temporary Object

Article: Q151168
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbLangCPP kbVCkbbuglist kbfixlist
Last Modified: 30-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The Standard C++ Library, included with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

In certain cases, Visual C++ allows abstract classes to be instantiated as
temporary objects. The sample code below demonstrates this.

CAUSE
=====

An abstract class should not be allowed to be instantiated as an object. An
abstract class is any class with at least one pure virtual function. This is
part of the definition of the C++ language.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug was corrected in Microsoft Visual C++,
32-bit Edition, version 4.1.

MORE INFORMATION
================

Sample Code
-----------

     /* Compile options needed: /c /GX
     */ 

  class Exception    //abstract class
  {

     /* Compile options needed: /c /GX
     */ 

     class Exception    //abstract class
     {
         int m_nCause;
         char * m_pszMsg;
     public:
         Exception();
         Exception( int, const char * = 0);
         Exception( const Exception &);
         ~Exception();
         inline virtual int Cause() = 0;           //pure virtual function
         inline virtual const char * Msg() = 0;    //pure virtual function
     };

     int Exception::Cause()
     {
         return m_nCause;
     }

     const char * Exception::Msg()
     {
         return m_pszMsg;
     }

     void main()
     {
         try
         {
             int r = Exception(55,"no error").Cause();    //should be an
     ERROR
             throw Exception(-1,"error");                 //should be an
     ERROR
         }
         catch (Exception&e)
         {
         }
     }

Additional query words: 4.00

======================================================================
Keywords          : kbCompiler kbCPPonly kbLangCPP kbVC kbbuglist kbfixlist
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.