Q243351: BUG: /Za Compiler Option Causes C2248 Compiler Error

Article: Q243351
Product(s): Microsoft C Compiler
Version(s): winnt:6.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC600 kbVC600bug
Last Modified: 03-MAY-2001

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

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When compiling code with the /Za compiler option (Disable Microsoft Language
extensions) you may get the following error:

  error C2248: 'member' : cannot access private 'member' declared in class
  'class'

For details, please look in the "More Information" section.

CAUSE
=====

The compiler is unable to defer the access checking until it determines the use
of a private member as a return type. The C++ Standard, Section 11 Paragraph 5
states the following:

"The access control for names used in the definition of a class member that
appears outside of the member's class definition is done as if the entire member
definition appeared in the scope of the member's class. In particular, access
controls apply as usual to member names accessed as part of a function return
type, even though it is not possible to determine the access privileges of that
use without first parsing the rest of the function declarator."

RESOLUTION
==========

There are two workarounds for this problem.

1. Define the private function within the class definition itself.

2. Define a public typedef for the return type.

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
---------------------------

To reproduce the problem, compile the following piece of code with the /Za
option.

  //compiler options : cl /Za

  // #define WORKAROUND 
  // Uncomment the above line for workaround 2.

  class A
  {
  private :
  	struct inner {};
  	inner PrivFunc();

  public:
      A(){}

  #ifdef WORKAROUND
  		typedef inner INNER; 
  #endif
  		

  };

  #ifndef WORKAROUND
  A::inner A::PrivFunc()
  {
  	return inner();
  }
  #else
  A::INNER A::PrivFunc()
  {
  	return INNER();
  }
  #endif

  void main(void)
  {

  }

The use of A::inner is well formed here because A::inner is a member of class A.
This implies that the access checking for the first use of A::inner must be
deferred until it is determined that this use of A::inner is as the return type
of a member of class A.

Additional query words:

======================================================================
Keywords          : kbCompiler kbCPPonly kbVC600 kbVC600bug 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : winnt:6.0
Issue type        : kbbug

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

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.