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Q150003: FIX: __vfptr Elements Are Not Properly Displayed in Debugger

Article: Q150003
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbDebug kbide kbVC500fix
Last Modified: 31-JUL-2001

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

- The Integrated Debugger, used with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 4.0, 4.1, 4.2 
-------------------------------------------------------------------------------

SYMPTOMS
========

When you view the theApp variable in an AppWizard-generated MFC application, the
element values of __vfptr are not properly displayed in the debugger. For an
example, please see the "More Information" section of this article.

RESOLUTION
==========

Drag the address of __vfptr into the memory window, view the data in long-hex
format, and notice that the addresses to which the __vfptr variable points
appear.

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 Visual C++ version 5.0.

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

Example
-------

1. Create a default AppWizard MFC application. In the InitInstance(), view the
  theApp variable in the watch window.

2. Expand the theApp variable to view the following tree structure:

     theApp
      CWinApp
       CWinThread
        CCmdTarget
         CObject
           __vfptr = 0x00405118   // This is correct

Under Windows NT:

            [0] CXX0030: Error: expression cannot be evaluated
            [1] CXX0030: Error: expression cannot be evaluated
            [2] CXX0030: Error: expression cannot be evaluated
            [3] CXX0030: Error: expression cannot be evaluated
            [4] CXX0030: Error: expression cannot be evaluated

Under Windows 95 (All values are incorrect):

            [0] 0xf000e681
            [1] 0xf000ff47
            [2] 0xf000ff47
            [3] 0xf000ff47
            [4] 0xf000ff47

Additional query words: kbVC400bug

======================================================================
Keywords          : kbDebug kbide kbVC500fix 
Technology        : kbVCsearch kbAudDeveloper kbIntegratedDebugger
Version           : winnt:
Issue type        : kbbug
Solution Type     : kbfix

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

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