FIX: __vfptr Elements Are Not Properly Displayed in Debugger

• The Integrated Debugger included with: - Microsoft Visual C++, 32-bit Edition, 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
   
   

          [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

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

Keywords          : vcbuglist400 vcfixlist500 WBDebug kbtool
Version           : 4.0 4.1 4.2
Platform          : NT WINDOWS
Issue type        : kbbug
Solution Type     : kbfix