Q168111: FIX: #import Does Not Compensate for Gaps in vtable

Article: Q168111
Product(s): Microsoft C Compiler
Version(s): winnt:5.0
Operating System(s): 
Keyword(s): kbtool kbCompiler kbVC500bug kbVS97sp1fix
Last Modified: 04-MAY-2001

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The information in this article applies to:

- The C/C++ Compiler (CL.EXE), used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
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SYMPTOMS
========

An access violation may occur when you #import a type library of a COM object
that was produced by Visual Basic 5.0.

CAUSE
=====

The compiler does not compensate for gaps in the vtable left by Visual Basic for
properties that are Objects. The sample code below demonstrates this problem.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This bug has been corrected in Visual Studio 97
Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see
the following article in the Microsoft Knowledge Base:

Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

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

Steps to Reproduce Behavior
---------------------------

1. Place the following Visual Basic code in a Class Module of an ActiveX DLL
  project: Option Explicit Public Obj As Object Public Val As Long

        Private Sub Class_Initialize()
           Val = 2
        End Sub

2. Make a native dll from the above code. In this example, it is named Test.dll
  and the Class Module is named TestClass.

3. Place the following code in a .cpp file: #import "test.dll" no_namespace

        void func()
        {
           _TestClassPtr p( __uuidof(TestClass) );
           int i = p->Val;  // 0xc0000005 here
        }

When the C++ code is executed, an access violation occurs on the commented line
of code.

Additional query words:

======================================================================
Keywords          : kbtool kbCompiler kbVC500bug kbVS97sp1fix 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : winnt:5.0
Issue type        : kbbug
Solution Type     : kbfix

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