Knowledge Base

FIX: #import Does Not Compensate for Gaps in vtable

Article ID: 168111

Article Last Modified on 7/5/2005

APPLIES TO

Microsoft Visual C++ 5.0 Enterprise Edition
Microsoft Visual C++ 5.0 Professional Edition

This article was previously published under Q168111

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:

170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

Steps to Reproduce Behavior

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

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.

Keywords: kbbug kbfix kbvs97sp1fix kbcompiler KB168111

Microsoft KB Archive/168111

Contents