FIX: #import Does Not Compensate for Gaps in vtable

• The C/C++ Compiler (CL.EXE), used with:
  • Microsoft Visual C++, 32-bit Editions, version 5.0

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
         } 

Additional query words:

Keywords : kbtool kbCompiler kbVC500bug kbVS97sp1fix
Version : winnt:5.0
Platform : winnt
Issue type : kbbug