FIX: UserControl in VB4 or VC++ 5.0 Container Causes IPF on Exit (184332)



The information in this article applies to:

  • Microsoft Visual Basic Learning Edition for Windows 5.0
  • Microsoft Visual Basic Professional Edition for Windows 5.0
  • Microsoft Visual Basic Enterprise Edition for Windows 5.0
  • Microsoft Visual Basic Standard Edition, 32-bit, for Windows 4.0
  • Microsoft Visual Basic Professional Edition, 32-bit, for Windows 4.0
  • Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows 4.0
  • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
  • Microsoft Visual C++, 32-bit Professional Edition 5.0

This article was previously published under Q184332

SYMPTOMS

An application compiled in Visual Basic 4.0 or Visual C++ 5.0 generates an "Invalid Page Fault in MSVBVM50.DLL" error when the application is closed.

CAUSE

This error can occur in the following situation:

  • The Visual Basic 4.0 or Visual C++ 5.0 application contains a UserControl created in Visual Basic 5.0.

    -and-

  • The UserControl contains a Class that creates a reference to the UserControl.

    -and-

  • You are running Windows 95 or Windows 98.

RESOLUTION

To work around this problem, use the ObjPtr function in combination with the CopyMemory API call to create the UserControl reference in the Class Module. The steps to complete the workaround are listed in the MORE INFORMATION section of this article.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.
This problem was corrected in Windows 2000.

MORE INFORMATION

WARNING: One or more of the following functions are discussed in this article; VarPtr, VarPtrArray, VarPtrStringArray, StrPtr, ObjPtr. These functions are not supported by Microsoft Technical Support. They are not documented in the Visual Basic documentation and are provided in this Knowledge Base article "as is." Microsoft does not guarantee that they will be available in future releases of Visual Basic.

Steps to Reproduce Behavior
  1. Start a new ActiveX Control project in Visual Basic 5.0.
  2. Name the project "passcontrol."
  3. Add a Class Module to the project.
  4. Add the following code to Class1:
          Private mycontrol As passcontrol.UserControl1
    
          Friend Sub passSelf(obj As passcontrol.UserControl1)
            Set mycontrol = obj
            mycontrol.SayHello
    
          End Sub
    
          Private Sub Class_Terminate()
            Set mycontrol = Nothing
          End Sub
    					
  5. Add the following code to UserControl1:
          Private myclass As New passcontrol.Class1
    
          Private Sub UserControl_Initialize()
            myclass.passSelf Me
          End Sub
    
          Friend Sub SayHello()
            MsgBox "Hello!"
          End Sub
    					
  6. On the File menu, click "Make Passcontrol.ocx" to build the control.
  7. Create a new project in Visual Basic 4.0 (32-bit) or Visual C++ 5.0.
  8. Add Passcontrol.ocx to your project's form.
  9. Compile (or build) the Visual Basic or Visual C++ application.
  10. Run the application on a computer running Windows 95, Windows 98, or Windows Me.
  11. Exit the application. You should receive the error "<application> caused an Invalid Page Fault in Module MSVBVM50.DLL."
WARNING: If you reproduce this problem, it is advisable to restart the computer you are testing on after you receive the error. Passcontrol.ocx is locked by the system, and any attempt to manipulate this file causes your computer to freeze.

Workaround

In the Class Module, substitute the following code:
   Private Declare Sub CopyMemory _
         Lib "kernel32" Alias "RtlMoveMemory" _
            (pDest As Any, _
            pSrc As Any, _
            ByVal ByteLen As Long)

   Private mycontrol As passcontrol.UserControl1
   Friend Sub passSelf(ByVal ptrobj As Long)
      CopyMemory mycontrol, ptrobj, 4
      mycontrol.SayHello
   End Sub

   Private Sub Class_Terminate()
      Set mycontrol = Nothing
   End Sub
				
In the UserControl, substitute the following code:

   Private myclass As New passcontrol.Class1
   Private Sub UserControl_Initialize()
      myclass.passSelf ObjPtr(Me)
   End Sub

   Friend Sub SayHello()
      MsgBox "Hello!"
   End Sub
				

Modification Type:MinorLast Reviewed:3/21/2005
Keywords:kbBug kbCRT kbCtrlCreate kbfix KB184332