FIX: Error When Closing a Program Through the Control Box

• Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 32-bit only, for Windows, version 4.0

SYMPTOMS

An application error occurs when you close a Visual Basic program through the control box if the Visual Basic program executes a command after an object created from a class module is set to nothing. This problem occurs only in the 32-bit edition of Visual Basic 4.0.

RESOLUTION

The workaround to this issue is execute all the code in the event before setting the object to nothing. The statement to set the object to nothing should be the last line in the event procedure.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in Visual Basic 5.0.

MORE INFORMATION

Steps to Reproduce Issue

1. Start the 32-bit version of Visual Basic 4.0 or if it is already running, click New Project on the File menu.



2. Use the following steps to create a class module.
   
   
   • Click Class Module on the Insert Menu. The code window for the class module appears.
   
   
   
   • In the Properties window of the Class1 class module, set the Instancing Property to 2-Createable MultiUse, and the Public property to True.
   
   
   
   • Add the following code to the Class1 code window:

     
           Option Explicit
           Public Name As String
     
           Private Sub Class_Terminate()
              Form1.Print Name
           End Sub
         

   
   
   



3. Add the following code to the Form1 code window.

   
         Option Explicit
         Public A As New Class1
   
         Private Sub Form_Load()
            Show
            Set A = New Class1
            A.Name = "A"
   
            'To workaround this bug, cut the next line
            Set A = Nothing
   
            Print "A Is " & IIf(A Is Nothing, "Nothing", "Something")
            'And uncomment this next line.
            'Set A = Nothing
         End Sub
    




4. Press the F5 key or click Start on the Run menu to run the program.



5. Click Close from the Control Bar menu on the form. One of the following application error displays and Visual Basic ends:

Windows NT 32-bit:

An application error has occurred and an application error log is being generated, VB32.exe Exception: access violation (0xc0000005), Address: 0x001d02d7.

-or-

VB32.EXE-Application Error dialog box. The instruction at "0x001aaff8" referenced memory at "0x007dbd6b". The memory could not be "written".


Windows 95 or Windows 98 32-bit:

VB32 caused an invalid page fault in module <unknown> at 0000:a0000001.

Additional query words: kbVBp400bug kbCrtl kbds kbVBp kbDSupport kbdsd

Keywords : kbGrpVB
Version : 4.00
Platform : NT WINDOWS
Issue type : kbbug