Q189735: BUG: Removing Collection Elements Takes Longer Than Expected

Article: Q189735
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, version 6.0 
- Microsoft Visual Basic Professional Edition for Windows, version 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

In Visual Basic 6.0, removing elements from the end of a collection takes longer
than removing elements from the beginning.

CAUSE
=====

When removing an element from a collection, Visual Basic 6.0 begins at the
beginning of the collection and traverses the collection until the desired
element is reached, then that element is removed.

RESOLUTION
==========

Remove elements from the beginning of the collection rather than the end.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. We are researching this bug and will post new
information here in the Microsoft Knowledge Base as it becomes available.

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

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

1. Create a new Standard EXE project in Visual Basic. Form1 is created by
  default.

2. Select Add Module from the Project menu. This will create Module1.

3. Select Project1 Properties from the Project menu. Change the Startup Object
  to Sub Main.

4. Copy and paste the following code into Module1:

        Sub Main()

           Dim c As New Collection
           Dim a As Long

           Set c = New Collection

           'Add elements to collection
           For a = 1 To 10000
              c.Add "Thank you sir, may I have another."
           Next a
           MsgBox "Done adding elements"

           'Remove elements from end, this takes long time
           For a = 10000 To 1 Step -1
              c.Remove a
           Next a
           MsgBox "Done removing elements from end"

           'Add elements to collection again
           For a = 1 To 10000
              c.Add "Thank you sir, may I have another."
           Next a
           MsgBox "Done adding elements"

           'Remove elements from beginning, this is much quicker
           For a = 1 To 10000
              c.Remove 1
           Next a
           MsgBox "Done removing elements from end"
         End Sub

5. Press the F5 key to run the project. Note the time difference between the two
  methods of deleting elements from a collection.

Additional query words: kbDSupport kbVBp600bug kbVBp kbdss kbNoKeyWord

======================================================================
Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVBA600 kbVB600
Issue type        : kbbug

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.