Q129933: PRB: Comparing Bookmarks Generates Type Mismatch Error

Article: Q129933
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0
Operating System(s): 
Keyword(s): kbcode
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
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SYMPTOMS
========

If you attempt to use the Bookmark property in a compare operation with another
bookmark, you receive the following error if the bookmarks are not first stored
in string variables:

  Run-time error 13 - Type Mismatch

CAUSE
=====

This is by design. Bookmarks in Visual Basic version 4.0 are stored in byte
arrays. Arrays cannot be directly compared to each other.

RESOLUTION
==========

Before accessing the Bookmark property, copy the bookmark values to string
variables, and make all comparisons using the string variables. The following
code compares two bookmarks correctly.

Step-by-Step Example
--------------------

1. Start a new project in Visual Basic. Form1 is created by default.

2. In the click event for Form1, place the following code:

     Private Sub Form_Click()
        Dim Db As Database
        Dim Rs As Recordset
        Dim Cs As Recordset
        Dim sBook1 as String
        Dim sBook2 as String

        Set Db = DBEngine.Workspaces(0).OpenDatabase("biblio.mdb")
        Set Rs = Db.OpenRecordset("authors", dbOpenDynaset)
        Set Cs = Rs.Clone()

        sBook1 = Rs.Bookmark
        sBook2 = Cs.Bookmark

        If sBook1 = sBook2 Then
           MsgBox "Match"
        Else
           MsgBox "No Match"
        End If
     End Sub

3. Run the program by pressing the F5 key.

STATUS
======

This behavior is by design.

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

Steps to Reproduce Problem
--------------------------

Use the above example, but replace the code in the Form_Click procedure with this
code:

     Private Sub Form_Click()
        Dim Db As Database
        Dim Rs As Recordset
        Dim Cs As Recordset

        Set Db = DBEngine.Workspaces(0).OpenDatabase("biblio.mdb")
        Set Rs = Db.OpenRecordset("authors", dbOpenDynaset)
        Set Cs = Rs.Clone()

        If Rs.Bookmark = Cs.Bookmark Then  'Error 13 - Type Mismatch
           MsgBox "Match"
        else
           MsgBox "No Match"
        End If
     End Sub

Additional query words: 4.00 vb4win vb4all

======================================================================
Keywords          : kbcode 
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch
Version           : WINDOWS:4.0
Issue type        : kbprb

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