PRB: Memory Corruption in VB4-16 When Passing Recordset to Sub

• Microsoft Visual Basic Professional Edition, 16-bit only, for Windows, version 4.0

SYMPTOMS

When passing a recordset to another Sub or Function, you see memory corruption or may experience a general protection fault (GP fault) in Vba5.dll.

CAUSE

The called procedure may be declaring the recordset "As Object" instead of "As Recordset".

RESOLUTION

Change the declaration in the called procedure to "As Recordset".

STATUS

Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Microsoft provides code examples for illustration only, without warranty either expressed or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.

This code is provided 'as is' and Microsoft does not guarantee that the following code can be used in all situations. Microsoft does not support modifications of the code to suit customer requirements for a particular purpose.

Steps to Reproduce Behavior

1. In Microsoft Access 2.0 or another front-end, create a Jet 2.x database (or use NWIND or BIBLIO) and add the following table:

         Table: Table1
           Field: K1    Long
           Field: K2    Long
           Field: K3    Text (3)
           Field: Desc Text
   
   

2. Make a composite primary key, consisting of K1, K2, and K3, and then save the table design.

3. Add the following data:

         K1   K2   K3   Desc
         1234   22222   abc   xxxxxxxxxxx
         1234   22222   def   xxxxxxxxxxx
         1234   22222   ghi   xxxxxxxxxxx
         1234   22222   jkl   xxxxxxxxxxx
   
   

4. Create a Visual Basic 4.0 16-bit application.

5. Add a command button (Command1) to the form.

6. Add the following code to the form:

         option Explicit
   

         Private Sub Command1_Click()
         Dim db As Database, rs As Recordset
           Set db = DBEngine(0).OpenDatabase _
                 ("c:\office\access20\sampapps\nwind.mdb") ' alter as needed
           Set rs = db.OpenRecordset("Table1")
           rs.Index = "PrimaryKey"
           Test_Call rs
           rs.Close
           db.Close
         End Sub
   
         Sub Test_Call(rs As Object)
         Dim K1 As Long, K2 As Long, K3(3) As String, I As Long
           K1 = 1234
           K2 = 22222
           K3(0) = "abc"
           K3(1) = "def"
           K3(2) = "ghi"
           K3(3) = "jkl"
           Debug.Print "Pass 1"
           For I = 0 To 3
             rs.Seek "=", K1, K2, K3(I)
             Debug.Print I; K1; K2; K3(0), K3(1), K3(2), K3(3)
           Next I
           Debug.Print "Pass 2"
           For I = 0 To 3
             rs.Seek "=", K1, K2, K3(I)
             Debug.Print I; K1; K2; K3(0), K3(1), K3(2), K3(3)
           Next I
           Debug.Print "Pass 3"
           For I = 0 To 3
             rs.Seek "=", K1, K2, K3(I)
             Debug.Print I; K1; K2; K3(0), K3(1), K3(2), K3(3)
           Next I
         End Sub
   
   

7. Make sure you change the .OpenDatabase method to correctly point to the database.

8. Run the application and click the command button. You may need to do this several times to see the error.

Result

You should see either intermittent and worsening corruption of variables in the Debug Window, or you may get a GP fault in Vba5.dll.

Workaround

Change "Sub Test_Call (rs As Object)" to "Sub Test_Call(rs As Recordset)".

NOTE: This problem does not appear in Visual Basic 4.0 32-bit.