ACC2: GPF Using List Box Fill Function with Requery Method

• Microsoft Access version 2.0

SYMPTOMS

When you fill a list box using an Access Basic function, and the function returns a static variable upon receiving the close code (8), and you then use the Requery method to requery the list box, you receive a general protection (GP) fault.

CAUSE

The temporary string created by the list box fill function is not freed, and conflicts with another variable used internally by Microsoft Access.

RESOLUTION

Use one of the following techniques to work around this problem:

• Use a Requery action instead of the Requery method for requerying the list box.
• Do not return a static string when your function exits through the close code (8). That is, dimension the variable to make it dynamic, rather than declaring it static.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Access version 2.0. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps to Reproduce Problem

WARNING: Following these steps will result in a GP fault. Save and then close any open work on your computer before following these steps.

NOTE: In the following example, an underscore (_) at the end of a line is used as a line-continuation character. Remove the underscore from the end of the line when re-creating this example.

1. Start Microsoft Access and open the sample database NWIND.MDB.

2. Create a new, blank form.

3. Click the Code button on the toolbar, or choose Code from the View menu, and then enter the following code in the form module:

         Option Compare Database   'Use database order for string _
                                    comparisons.
   
         Dim iTotTables As Integer
         Dim My_CurrDB As Database
         Dim TableList2() As String
         Dim iTotFlds As Integer
         Dim FieldList() As wlib_FldInfo
   
         Function FillTables (fld As Control, handle As Long, lRow As _
         Long, lCol As Long, iMsg As Integer) As Variant
   
            Static returnval As Variant
            ' If you change the above line to the following the error
            ' will not occur:
            ' Dim returnval As Variant
   
            Select Case iMsg
               Case LB_INITIALIZE
                  returnval = -1&
               Case LB_OPEN
                  returnval = Timer
               Case LB_GETROWCOUNT
                  returnval = iTotTables
               Case LB_GETCOLUMNCOUNT
                  returnval = 1
               Case LB_GETCOLUMNWIDTH
                  returnval = -1&
               Case LB_GETVALUE
                  returnval = TableList2(lRow + 1)
               Case LB_GETFORMAT
               Case LB_CLOSE
               Case LB_END
             End Select
             FillTables = returnval
          End Function
   
   

4. Add the following command button and list box to the form:

         Command button:
            Name: Button0
            Caption: Requery Table List
   
         List box:
            Name: Field1
            RowSourceType: FillTables
   
   

5. Set the command button's OnClick property to the following event procedure:

         Sub Button0_Click ()
            Set My_CurrDB = DBEngine.Workspaces(0).Databases(0)
            iTotTables = wlib_GetObjList(My_CurrDB, A_TABLE, TableList2(),_
             False, &HFFFFFFFF)
            Me!Field1.Requery
         End Sub
   
   

6. View the form in Form view.

7. Click the Requery Table List button 8 or more times. You will receive the error message:

         General Protection Fault in MSABC200.DLL at 000B:07E1
   

REFERENCES

For more information about using Access Basic code to fill a list box, search for "filling list boxes/combo boxes" then "Filling a List Box or Combo Box Using an Access Basic Function" using the Microsoft Access Help menu.