FIX: Access Violation in MSVBVM50 When Passing a Variant Array

View products that this article applies to.

This article was previously published under Q193367

SYMPTOMS

When calling a function of an object in an out-of-process server and passing a Variant array by reference, you get an access violation as below:

The instruction at '0x0f0fdbda' referenced memory at '0x0000b1a4'. The
memory could not be 'read'.

NOTE: The actual memory address may vary. This error occurs after you apply the Service Pack 3 for Visual Basic 5.0

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RESOLUTION

Refer to "Ways to Resolve the Problem" in the MORE INFORMATION section below.

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STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Microsoft Visual Basic, version 6.0.

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MORE INFORMATION

Steps to Reproduce Behavior

The following steps require MDAC 2.0 to be installed on the machine:

Download and install MDAC 2.0. You only need the minimum setup files.
Alternatively, you can replace the existing oleaut32.dll with the version shipped with MDAC 2.0 or Visual Basic 6.0 (2.30.4261).

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Create the Server

Create an ActiveX exe project and rename it ArraySvr.

Add the following code to the default class module (Class1):

      Public Function UseArray(ByRef vArray As Variant) As Boolean
         UseArray = True
      End Function

      Public Function GetArray() As Variant
         Dim vReturn As Variant
         Dim vBstr As Variant
         ReDim vReturn(1, 0) As Variant
         vBstr = "Zero,Zero"
         vReturn(0, 0) = vBstr
         vBstr = "One,Zero"
         vReturn(1, 0) = vBstr
         GetArray = vReturn
      End Function

Compile the server.

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Create and Test Client

Create a Standard EXE project in Visual Basic. Form1 is created by default.
Add two CommandButtons and one Label to Form1.
Select References from the Project menu and add a reference to ArraySvr.

Add the following code to Form1:

      Private vModule As Variant

      Private Sub Command1_Click()
         Dim o As ArraySvr.Class1
         Set o = CreateObject("arraysvr.class1")
         vModule = o.GetArray
         Set o = Nothing
         Command2.Enabled = True
      End Sub

      Private Sub Command2_Click()
         Dim o As ArraySvr.Class1
         Dim vLocal(1, 0) As Variant
         Dim i As Long
         Dim bRet As Boolean
         For i = LBound(vModule, 1) To UBound(vModule, 1)
            vLocal(i, 0) = vModule(i, 0)
            Label1.Caption = vLocal(i, 0)
            Set o = CreateObject("arraysvr.class1")
            bRet = o.UseArray(vLocal)
         Next i
         Set o = Nothing
      End Sub

      Private Sub Form_Load()
         Command2.Enabled = False
      End Sub

Press the F5 key to run the client.
When you press Command1 and then Command2, you should see Label1 display "One,Zero."
Compile the project into Native code.
Run the compiled exe. When you press Command1 and then Command2, you get a message as shown below:
The instruction at '0x0f0fdbda' referenced memory at '0x0000b1a4'.
The memory could not be 'read'.

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Ways to Solve Problem

There are two ways to resolve this problem. You can either compile in P- code or use a temporary Variant variable for the argument as shown in the modified code below:

   Private Sub Command2_Click()
      Dim o As ArraySvr.Class1
      Dim vLocal(1, 0) As Variant
      Dim i As Long
      Dim bRet As Boolean
      Dim vTmp as Variant    'temporary variable for passing argument

      For i = LBound(vModule, 1) To UBound(vModule, 1)
         vLocal(i, 0) = vModule(i, 0)
         Label1.Caption = vLocal(i, 0)
         vTmp = vLocal
         Set o = CreateObject("arraysvr.class1")
         'instead of passing vLocal directly, we pass vTmp
         bRet = o.UseArray(vTmp)
      Next i
      Set o = Nothing
   End Sub

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