[RESOLVED] VB6 - Unsigned data type (Can I trick?)

[Dave Sell]

OK I'm not very hopeful of a resolution but I thought I'd give it a shot here.

I have an OPC Simulator that I can create "in-memory arrays". These arrays can be of various data types. For example they can be VT_I2, VT_I4, VT_UI2, etc...

If these look familiar to you then keep reading... AFAIK I2 = Signed Integer, I4 = Singed Long (both native VB6 data types). Ergo, UI2 = Unsigned Integer, however VB6 cannot declare a variable as an Unsigned Int or Long (a known limitation to VB6).

As you may have guessed, I have successfully Read data from and Written data to the VT_I2 and the VT_I4 arrays, but am unable to Write to the VT_UI2 array (although strangely I can read from it).

I will try to condense all the code as small as possible.

Public Enum CanonicalDataTypes
    CanonDtShort = 2 ' VT_I2
    CanonDtLong = 3 ' VT_I4
    CanonDtFloat = 4
    CanonDtDouble = 5
    CanonDtString = 8
    CanonDtBool = 11
    CanonDtChar = 16
    CanonDtByte = 17
    CanonDtWord = 18 ' VT_UI2
    CanonDtDword = 19 ' VT_UI4
    CanonDtArray = 8192 ' VT_Array
End Enum

The following code works for Longs (VT_I4):

Sub AddOPCItem
    '
    Dim Types(1) As Integer
    '
    ' Works:
    '
    ' VT_I4
    OPCItemIDs(1) = "Device_1.aLong"
    Types(1) = CanonDtLong + CanonDtArray
    '
    ' ...
    '
    Dim RequestedDataType As Variant
    RequestedDataType = CVar(Types)
    '
    OPCItemCollection.AddItems ItemCount, OPCItemIDs, ClientHandles, ItemServerHandles, ItemServerErrors, RequestedDataType
    '
End Sub
 
Sub WriteOPC
    '
    Dim Vals(4) As Long ' DHS good for LONGs (VT_I4)
    '
    For i = 1 To 4
        Vals(i) = CLng("SomeNumericValue")
    Next
    '
    ' ...
    '
    ASyncItemValues(1) = CVar(Vals)
    ConnectedGroup.AsyncWrite ItemCount, ASyncItemServerHandles, ASyncItemValues, ASyncItemServerErrors, TransactionID, CancelID
    '
End Sub

The following code works for Integers (VT_I2):

Sub AddOPCItem
    '
    Dim Types(1) As Integer
    '
    ' Works:
    '
     VT_I2
    OPCItemIDs(1) = "Device_1.aShort"
    Types(1) = CanonDtShort + CanonDtArray
    '
    ' ...
    '
    Dim RequestedDataType As Variant
    RequestedDataType = CVar(Types)
    '
    OPCItemCollection.AddItems ItemCount, OPCItemIDs, ClientHandles, ItemServerHandles, ItemServerErrors, RequestedDataType
    '
End Sub
 
Sub WriteOPC
    '
    Dim Vals(4) As Integer ' DHS - good for SHORTs (VT_I2)
    '
    For i = 1 To 4
        Vals(i) = CInt("SomeNumericValue")
    Next
    '
    ' ...
    '
    ASyncItemValues(1) = CVar(Vals)
    ConnectedGroup.AsyncWrite ItemCount, ASyncItemServerHandles, ASyncItemValues, ASyncItemServerErrors, TransactionID, CancelID
    '
End Sub

As you can see I can define a VB array of Integers to Write data down to VT_I2's and I can define a VB array of Longs to Write data down to VT_I4's.

However I am unable to create a VB array such that I can Write down to VT_UI2's or VT_UI4's.

I have tried using VB arrays of Integers and VB arrays of Longs in an attempt to Write data down to the VT_UI2 and VT_UI4 OPC arrays, but no data gets written down. No error is reported on either end. Its just like nothing happens.

Question: Can I create a VB Array of "Somethings" to trick the transport layer into accepting something as an Unsigned data type?

I have seen some blurbs about SAFEARRAYs but am unsure how that fits into the equation...

Thanks!

Dave