How do I make a VB6 variant array with UBound < LBound?

Question

I'm trying to get rid of dependencies on SCRRUN.DLL in a VB6 application. One of the things it's currently being used for is its Dictionary class. The Dictionary class has a Keys function that is supposed to return an array of the keys in the dictionary. I did a little experimentation to see what happens if there are no keys in the dictionary:

Dim D As Dictionary
Set D = New Dictionary
Dim K() As Variant
K = D.Keys
MsgBox LBound(K) & ", " & UBound(K)

I was expecting "subscript out of range", or something similar, but instead I was informed that the LBound is 0 and the UBound is -1.

So, how can I create a Variant array that has LBound 0 and UBound -1?

I've tried just using an uninitialized variant array:

Dim K() as Variant
MsgBox LBound(K) & ", " & UBound(K)

But of course that throws "Subscript out of range", as I would expect. So does erasing an uninitialized array:

Dim K() as Variant
Erase K
MsgBox LBound(K) & ", " & UBound(K)

As does erasing an initialized array:

Dim K() As Variant
ReDim K(0 To 0)
Erase K
MsgBox LBound(K) & ", " & UBound(K)

I also tried just redimming to 0 and -1, strange as that may seem:

Dim K() As Variant
ReDim K(0 To -1)
MsgBox LBound(K) & ", " & UBound(K)

But that also gives "subscript out of range".

Poking around on the web a bit, I found the following trick:

Dim K() As String
K = Split(vbNullString)
MsgBox LBound(K) & ", " & UBound(K)

And that actually does give an array with LBound 0 and UBound -1! Unforunately, it's a String array, whereas I need a Variant array. I can't very well individually copy the Strings from one array to Variants in another array, because, well, 0 to -1 and all.

Does anyone know how to make such an array, Variant() with LBound 0 and UBound -1, without using SCRRUN.DLL? Preferably also using only built-in VB6 stuff, but if you can do it if you're allowed to use some external thing (other than SCRRUN.DLL), I'm all ears. Thanks.

Mccalla

As you noticed in your experiments, you can sometimes run into an unitialized array which will give you the "Subscript out of range" errors -- this is different than an initialized, but empty, array. You may also find this answer to be helpful: https://mcmap.net/q/244843/-how-do-i-determine-if-an-array-is-initialized-in-vb6 – Guillemot

+1 for good research shown in your question – Guillemot

Answer 1

You can use the Array function:

Dim K()
K = Array()
MsgBox UBound(K)

Guillemot

Answer 2

OK, answering my own question (but using OLEAUT32.DLL; I'd still be interested in any solutions that are pure built-in VB6):

Private Declare Function SafeArrayCreateVector Lib "OLEAUT32.DLL" ( _
    ByVal vt As VbVarType, ByVal lLbound As Long, ByVal cElements As Long) _
    As Variant()

Private Const VT_VARIANT As Long = 12

(...)

Dim K() As Variant
K = SafeArrayCreateVector(VT_VARIANT, 0, 0)
MsgBox LBound(K) & ", " & UBound(K)

Mccalla

Here is an in-depth discussion how to construct empty arrays of various types: vbforums.com/… – Earleenearlene