How to create an empty array of Double

Question

I trying to create an empty/defined array of Double which would reflect as Double(0, -1).

I'm able to create one for an array of String, Variant and Byte:

  Dim arr_variant() As Variant
  arr_variant = Array()        ' Variant(0 to -1) '

  Dim arr_string() As String
  arr_string = Split(Empty)    ' String(0 to -1) '

  Dim arr_byte() As Byte
  arr_byte = ""                ' Byte(0 to -1) '

  Dim arr_double() As Double
  arr_double = ???             ' Double(0 to -1) '

, but still haven't found a way for Double.

Maybe with LSet or with a native function?

I think the answer below is probably true, but if you really really want to dive into details, I suggest these two pages: bytecomb.com/… and bytecomb.com/vba-scalar-variables-and-pointers-in-depth. — Sam
– Sam, Commented Jul 28, 2017 at 13:07
@Wolfie, are you really asking why I would need to create a zero length typed array? Well an array not defined doesn't work with UBound, LBound and For Each, but mainly because I need an huge array initialized with 0 that I can compute and filter and where the expected output can be zero items. I'm still amazed to see that it's not possible with Redim arr(0, -1) and that the language doesn't offer a simple way to do it. — michael
– michael, Commented Jul 28, 2017 at 20:47
Initialising it with 0 is doable though, and why can't you output 0 items in an untyped array? I was just curious because I can't think of a situation when a quick check for emptiness wouldn't belay any concerns... — Wolfie
– Wolfie, Commented Jul 28, 2017 at 21:34

michael · Accepted Answer · 2017-07-28 18:19:25Z

3

It seems that the only way is to call a native function:

Private Declare PtrSafe Function SafeArrayRedim Lib "OleAut32" ( _
  ByVal arr As LongPtr, ByRef dims As Any) As Long


Public Sub RedimDouble(arr() As Double, ByVal count As Long)
  If count Then
    ReDim Preserve arr(0 To count - 1)
  Else
    ReDim arr(0 To 0)
    SafeArrayRedim Not Not arr, 0@
  End If
End Sub


Public Sub Usage()

  Dim arr_double() As Double
  RedimDouble arr_double, 0    ' Double(0 to -1) '

End Sub

answered Jul 28, 2017 at 18:19

michael

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stenci Over a year ago

Not Not arr returns 0 and the call to SafeArrayRedim does nothing

Vityata · Accepted Answer · 2017-07-28 12:41:25Z

1

I would go with - not possible.

Take a look at the following code:

Option Explicit
Sub TestMe()
    Dim arr                   'Line 1
    arr = Array(CDbl(0))      'Line 2
    arr = Array(Empty)        'Line 3
End Sub

Line 1 - It takes a Variant array

Line 2 - Makes it Double array

Line 3 - When emptied, it is converted from double to Variant again.

answered Jul 28, 2017 at 12:41

Vityata

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1 Comment

michael Over a year ago

That's rather presumptuous to state that it's not possible since it's technically possible with a safe array. If not with a VBA function, there should be a way with a native function like RtlMoveMemory or SafeArrayRedim. And how is your code relevant to the post? The array from your example is a Variant array of and not a Double array.

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