How to check whether a variant array is unallocated? - vba

Question

Dim Result() As Variant
In my watch window, this appears as
Expression | Value | Type
Result | | Variant/Variant()
How do I check the following:
if Result is nothing then
or
if Result is Not Set then
This is basically what I am trying to accomplish, but the first one does not work and the second does not exist.

Answer 1

To avoid error handling, I used this, seen on a forum long time ago and used sucessfully since then:
If (Not Not Result) <> 0 Then 'Means it is allocated
or alternatively
If (Not Not Result) = 0 Then 'Means it is not allocated
I used this mainly to extend array size from unset array this way
'Declare array
Dim arrIndex() As Variant
'Extend array
If (Not Not Result) = 0 Then
ReDim Preserve Result(0 To 0)
Else
ReDim Preserve Result(0 To UBound(Result) + 1)
End If

Answer 2

Chip Pearson made a useful module called modArraySupport that contains a bunch of functions to test for things like this. In your case, you would want to use IsArrayAllocated.
Public Function IsArrayAllocated(Arr As Variant) As Boolean
This function returns TRUE or FALSE indicating whether the specified array is allocated (not empty). Returns TRUE of the
array is a static array or a dynamic that has been allocated with a Redim statement. Returns FALSE if the array is a dynamic array that
has not yet been sized with ReDim or that has been deallocated with the Erase statement. This function is basically the opposite of
ArrayIsEmpty. For example,
Dim V() As Variant
Dim R As Boolean
R = IsArrayAllocated(V) ' returns false
ReDim V(1 To 10)
R = IsArrayAllocated(V) ' returns true
The technique used is basically to test the array bounds (as suggested by #Tim Williams) BUT with an extra gotcha.
To test in your immediate window:
?IsArrayAllocated(Result)
Testing in Watch window: there are may ways to do this; for example, add a watch on R and under "Watch Type" select "Break When Value Changes".

Answer 3

You can use the following in the immediate window:
?Result Is Nothing
?IsNull( Result )
?IsEmpty( Result )
?IsMissing( Result )
The first is simply for completeness. Since Result is not an object, Result Is Nothing will throw an error. Empty is for variants that have not been initialized including arrays which have not been dimensioned..
(Update) In doing some additional checking, I have discovered that IsEmpty will never return true on a declared array (whether Redim'd or not) with only one exception. The only exception I found is when the array is declared at the module level and not as Public and then only when you check it in the immediate window.
Missing if for optional values passed to a function or sub. While you cannot declare Optional Foo() As Variant, you could have something like ParamArray Foo() As Variant in which case if nothing is passed, IsMissing would return true.
Thus, the only way to determine if the array is initialized is to write a procedure that would check:
Public Function IsDimensioned(vValue As Variant) As Boolean
On Error Resume Next
If Not IsArray(vValue) Then Exit Function
Dim i As Integer
i = UBound(Bar)
IsDimensioned = Err.Number = 0
End Function
Btw, it should be noted that this routine (or the library posted by Jean-François Corbett) will return false if the array is dimensioned and then erased.

Answer 4

I recommend a slightly different approach because I think using language artifacts like (Not Array) = -1 to check for initialization is difficult to read and causes maintenance headaches.
If you are needing to check for array allocation, most likely it's because you're trying to make your own "vector" type: an array that grows during runtime to accommodate data as it is being added. VBA makes it fairly easy to implement a vector type, if you take advantage of the type system.
Type Vector
VectorData() As Variant
VectorCount As Long
End Type
Dim MyData As Vector
Sub AddData(NewData As Variant)
With MyData
' If .VectorData hasn't been allocated yet, allocate it with an
' initial size of 16 elements.
If .VectorCount = 0 Then ReDim .VectorData(1 To 16)
.VectorCount = .VectorCount + 1
' If there is not enough storage for the new element, double the
' storage of the vector.
If .VectorCount > UBound(.VectorData) Then
ReDim Preserve .VectorData(1 To UBound(.VectorData) * 2)
End If
.VectorData(.VectorCount) = NewData
End With
End Sub
' Example of looping through the vector:
For I = 1 To MyData.VectorCount
' Process MyData.VectorData(I)
Next
Notice how there's no need to check for array allocation in this code, because we can just check the VectorCount variable. If it's 0, we know that nothing has been added to the vector yet and therefore the array is unallocated.
Not only is this code simple and straightforward, vectors also have all the performance advantages of an array, and the amortized cost for adding elements is actually O(1), which is very efficient. The only tradeoff is that, due to how the storage is doubled every time the vector runs out of space, in the worst case 50% of the vector's storage is wasted.

Answer 5

Check the LBound of the array. If you get an error then it's uninitialized.