[RESOLVED] Dynamic array: has it been initialized?

[krtxmrtz]

I'm not sure I've chosen a proper title for this thread, anyway, I want to test if a dynamic array has already been ReDim-ed. In other words, what should I replace '???' by?

Dim MyArray() As Integer
ReDim MyArray(10)

If ??? Then
    'Do this
Else
    'Do that
End If

??? means that the bold statement has been executed.

[vbfbryce]

I'm sure there's a better way, but try this:

    Dim MyArray() As Integer
    ReDim MyArray(10)

    On Error Resume Next
    MsgBox UBound(MyArray)
    If Err.Number <> 0 Then
        MsgBox Err.Description
    End If

Then comment out the "ReDim" and run it again.

[krtxmrtz]

I'm sure there's a better way, but try this:

    Dim MyArray() As Integer
    ReDim MyArray(10)

    On Error Resume Next
    MsgBox UBound(MyArray)
    If Err.Number <> 0 Then
        MsgBox Err.Description
    End If

Then comment out the "ReDim" and run it again.

Trapping the error, yes, there's always that, but I was thinking of something more elegant, you know, IsNull, IsNothing, IsEmpty, IsWhatNot or similar.

[MartinLiss]

There's nothing (no pun intended) built in.

[MartinLiss]

If 0 isn't valid in MyArray(0) then you can do this

If MyArray(LBound(MyArray)) = 0 Then
    MsgBox "empty"
End If

[Teseng]

I've used this, I've never ran into a problem with it. The Assert is there to prevent some buggy things from happening.

Function CheckArray(MyInt() As Integer) As Boolean
Dim i As Long
i = Not Not MyInt
Debug.Assert App.hInstance
If Not i = 0 Then
CheckArray = True
Else
CheckArray = False
End If
End Function

Usage:

Sub TestSub()
Dim MyInt1() As Integer, MyInt2() As Integer
ReDim MyInt2(3 To 5)
MsgBox CheckArray(MyInt1) 'Return False, the Array IS NOT initialized
MsgBox CheckArray(MyInt2) ' Return True, the array IS initialized
End Sub

[Edgemeal]

Would this help?

Dim MyArray() As Integer
' ReDim MyArray(10)

' Check if Array is empty
If (Not MyArray()) = -1 Then
    MsgBox "Array Empty/Not Dimensioned"
Else
    'Do that
End If

[krtxmrtz]

If 0 isn't valid in MyArray(0) then you can do this

If MyArray(LBound(MyArray)) = 0 Then
    MsgBox "empty"
End If

Gives "subscript out of range" because MyArray hasn't been initialized yet.

[krtxmrtz]

I've used this, I've never ran into a problem with it. The Assert is there to prevent some buggy things from happening.

Function CheckArray(MyInt() As Integer) As Boolean
Dim i As Long
i = Not Not MyInt
Debug.Assert App.hInstance
If Not i = 0 Then
CheckArray = True
Else
CheckArray = False
End If
End Function

Usage:

Sub TestSub()
Dim MyInt1() As Integer, MyInt2() As Integer
ReDim MyInt2(3 To 5)
MsgBox CheckArray(MyInt1) 'Return False, the Array IS NOT initialized
MsgBox CheckArray(MyInt2) ' Return True, the array IS initialized
End Sub

Well, it works, but what buggy things do you mean?

[krtxmrtz]

Would this help?

Dim MyArray() As Integer
' ReDim MyArray(10)

' Check if Array is empty
If (Not MyArray()) = -1 Then
    MsgBox "Array Empty/Not Dimensioned"
Else
    'Do that
End If

Yes it does!

[Code Doc]

Seems to me that you would have to check all the integer elements of the array. Only if all were 0 would it then be safe to ReDim it unless you purposely want to reset all of the elements to 0.

[RhinoBull]

If you don't like the error trapping way (simplest and bulletproof) then try this:

Determining Array Initialization State and Dimensions

[krtxmrtz]

Seems to me that you would have to check all the integer elements of the array. Only if all were 0 would it then be safe to ReDim it unless you purposely want to reset all of the elements to 0.

Well, I'm not sure I follow you. The idea is, some code must be skipped if the array hasn't been yet redim-ed and given values.

[anhn]

A strange use of "Not Not" that Tseng mentioned in post#6

    Dim MyArray() As Integer
    
    If (Not Not MyArray) = 0 Then
        MsgBox "MyArray was Not Initialized"
    Else
        MsgBox "MyArray was Initialized with UBound = " & UBound(MyArray)
    End If
    
    ReDim MyArray(10)
    
    If (Not Not MyArray) = 0 Then
        MsgBox "MyArray was Not Initialized"
    Else
        MsgBox "MyArray was Initialized with UBound = " & UBound(MyArray)
    End If

[krtxmrtz]

If you don't like the error trapping way (simplest and bulletproof) then try this:

Determining Array Initialization State and Dimensions

Thank you, I bookmark the site for possible future reference. However I like edgemels's solution in just one statement.

Trapping the error is a matter of taste, offhand I sort of dislike it as it looks like you're mending some faulty code, but I imagine it's just a matter of getting used to it.

[RhinoBull]

Trapping the error is a matter of taste, offhand I sort of dislike it as it looks like you're mending some faulty code, but I imagine it's just a matter of getting used to it.

Nope, not in this case at least.

[krtxmrtz]

A strange use of "Not Not" that Tseng mentioned in post#6...

I assume

If (Not MyArray()) = -1 Then

is the same as

If (Not Not MyArray) = 0 Then

[krtxmrtz]

Nope, not in this case at least.

Well, perhaps you've convinced me that error trapping is ok, still it takes one more statement (On Error Resume Next)

[DrUnicode]

Have your tried API SafeArrayGetDim?

Private Declare Function SafeArrayGetDim Lib "oleaut32.dll" (ByRef saArray() As Any) As Long

Private Type ProjectType
    ProjectCode As String
    Priority As Integer
End Type

Private Sub Form_Load()
   Dim l() As Long
   Debug.Print "IsArrayInitiaized l()", SafeArrayGetDim(l) > 0
   ReDim l(0)
   Debug.Print "IsArrayInitiaized l(0)", SafeArrayGetDim(l) > 0
   Debug.Print
   '
   Dim s() As String
   Debug.Print "IsArrayInitiaized s()", SafeArrayGetDim(s) > 0
   ReDim s(0)
   Debug.Print "IsArrayInitiaized s(0)", SafeArrayGetDim(s) > 0
   Debug.Print
   '
   Dim v() As Variant
   Debug.Print "IsArrayInitiaized v()", SafeArrayGetDim(v) > 0
   ReDim v(0)
   Debug.Print "IsArrayInitiaized v(0)", SafeArrayGetDim(v) > 0
   Debug.Print
   
   Dim p() As ProjectType
   Debug.Print "IsArrayInitiaized p()", SafeArrayGetDim(p) > 0
   ReDim p(0) As ProjectType
   Debug.Print "IsArrayInitiaized p(0)", SafeArrayGetDim(p) > 0
End Sub

[Teseng]

Well, it works, but what buggy things do you mean?

For some reason, the Not Not Method, does something to the array pointer, and unless you do the assert, it can cause some wacky things, such as "i = 1 + 1" will give the error "math too complex" The assert fixes it completely, i don't understand it completely, but it seems to work fine.

[krtxmrtz]

Have your tried API SafeArrayGetDim?
...

I like it,

I have used much the API function compilation at allapi
but it's no longer maintained and up to date so, this function I didn't know about.

[Milk]

Not Not Arrayname

This returns the address of the Safearray Descriptor used by VB to describe arrays. If an Array is uninitialised this pointer is null hence If Not Arrayname <> -1 Then initialised

I don't think this feature is there by design and there is a bug. The bug only happens in the IDE and only in the first floating point calculation following the first use of Not Arrayname. The bug can be avoided by calling any internal class after the first use of Not Arrayname

Debug.Assert App.hInstance '<-- this avoids the IDE only bug and does not compile

[vb5prgrmr]

For an in depth dicussion on this subject just a little over a year ago on another site, see...

http://www.tek-tips.com/viewthread.cfm?qid=1495917

Hope it helps...




Good Luck

[CDRIVE]

I found this thread while researching the same issue as krtxmrtz. Though this thread is resolved, I just wanted to say that all contributors made this a stimulating read.

[xiaoyao]

True,UsedTime2=0.0349 Ms--GetLbound
True,UsedTime1=0.0494 Ms--API--CopyMemory--IsArrayReDims
True,UsedTime2=0.0099 Ms--API--SafeArrayGetDim

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Dest As Any, Src As Any, ByVal cb&)
Private Declare Function SafeArrayGetDim Lib "oleaut32.dll" (ByRef saArray() As Any) As Long

Function GetLbound(array1 As Variant) As Boolean
    On Error Resume Next
    Dim a As Long
    a = LBound(array1)
    GetLbound = Err.Number = 0
End Function

Public Function IsArrayReDims(wArray As Variant) As Boolean
'?????????
    Dim a As Long
    If IsArray(wArray) Then
        CopyMemory a, ByVal VarPtr(wArray) + 8, 4
        CopyMemory a, ByVal a, 4
    End If
IsArrayReDims = a <> 0
End Function

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)
    timeEndPeriod 1
End Sub
Function CheckArray(MyArray As Variant) As Boolean
If (Not MyArray()) = -1 Then
Else
    CheckArray = True
End If
End Function