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Thread: VB Snippet - Determine if Array is Empty

  1. #1

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    VB Snippet - Determine if Array is Empty

    VB Code:
    1. Private Function isArrayEmpty(arr as Variant) As Boolean
    2.  
    3.  Dim dblCount As Double
    4.  
    5.  isArrayEmpty = True
    6.  
    7.  On Error Resume Next
    8.  
    9. ' CAUSES AN ERROR IF EMPTY
    10.  
    11.  dblCount = Ubound(arr)
    12.  
    13.  If Err.Number > 0 Then Exit Function
    14.  
    15.  isArrayEmpty = False
    16.  
    17. End Function
    Last edited by James Stanich; Feb 20th, 2003 at 11:11 PM.
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  2. #2
    Former Admin/Moderator MartinLiss's Avatar
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    Suggestion - change your Subject to something like "Determine if array is empty" since that's what the code is doing. Your current subject implies that it returns the number of array elements and it doesn't.

  3. #3
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    Re: VB Snippet - Determine if Array is Empty

    I know that this is the old topic, but I think this code will be useful to quickly determine if array is not initialized:
    Fastest method:
    VB Code:
    1. Dim a() As Long
    2. If SAPtr(a) = 0 Then
    3.   MsgBox "Not initialized"
    4. Else
    5.   MsgBox "Initialized"
    6. End If
    SAPtr it is TLB-declared function:
    С Code:
    1. [entry("GetMem4")]
    2.         HRESULT __stdcall SAPtr(
    3.             [in]            SAFEARRAY(void) *   Array,
    4.             [out, retval]   long *              lpRetVal
    5.         );
    You can find the Type Library in the my last topics...

    Not so fast, but very easy method:
    VB Code:
    1. Dim a() As Long
    2. If (Not a) = -1 Then
    3.   MsgBox "Not initialized"
    4. Else
    5.   MsgBox "Initialized"
    6. End If
    and with the same speed:
    VB Code:
    1. Dim a() As Long
    2. If (Not Not a) = 0 Then
    3.   MsgBox "Not initialized"
    4. Else
    5.   MsgBox "Initialized"
    6. End If
    Last edited by Filyus; Jul 11th, 2012 at 10:59 AM.

  4. #4
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    Re: VB Snippet - Determine if Array is Empty

    if (not arr) = -1 then

    seems duplicated

  5. #5
    PowerPoster Elroy's Avatar
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    Re: VB Snippet - Determine if Array is Empty

    Here's what I've used for years:

    Code:
    
    Option Explicit
    '
    Private Declare Function GetMem2 Lib "msvbvm60" (ByRef Source As Any, ByRef Dest As Any) As Long ' Always ignore the returned value, it's useless.
    Private Declare Function GetMem4 Lib "msvbvm60" (ByRef Source As Any, ByRef Dest As Any) As Long ' Always ignore the returned value, it's useless.
    '
    
    Public Function IsPtrDimmed(pArray As Long, Optional FailOnZeroNegOne As Boolean = True) As Boolean
        ' Works with all array types (static or dynamic), including UDTs, but with these exceptions:
        '       Excludes BSTR String arrays.  Use IsStrDimmed instead.
        '       Excludes Varants CONTAINING arrays.
        '    Varant arrays (not an array containing a varant) will work fine.
        '    Also fixed-length String arrays (static or dynamic) work just fine.
        '    Object arrays (early or late bound) will work just fine.
        '
        ' Example:  If IsPtrDimmed(ArrPtr(SomeArray())) Then ...
        '
        Dim pSA As Long
        Dim cDims       As Integer
        Dim cElements   As Long
        '
        If pArray = 0& Then Exit Function                               ' Can happen on String arrays.
        GetMem4 ByVal pArray, pSA                                       ' De-reference.
        If pSA = 0& Then Exit Function                                  ' Dynamic undimensioned array.
        '
        GetMem2 ByVal pSA, cDims
        If cDims = 0 Then Exit Function                                 ' This would be unusual, but just in case.
        '
        GetMem4 ByVal PtrAdd(pSA, 16&), cElements
        If cElements = 0& And FailOnZeroNegOne Then Exit Function       ' Decide what to do about 0 to -1 arrays.
        '
        ' If we fell through to here, we should be looking at an array with elements.
        ' Or, we specified FailOnZeroNegOne=False, and it's one of those.
        IsPtrDimmed = True
    End Function
    
    Public Function PtrAdd(ByVal Ptr As Long, ByVal iOffset As Long) As Long
        ' For adding (or subtracting) a small number from a pointer.
        ' Use PtrAddEx for adding (or subtracting) large numbers from a pointer.
        PtrAdd = (Ptr Xor &H80000000) + iOffset Xor &H80000000
    End Function
    
    
    
    It has the advantage of not invoking error trapping. And, as such, is almost certainly quite a bit faster than an error trapping approach.

    As noted, the only arrays it won't work with are String arrays and Variants containing arrays. Regarding String arrays, I still use error trapping to check those. Regarding Variants containing arrays, basically, I just almost never do that. (It works fine for an array of Variants.)

    Regards,
    Elroy

    EDIT: Also, to use that, you'll need the following declared somewhere:

    Code:
    
    Public Declare Function ArrPtr Lib "msvbvm60" Alias "VarPtr" (a() As Any) As Long
    
    
    Last edited by Elroy; Oct 16th, 2021 at 11:10 AM.
    Any software I post in these forums written by me is provided “AS IS” without warranty of any kind, expressed or implied, and permission is hereby granted, free of charge and without restriction, to any person obtaining a copy. Please understand that I’ve been programming since the mid-1970s and still have some of that code. My contemporary VB6 project is approaching 1,000 modules. In addition, I have a “VB6 random code folder” that is overflowing. I’ve been at this long enough to truly not know with absolute certainty from whence every single line of my code has come, with much of it coming from programmers under my employ who signed intellectual property transfers. I have not deliberately attempted to remove any licenses and/or attributions from any software. If someone finds that I have inadvertently done so, I sincerely apologize, and, upon notice and reasonable proof, will re-attach those licenses and/or attributions. To all, peace and happiness.

  6. #6
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    Re: VB Snippet - Determine if Array is Empty

    Here's another one, making use of a widely known typelib:

    Code:
    Option Explicit
    
    'Reference to:
    '
    '   Visual Basic 6 Virtual Machine Type Library 1.0 by Michel Rutten - Declarations
    '   and aliases for (undocumented) functions in the VB6 runtime library.
    '
    '   {VBVM6Lib.tlb}
    '
    'Docs & download:
    '
    '   http://www.xbeat.net/vbspeed/i_VBVM6Lib.html
    '
    
    Private Sub Main()
        Dim L() As Long
        Dim S() As String
    
        MsgBox "L: " & CStr(MemLong(ArrPtr(L)) = 0) & vbNewLine _
             & "S: " & CStr(MemLong(StrArrPtr(S)) = 0), _
               vbOKOnly, _
               "Emptiness"
        ReDim L(1)
        ReDim S(1, 1)
        MsgBox "L: " & CStr(MemLong(ArrPtr(L)) = 0) & vbNewLine _
             & "S: " & CStr(MemLong(StrArrPtr(S)) = 0), _
               vbOKOnly, _
               "Emptiness"
        MsgBox "L: " & CStr(MemWord(MemLong(ArrPtr(L)))) & vbNewLine _
             & "S: " & CStr(MemWord(MemLong(StrArrPtr(S)))), _
               vbOKOnly, _
               "Number of dimensions"
    End Sub

  7. #7
    PowerPoster Elroy's Avatar
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    Re: VB Snippet - Determine if Array is Empty

    Also, just as an FYI, the OP's code won't fail on a 0 to -1 array, which does occasionally happen.
    Any software I post in these forums written by me is provided “AS IS” without warranty of any kind, expressed or implied, and permission is hereby granted, free of charge and without restriction, to any person obtaining a copy. Please understand that I’ve been programming since the mid-1970s and still have some of that code. My contemporary VB6 project is approaching 1,000 modules. In addition, I have a “VB6 random code folder” that is overflowing. I’ve been at this long enough to truly not know with absolute certainty from whence every single line of my code has come, with much of it coming from programmers under my employ who signed intellectual property transfers. I have not deliberately attempted to remove any licenses and/or attributions from any software. If someone finds that I have inadvertently done so, I sincerely apologize, and, upon notice and reasonable proof, will re-attach those licenses and/or attributions. To all, peace and happiness.

  8. #8
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    Re: VB Snippet - Determine if Array is Empty

    Yeah, it depends on what you mean by "empty."

    I assumed he was after "not yet allocated" but of course you can also allocate an array and assign it no members.

  9. #9
    Addicted Member sergeos's Avatar
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    Re: VB Snippet - Determine if Array is Empty

    I'm using this construction
    Code:
    Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDst As Any, pSrc As Any, ByVal ByteLen As Long)
    
    Public Function ArrayIsInitialized(arr) As Boolean
    
      Dim memVal        As Long
    
      CopyMemory memVal, ByVal VarPtr(arr) + 8, ByVal 4 'get pointer to array
      CopyMemory memVal, ByVal memVal, ByVal 4  'see if it points to an address...
      ArrayIsInitialized = (memVal <> 0)        '...if it does, array is intialized
      
      If ArrayIsInitialized Then ArrayIsInitialized = UBound(arr) >= LBound(arr)
    
    End Function


    but not working under 64bit Excel

    Maybe anyone knows how to change for right syntax?
    Ten Years After - 01 You Give Me Loving

  10. #10
    PowerPoster Elroy's Avatar
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    Re: VB Snippet - Determine if Array is Empty

    Here's mine modified for the VBA. It should work in either 32-bit or 64-bit MS-Office. (Tested on Excel 64-bit.)

    I did take out the PtrAdd function and just directly added. I don't feel that that'll be a problem for 64-bit systems because I seriously doubt the sign-bit will go on for our lifetimes, as a 64-bit address space is huge. However, I'm not sure whether MS-Office 32-bit is Large-Address-Aware or not. If it is, that's a bit of a problem.


    Code:
    
    Public Function IsPtrDimmed(pArray As LongPtr, Optional FailOnZeroNegOne As Boolean = True) As Boolean
        ' Works with all array types (static or dynamic), including UDTs, but with these exceptions:
        '       Excludes BSTR String arrays.  Use IsStrDimmed instead.
        '       Excludes Varants CONTAINING arrays.
        '    Varant arrays (not an array containing a varant) will work fine.
        '    Also fixed-length String arrays (static or dynamic) work just fine.
        '    Object arrays (early or late bound) will work just fine.
        '
        ' Example:  If IsPtrDimmed(ArrPtr(SomeArray())) Then ...
        '
        Dim pSA         As LongPtr
        Dim cDims       As Integer
        Dim cElements   As Long
        '
        If pArray = 0& Then Exit Function                               ' Can happen on String arrays.
        CopyMemory pSA, ByVal pArray, Len(pSA)                          ' De-reference.
        If pSA = 0& Then Exit Function                                  ' Dynamic undimensioned array.
        '
        CopyMemory cDims, ByVal pSA, 2&                                 ' This would be unusual, but just in case.
        '
        CopyMemory cElements, ByVal (pSA + 12& + Len(pSA)), Len(pSA)    ' The first Len(pSA) is used as a proxy for the length of pvData, as they're both LongPtr types.
        If cElements = 0& And FailOnZeroNegOne Then Exit Function       ' Decide what to do about 0 to -1 arrays.
        '
        ' If we fell through to here, we should be looking at an array with elements.
        ' Or, we specified FailOnZeroNegOne=False, and it's one of those.
        IsPtrDimmed = True
    End Function
    
    
    And just a snippet for testing:

    Code:
    
    Sub test()
        Dim a() As Byte
        ReDim a(3) ' Comment this line out to test for "not dimmed".
        Debug.Print IsPtrDimmed(ArrPtr(a))
    End Sub
    
    
    And just for info, here's the SafeArray structure setup for either 32-bit or 64-bit:

    Code:
    
    Type SafeArrayBound
        cElements    As Long
        lLbound      As Long
    End Type
    
    Type SafeArrayType
        cDims        As Integer
        fFeatures    As Integer
        cbElements   As Long
        cLocks       As Long
        pvData       As LongPtr
        rgsabound(0 To cDims - 1) As SafeArrayBound ' This is just for an example.  To run, it must be setup differently.
    End Type
    
    NOTICE: Actually, I see a bug in the above code. I'm going camping later today so I can't fix it right now, but I'll fix it later. I AM digging past that LongPtr to get cElements, so I need to consider whether it's 32-bit or 64-bit.
    EDIT: It's now fixed. The problem was that I'm jumping to the first cElements to see if any are there (and thereby jumping over rgsabound (which might be either 4 or 8 bytes, depending on the bitness). The 12& + Len(pSA) code fixes it, rather than a hardcoded 16&.
    Last edited by Elroy; Oct 24th, 2021 at 05:25 PM.
    Any software I post in these forums written by me is provided “AS IS” without warranty of any kind, expressed or implied, and permission is hereby granted, free of charge and without restriction, to any person obtaining a copy. Please understand that I’ve been programming since the mid-1970s and still have some of that code. My contemporary VB6 project is approaching 1,000 modules. In addition, I have a “VB6 random code folder” that is overflowing. I’ve been at this long enough to truly not know with absolute certainty from whence every single line of my code has come, with much of it coming from programmers under my employ who signed intellectual property transfers. I have not deliberately attempted to remove any licenses and/or attributions from any software. If someone finds that I have inadvertently done so, I sincerely apologize, and, upon notice and reasonable proof, will re-attach those licenses and/or attributions. To all, peace and happiness.

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