[RESOLVED] Best way to determine # of array dimensions?

[Ellis Dee]

Just curious if there is a way to programmatically determine how many dimensions a dynamic array has. eg:

Sub Test()
    Dim varArray As Variant
    Dim lngArray() As Long
    
    Debug.Print ArrayDimensions(varArray) & "," & ArrayDimensions(lngArray)
    ReDim varArray(9)
    ReDim lngArray(9)
    Debug.Print ArrayDimensions(varArray) & "," & ArrayDimensions(lngArray)
    ReDim varArray(9,9)
    ReDim lngArray(9,9)
    Debug.Print ArrayDimensions(varArray) & "," & ArrayDimensions(lngArray)
    Erase varArray, lngArray
    Debug.Print ArrayDimensions(varArray) & "," & ArrayDimensions(lngArray)
End Sub
 
Function ArrayDimensions(pvarArray As Variant) As Long
    ' ???
End Function

Which would ideally look like this in the debug window:

Test
0,0
1,1
2,2
0,0

Any ideas?

[leinad31]

http://www.codeguru.com/vb/gen/vb_mi...cle.php/c7495/

Get the info from the base using copymemory. Wont work with strings array though.

[Logophobic]

How about this?

Function ArrayDimensions(pvarArray As Variant) As Long
  Dim i As Long
  Dim n As Long
  
  On Error GoTo CleanUp
  Do
    i = i + 1
    n = UBound(pvarArray, i)
  Loop
CleanUp:
  ArrayDimensions = i - 1
End Function

[Ellis Dee]

Logo, yeah, that's certainly a functional solution, and is likely the best one.

I'm intrigued by the idea of reading the first two bytes of the array base. From what I can gather, I need to read the safe array pointer from the data section of pvarArray, and then somehow directly access the first two bytes it points to.

Here's what I have so far.

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)
 
Public Function ArrayDimensions(pvarArray As Variant) As Long
    Dim lngPointer As Long ' ???
    
    If VarType(pvarArray) < vbArray Then
        ArrayDimensions = -1
    Else
        CopyMemory lngPointer, pvarArray, 4 ' ???
    End If
End Function

Clearly, I'm way out of my depth.

How do I skip the first 8 bytes of pvarArray and access the four byte (long) safe array pointer directly?

Once I get that pointer, how do I go to where it's pointing and read the two byte (integer) dimension?

Anyone?

[Lord Orwell]

Are you wanting to know the upper and lower bounds, or are you trying to determine how many dimensions it has?
In either case, The shorter the code, the 1)easier to debug 2)faster to run 3)smaller the executable. I would go with his example.

[Paul M]

The shorter the code does not always mean faster to run. Easier to debug of course There was a recent topic regarding arrays which randem done a lot of tests showing time it took to execute the code have a look

[Paul M]

Dimensions of Array

The method there uses the CopyMemory API and it works very well

[Ellis Dee]

Perfect, that's exactly what I was hoping for.

Here's the API solution: (which does work with strings)

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (dest As Any, source As Any, ByVal bytes As Long)

' Returns 0 for unintialized array, -1 for non-array
' Thanks to Francesco Balena of devx.com/vb2themax
Function ArrayDimensionsAPI(pvarArray As Variant) As Long
    Const VT_BYREF = &H4000&
    Dim lngPointer As Long
    Dim intType As Integer
    Dim intDimensions As Integer

    CopyMemory intType, pvarArray, 2
    If (intType And vbArray) <> 0 Then
        ' Get safe array pointer
        CopyMemory lngPointer, ByVal VarPtr(pvarArray) + 8, 4
        ' If not a typed array, pointer is to a pointer, so resolve
        If (intType And VT_BYREF) Then CopyMemory lngPointer, ByVal lngPointer, 4
        ' If array is initialized...
        If lngPointer Then
            ' Read dimension from header of safe array
            CopyMemory intDimensions, ByVal lngPointer, 2
            ArrayDimensionsAPI = intDimensions
        End If
    End If
    ' Distinguish non-arrays (-1) from uninitialized arrays (0)
    If ArrayDimensionsAPI = 0 And Not (VarType(pvarArray) And vbArray) = vbArray Then ArrayDimensionsAPI = -1
End Function

Here's the error trapping solution:

' Returns 0 for unintialized array, -1 for non-array
Function ArrayDimensions(pvarArray As Variant) As Long
    Dim lngTemp As Long
    Dim i As Long
    
    On Error Resume Next
    Do
        i = i + 1
        lngTemp = UBound(pvarArray, i)
        Select Case Err.Number
            Case 13: ArrayDimensions = -1
            Case 9: ArrayDimensions = i - 1
        End Select
    Loop Until Err.Number
End Function

Of course, neither works with UDTs, but just the thought of a multi-dimensional UDT array makes my skin crawl.

[Lord Orwell]

why wouldn't the error method work on a udt array?

[Ellis Dee]

Compile Error:

Only user-defined types defined in public object modules can be coerced to or from a variant or passed to late-bound functions.