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Visual Basic SafeArrayGetDim

What value does this API return. i.e. if I want to make sure that an arrray is dimensioned can I write code like

if safearraygetdim(myarray)>0 then
   its okay to go on
end if
3 Solutions
An undimensioned array in VB is a null pointer so that function will cause an exception.  Try this:-

Public Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (ptr() As Any) As Long

This returns the pointer value of the pointer held by an array variable hence:-

IF VarPtrArray(MyArray) > 0 Then
  'Not OK
End If

One major draw back is that is doesn't work with an array of strings.  For that you will need a type library definition.

Mike TomlinsonMiddle School Assistant TeacherCommented:
Or something like...

Option Explicit

Private someArray() As String

Private Sub Command1_Click()
    Dim ub As Long
    ub = safeArrayGetDim(someArray)
    If ub <> -1 Then
        MsgBox "ub = " & ub, vbInformation, "Dimensioned"
        MsgBox "Not Dimensioned"
    End If
End Sub

Private Function safeArrayGetDim(ByVal arr As Variant) As Long
    On Error GoTo notDimmed
    safeArrayGetDim = UBound(arr)
    Exit Function
    safeArrayGetDim = -1
End Function
colindowAuthor Commented:
I think I follow but to presson the specifics safearraygetdim is this in the api

Public Declare Function SafeArrayGetDim Lib "OLEaut32.dll" (ByRef saArray() As Any) As Long

so what is the value for this api function that tells me my array is not dimensioned ?

Does this API call work with arraysof strings? (mine are!)
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Mike TomlinsonMiddle School Assistant TeacherCommented:
Here is an entire discussion on the topic:
colindowAuthor Commented:
Thank you. As it it happens that was the article that started me wondering what the call safearraygetdim actually returns!
    cElements As Long  ' # of elements in the array dimension
    lLbound   As Long  ' lower bounds of the array dimension
End Type

    cDims       As Integer          ' // Count of dimensions in this array.
    fFeatures   As Integer          ' // Flags used by the SafeArray
                                    ' // routines documented below.
    cbElements  As Long             ' // Size of an element of the array.
                                    ' // Does not include size of
                                    ' // pointed-to data.
    cLocks      As Long             ' // Number of times the array has been
                                    ' // locked without corresponding unlock.
    pvData      As Long             ' // Pointer to the data.
    ' Should be sized to cDims:
    rgsabound() As SAFEARRAYBOUND  ' // One bound for each dimension.
End Type
Const VT_BYREF = &H4000&

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (lpDest As Any, lpSource As Any, ByVal cBytes As Long)

Public Function IsArrayDimmed(TheArray As Variant) As Boolean
   Dim lp As Long, VType As Integer
   If Not IsArray(TheArray) Then Exit Function
   Dim nDims As Integer
   CopyMemory ByVal VarPtr(VType), ByVal VarPtr(TheArray), 2
   CopyMemory ByVal VarPtr(lp), ByVal (VarPtr(TheArray) + 8), 4
   If lp = 0 Then Exit Function
   If (VType And VT_BYREF) <> 0 Then CopyMemory ByVal VarPtr(lp), ByVal lp, 4
   If lp = 0 Then Exit Function
   CopyMemory nDims, ByVal lp, 2
   IsArrayDimmed = CBool(nDims)
End Function

Private Sub Command1_Click()
  Dim abArray()
  MsgBox IsArrayDimmed(abArray)
  ReDim abArray(2, 3)
  MsgBox IsArrayDimmed(abArray)
End Sub
colindowAuthor Commented:
I'd still be interested to know what the value that the  safearraygetdim api returns actually meany but between these answersI've got enough to make my program behave as I'd like so i guess thats an answer.
I'll split the points.

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