CopyMemory Function

[James_B]

What do you think, for instance, about the below? Is it dangerous, inefficient, or what? (I've made the input and output of the OverlayStr function variant because I want to build it up so it can handle strings, doubles, and genuine variants).

Edit: Actually, it's far from safe, so don't run it without saving your work! But I'm not sure quite why...

Option Explicit
Public pLB1 As Long, pUB1 As Long
Public pLB2 As Long, pUB2 As Long
Public pnElmts As Long
Private Type SABnd
    nElmts As Long
    nLBnd As Long
End Type
Private Type SafeArr          'http://msdn.microsoft.com/en-us/library/ms221482.aspx
    nDims As Integer          'ArrayPtr +0: number of dimensions
    fFlags As Integer         '         +2: see link
    nBytes As Long            '         +4: number of bytes per array item
    nLocks As Long            '         +8: whether or not array is locked
    nPtrTo1stElmt As Long     '        +12: pointer to first element in array
    nBnds(0 To 1) As SABnd    '        +16: pointer to last dim's count & LBound structure
End Type                      '             stored in right to left order
Sub SetBndVars(v As Variant)
   pLB2 = -1: pUB2 = -1
   pLB1 = LBound(v, 1): pUB1 = UBound(v, 1)
   On Error Resume Next
      pLB2 = LBound(v, 2): pUB2 = UBound(v, 2)
   On Error GoTo 0
   If pLB1 < pUB1 Or pLB2 = -1 Then
      pnElmts = pUB1 - pLB1 + 1
   Else
      pnElmts = pUB2 - pLB2 + 1
   End If
End Sub
Sub TestStr()
   Dim s() As String
   ReDim s(0 To 10, 1 To 1)
   Dim i As Long
      For i = 0 To 10
         s(i, 1) = "ZZZZZZZZ"
      Next i
   Dim sRes() As String
   sRes = OverlayStr(s)
End Sub
Function OverlayStr(v As Variant) As Variant
   SetBndVars v
   Dim LngOverlay() As Long
   Dim vPtr As Long
   'Let vPtr be the location of the [long] pointer in the variant
   CopyMemory vPtr, ByVal VarPtr(v) + 8&, 4&
   'Find out where that pointer is pointing to:
   CopyMemory vPtr, ByVal vPtr, 4&
   '...and this is where we put the overlay, so
   Dim SA As SafeArr
   With SA                                            'i.e. the new array description
      .nBytes = 4                                     'bytes per array item
      .nDims = 1                                      'number of dimensions
      CopyMemory .nPtrTo1stElmt, ByVal vPtr + 12&, 4& 'location of 1st element in array
      .nBnds(0).nElmts = pnElmts
      .nBnds(0).nLBnd = 1
   End With
   CopyMemory ByVal VarPtrArray(LngOverlay), VarPtr(SA), 4&
   Dim s() As String
   ReDim s(1 To UBound(LngOverlay))
   CopyMemory ByVal VarPtr(s(1)), LngOverlay(1), 4& * UBound(LngOverlay)
   OverlayStr = s
   CopyMemory ByVal VarPtrArray(LngOverlay), 0&, 4& ' release overlay
   ZeroMemory ByVal vPtr + 12&, 4& * UBound(s)
End Function