[VB6] Problem Using CopyMemory API to Get Collection Keys

[jbarnett74]

Thanks everyone! I took LaVolpe's suggestion to zero out the tColElem when the loop ends. I also refactored some code based on Bonnie's suggestions. However, I don't think I implemented Bonnie's suggestion correctly, because it seemed to strip the keys from the collection.

As for credit to whomever came up with the structure declarations, I have no idea. I'm glad my question benefited others and wish I could give credit where it's due, but there are no comments in the code I'm working with to explain where it came from. I imagine the person who implemented the code in my application copied it from elsewhere, because the code style was inconsistent with the majority of the application.

I'm ok with the extra step to extract the key, so here's the working solution that I've implemented:

Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)
Private Declare Function lstrlenW Lib "kernel32" (ByVal lpString As Any) As Long

Private Type CollectionData
    Unk0(0 To 2) As Long
    Unk1 As Long
    ElementCount As Long
    Unk2 As Long
    PtrFirstElement As Long
    PtrLastElement As Long
    Unk3 As Long
    Unk4 As Long
    Unk5 As Long
End Type

Private Type CollectionElement
    Data As Variant
    Key As String
    PtrPrev As Long
    PtrNext As Long
    Unk0 As Long
    Unk1 As Long
    Unk2 As Long
End Type

Public Function GetKeys(ByVal oCollection As Collection) As String()
    Dim asKeys() As String
    Dim lIdx As Long
    Dim tColl As CollectionData
    Dim tColElem As CollectionElement
    Dim tNulldata() As Byte
    Dim sKey As String
    
    If oCollection.Count > 0 Then
        ReDim tNulldata(1 To LenB(tColElem))
        ReDim asKeys(0 To oCollection.Count - 1)
        CopyMemory tColl, ByVal ObjPtr(oCollection), LenB(tColl)
        tColElem.PtrNext = tColl.PtrFirstElement
        For lIdx = 0 To tColl.ElementCount - 1
            CopyMemory tColElem, ByVal tColElem.PtrNext, LenB(tColElem)

            sKey = String$(lstrlenW(tColElem.Key), 0)
            CopyMemory ByVal StrPtr(sKey), ByVal tColElem.Key, lstrlenW(tColElem.Key) * 2

            asKeys(lIdx) = sKey
        Next
        CopyMemory tColElem, tNulldata(1), UBound(tNulldata)
    End If
    
    GetKeys = asKeys
End Function