Access Violation Exception RegEnumValue - vb.net

Question

I'm using this code to enumerate all values in a registry key.
Private ReadOnly HKeyLocalMachine As New IntPtr(-2147483646)
Private Const KeyQueryValueWow64Key As Integer = &H101
Private Const ErrorNoMoreItems As Integer = &H103
Private Const errorSuccess As Integer = &H0
Dim keyHandle As IntPtr = Nothing
RegOpenKeyEx(HKeyLocalMachine, newPath, 0, KeyQueryValueWow64Key, keyHandle)
If keyHandle = Nothing Then
Return "Error accessing registry key"
End If
Dim index As Integer = 0
Dim valueName As New StringBuilder(1000)
Dim valueLenght As UInteger
Dim valueDataLenght As IntPtr
If RegQueryInfoKey(keyHandle, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, Nothing, valueLenght, valueDataLenght, Nothing, Nothing) = errorSuccess Then
Debug.WriteLine("SUCCESS IN REGQUERYINFOKEY")
End If
Do
returnValue = RegEnumValue(keyHandle, index, valueName, valueLenght, Nothing, Nothing, datalenght, valueDataLenght)
If returnValue = errorSuccess Then
Debug.WriteLine("Success")
End If
index = index + 1
Loop Until returnValue = ErrorNoMoreItems
Here are my API declarations:
<DllImport("advapi32.dll", CharSet:=CharSet.Unicode)> _
Private Shared Function RegOpenKeyEx( _
hKey As IntPtr, _
subKey As String, _
ulOptions As Integer, _
samDesired As Integer, _
ByRef hkResult As IntPtr _
) As Integer
End Function
<DllImport("advapi32.dll", SetLastError:=True)> _
Private Shared Function RegEnumValue( _
ByVal hKey As IntPtr, _
ByVal dwIndex As Integer, _
ByVal lpValueName As StringBuilder, _
ByRef lpcValueName As UInteger, _
ByVal lpReserved As IntPtr, _
ByVal lpType As IntPtr, _
ByVal lpData As IntPtr, _
ByVal lpcbData As IntPtr _
) As Integer
End Function
<DllImport("advapi32.dll")> _
Private Shared Function RegQueryInfoKey( _
hkey As IntPtr, _
ByRef lpClass As StringBuilder, _
ByRef lpcbClass As UInteger, _
lpReserved As IntPtr, _
ByRef lpcSubKeys As UInteger, _
ByRef lpcbMaxSubKeyLen As UInteger, _
ByRef lpcbMaxClassLen As UInteger, _
ByRef lpcValues As UInteger, _
ByRef lpcbMaxValueNameLen As UInteger, _
ByRef lpcbMaxValueLen As IntPtr, _
ByRef lpcbSecurityDescriptor As UInteger, _
lpftLastWriteTime As IntPtr _
) As Integer
End Function
And i'm getting AccessViolationException when i pass the last parameter of RegEnumValue non-null, if i pass a null IntPtr the function succeeds but no data is retrieved, only the name.
I've tried changing the API variables with no luck, the other two functions always succeed.

Answer 1

The reason that the code fails is that you did not initialise valueDataLenght. Incidentally, you mean to name this variable valueDataLength.
You need the IntPtr variable valueDataLength to refer to a DWORD that contains the length of the data buffer. Using IntPtr here makes life difficult for you. I'd declare the parameter like this instead:
ByRef lpcbData As Integer