Calling Win31API NetQueryDisplayInformation

[Chris van den Heuvel]

I am trying to enumerate the users of a system from within my app (VB.NET)
Not finding any .Net Framework classes to do this I turned to the Win32 API
and NetQueryDisplayInformation. I can't get it to work from within VB.NET
however. I found the following KB article from MS

http://support.microsoft.com/default.aspx?scid=kb;en-us;316318

When I try to convert to .Net I get an object reference not set error when
calling the actual API function....Please help...

Here's my code:

Public Class UserList

'/* definitions and declarations

Private Const NET_USER = 1
Private Const NET_MACHINE = 2|
Private Const NET_GROUP = 3
Private Const ERROR_MORE_DATA = 234
Private Const REQUESTED_ENTRIES = 5
Private Const MAX_PREFERRED_LENGTH = -1

Private lResult As Int32

Private Structure NET_DISPLAY_USER
Dim usri1_name As Int32 'lpwstr
Dim usri1_comment As Int32 'lpwstr
Dim usri1_flags As Int32
Dim usri1_full_name As Int32 'lpwstr
Dim usri1_user_id As Int32
Dim usri1_next_index As Int32
End Structure

Private Structure NET_DISPLAY_GROUP
Dim grpi3_name As Int32 'lpwstr
Dim grpi3_comment As Int32 'lpwstr
Dim grpi3_group_id As Int32
Dim grpi3_attributes As Int32
Dim grpi3_next_index As Int32
End Structure

Private Structure NET_DISPLAY_MACHINE
Dim usri2_name As Int32 'lpwstr
Dim usri2_comment As Int32 'lpwstr
Dim usri2_flags As Int32
Dim usri2_user_id As Int32
Dim usri2_next_index As Int32
End Structure

Private Declare Function NetQueryDisplayInformation Lib "netapi32.dll"
( _
ByVal lpwServername As String, _
ByVal dwLevel As Int32, _
ByVal dwIndex As Int32, _
ByVal dwReqEntries As Int32, _
ByVal dwMaxLength As Int32, _
ByVal pdwNumEntries As Int32, _
ByVal pBuffer As Int32) As Int32

Private Declare Function NetApiBufferFree Lib "netapi32.dll" (ByVal
BufPtr As Int32) As Int32

Private Declare Sub CopyMem Lib "KERNEL32" Alias "RtlMoveMemory" ( _
ByVal hpvDest As Int32, ByVal hpvSource As Int32, ByVal cbCopy As
Int32)

Private Declare Function CopyString Lib "KERNEL32" Alias "lstrcpyW" ( _
ByVal NewString As String, ByVal OldString As Int32) As Int32

Public Sub GetUserNames()

Try

'/* This code enumerates domain users.
Dim pndu() As NET_DISPLAY_USER
Dim pszTemp As String, pszServer As String
Dim pBuffer As Int32
Dim lLevel As Int32
Dim lIndex As Int32
Dim lNumEntries As Int32
Dim lTotalEntries As Int32

pszServer = ""
lIndex = 0
lTotalEntries = 0
lNumEntries = 0

lResult = ERROR_MORE_DATA


'****************************************************************************************
'Here's where I get the object reference not set to an instance of
an object error
lResult = NetQueryDisplayInformation(pszServer, NET_USER, lIndex, _
REQUESTED_ENTRIES, MAX_PREFERRED_LENGTH, lNumEntries, pBuffer)
'****************************************************************************************

Catch ex As Exception
Throw New ApplicationException(ex.Message, ex)

End Try

End Sub

End Class

 

[Crouchie1998]

Try this instead:

http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=3213&lngWId=10

Crouchie1998
BA (HONS) MCP MCSE

 

[Chris van den Heuvel]

Works perfectly....thanks...