Late binding of a DLL

[CBrianA]

I have a program that can be used in an environment where the end user may or may not have Novell libraries installed. I need to have one program that has conditional compilation, so when I build, the program will either have live subroutines that call the Novell libraries, or stubs.

The problem is that the full program has a Novell component (nwdirauth.dll) that will be missing on some systems. I would like to be able to use the conditional compilation switches so that the compiler might include the component, as long as I had set the switch.

Or, if it is possible, use late binding in the live novell subroutines, so that the routine would perform a createobject on the DLL, so it can be referenced without adding the component at build time.

This is a major piece of my project. Please help!

[LaVolpe]

Which language? VB6, VB.net or something else?

If nwdirauth.dll is an activeX dll, you should be able to do late binding. If the user's system doesn't have the DLL, are you distributing it? If so, use early binding and include the DLL to the setup package. Maybe I might be misunderstanding the scenarios.

Welcome to the forums.

[CBrianA]

Yes, my apologies - it is VB6.


The DLL is not something that I will be distributing - I just want to use it if it is present and registered.

[Hack]

Then try something like

Private Declare Function SearchTreeForFile Lib "imagehlp" _
(ByVal RootPath As String, _
ByVal InputPathName As String, _
ByVal OutputPathBuffer As String) As Long

Private Const MAX_PATH = 260
Private blnIsFound As Boolean

Private Sub Form_Load()
    Dim BufferString As String
    Dim FindIt As Long
    'create a buffer string
    BufferString = String(MAX_PATH, 0)
    'Typically, FindIt will return 1 if successfull, 0 if not
    FindIt = SearchTreeForFile("c:\", "nwdirauth.dll" , BufferString)
    If FindIt <> 0 Then
        blnIsFound = True
    End If
End Sub

Now you can wrap your use of this library in an If blnIsFound = True structure.

[LaVolpe]

Hack's method will work, using LoadLibrary will be faster, assuming the DLL is a standard vs Active-X DLL. If Active-X, then CreateObject with error checking can be faster than a search. Determining if the DLL is there or not, isn't a major problem.

The search method will not inform you if it is installed or not

Private Declare Function LoadLibrary Lib "kernel32.dll" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
Private Declare Function FreeLibrary Lib "kernel32.dll" (ByVal hLibModule As Long) As Long

    
    ' only works if DLL is non-ActiveX (standard)
    Dim lb As Long
    lb = LoadLibrary("nwdirauth.dll")
    If lb Then
        FreeLibrary lb
        ' it exists and is registered
    Else
        ' doesn't exist in DLL path or not registered
    End If
    
    ' only works if DLL is an Active-X DLL
    On Error Resume Next
    Dim tObject As Object ' late binding
    Set tObject = CreateObject([class name], [server name])
    If tObject Is Nothing Then
        ' doesn't exist or not registered
    Else
        ' it exists & is registered
       ' set to nothing or set to public variable
      ' and in your routines, you can check if the public variable is Nothing before trying to use it
    End If