How to check if an OCX or DLL is registered using API

How can I check if an OCX or DLL is already registered using API function.

I think that DLLs and OCXs that are registered on a computer have entries in the registry ressembling this one:

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{309A35B5-B3D2-11D5-B13C-00C04F9DA8E7}\InprocServer32

The best way to read this is to loop in the registry "CLSID" key for all subkeys and read each corresponding "InprocServer32" value.

You don't need an API call to see if the file is registered, just use the CreateObject method and check if Object Is Nothing or an error was thrown.
I have included API code to register and unregister DLLs & OCXs

Code:

---

'// These are API calls reqired for registering/unregistering ActiveX DLLs & OCXs  //
Declare Function LoadLibraryRegister _
        Lib "kernel32" Alias "LoadLibraryA" _
        (ByVal lpLibFileName As String) As Long
 
Declare Function CreateThreadForRegister _
        Lib "kernel32" Alias "CreateThread" _
        (lpThreadAttributes As Any, ByVal dwStackSize _
        As Long, ByVal lpStartAddress As Long, _
        ByVal lParameter As Long, ByVal dwCreationFlags As Long, _
        lpThreadID As Long) As Long
 
Declare Function WaitForSingleObject _
        Lib "kernel32" (ByVal hHandle As Long, _
        ByVal dwMilliseconds As Long) As Long
 
Declare Function GetProcAddressRegister _
        Lib "kernel32" Alias "GetProcAddress" _
        (ByVal hModule As Long, ByVal lpProcName As String) _
        As Long

Declare Function FreeLibraryRegister Lib _
        "kernel32" Alias "FreeLibrary" (ByVal hLibModule As Long) _
        As Long

Declare Function CloseHandle Lib "kernel32" _
        (ByVal hObject As Long) As Long

Declare Function GetExitCodeThread Lib "kernel32" _
        (ByVal hThread As Long, lpExitCode As Long) As Long

Declare Sub ExitThread Lib "kernel32" _
        (ByVal dwExitCode As Long)

Public Function RegServer(ByVal FileName As String) As Boolean
'*****************************************************************************
'* Purpose: Registers an ActiveX DLL or OCX.
'*
'* Inputs:  sFile:  ActiveX component to register.
'*
'* Returns: True or false
'*
'*****************************************************************************
    RegServer = RegSvr32(FileName, False)
End Function

Public Function UnRegServer(ByVal FileName As String) As Boolean
'*****************************************************************************
'* Purpose: Unregisters an ActiveX DLL or OCX.
'*
'* Inputs:  sFile:  ActiveX component to unregister.
'*
'* Returns: True or false
'*
'*****************************************************************************
    UnRegServer = RegSvr32(FileName, True)
End Function
   
Private Function RegSvr32(ByVal FileName As String, bUnReg As _
  Boolean) As Boolean

Dim lLib As Long
Dim lProcAddress As Long
Dim lThreadID As Long
Dim lSuccess As Long
Dim lExitCode As Long
Dim lThread As Long
Dim bAns As Boolean
Dim sPurpose As String

sPurpose = IIf(bUnReg, "DllUnregisterServer", _
  "DllRegisterServer")

If Dir(FileName) = "" Then Exit Function

lLib = LoadLibraryRegister(FileName)
'could load file
If lLib = 0 Then Exit Function

lProcAddress = GetProcAddressRegister(lLib, sPurpose)

If lProcAddress = 0 Then
  'Not an ActiveX Component
  FreeLibraryRegister lLib
  Exit Function
Else
  lThread = CreateThreadForRegister(ByVal 0&, 0&, ByVal lProcAddress, ByVal 0&, 0&, lThread)
  If lThread Then
        lSuccess = (WaitForSingleObject(lThread, 10000) = 0)
        If Not lSuccess Then
          Call GetExitCodeThread(lThread, lExitCode)
          Call ExitThread(lExitCode)
          bAns = False
          Exit Function
        Else
          bAns = True
        End If
        CloseHandle lThread
        FreeLibraryRegister lLib
  End If
End If
    RegSvr32 = bAns
End Function

Public Function IsRegistered(sObjectClass As String) As Boolean
'*****************************************************************************
'* Purpose: Checks if an ActiveX DLL or OCX is registered.
'*
'* Inputs:  sObjectClass:  ActiveX component Name.Class
'*
'* Returns: True or false
'*
'*****************************************************************************
    On Error GoTo errHandler

    'Declare a clean object to use
    Dim objCheck As Object
    Dim strResponse As String
   
    Set objCheck = CreateObject(sObjectClass)
    If objCheck Is Nothing Then
        IsRegistered = False
    Else
        IsRegistered = True
    End If
   
    Exit Function

errHandler:
    If Err.Number = 429 Then IsRegistered = False

End Function

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Jerry,

Your IsRegistered function does not seem to work for OCX's.