Option Explicit
 
Public Const REG_SZ As Long = 1
Public Const REG_DWORD As Long = 4
Public Const HKEY_CLASSES_ROOT = &H80000000
Public Const HKEY_CURRENT_USER = &H80000001
Public Const HKEY_LOCAL_MACHINE = &H80000002
Public Const HKEY_USERS = &H80000003
 
Public Const ERROR_NONE = 0
Public Const ERROR_BADDB = 1
Public Const ERROR_BADKEY = 2
Public Const ERROR_CANTOPEN = 3
Public Const ERROR_CANTREAD = 4
Public Const ERROR_CANTWRITE = 5
Public Const ERROR_OUTOFMEMORY = 6
Public Const ERROR_INVALID_PARAMETER = 7
Public Const ERROR_ACCESS_DENIED = 8
Public Const ERROR_INVALID_PARAMETERS = 87
Public Const ERROR_NO_MORE_ITEMS = 259
 
Public Const KEY_ALL_ACCESS = &H3F
Public Const REG_OPTION_NON_VOLATILE = 0
 
Public Declare Function RegCloseKey Lib "advapi32.dll" _
                        (ByVal hKey As Long) As Long
 
Public Declare Function RegCreateKeyEx _
    Lib "advapi32.dll" Alias "RegCreateKeyExA" _
   (ByVal hKey As Long, _
    ByVal lpSubKey As String, _
    ByVal Reserved As Long, _
    ByVal lpClass As String, _
    ByVal dwOptions As Long, _
    ByVal samDesired As Long, _
    ByVal lpSecurityAttributes As Long, _
    phkResult As Long, _
    lpdwDisposition As Long) As Long
 
Public Declare Function RegOpenKeyEx _
    Lib "advapi32.dll" Alias "RegOpenKeyExA" _
   (ByVal hKey As Long, _
    ByVal lpSubKey As String, _
    ByVal ulOptions As Long, _
    ByVal samDesired As Long, _
    phkResult As Long) As Long
 
Public Declare Function RegSetValueExString _
    Lib "advapi32.dll" Alias "RegSetValueExA" _
   (ByVal hKey As Long, _
    ByVal lpValueName As String, _
    ByVal Reserved As Long, _
    ByVal dwType As Long, _
    ByVal lpValue As String, _
    ByVal cbData As Long) As Long
 
Public Declare Function RegSetValueExLong _
   Lib "advapi32.dll" Alias "RegSetValueExA" _
  (ByVal hKey As Long, _
   ByVal lpValueName As String, _
   ByVal Reserved As Long, _
   ByVal dwType As Long, _
   lpValue As Long, _
   ByVal cbData As Long) As Long

Public Sub CreateAssociation()

    Dim sPath As String

    ' File Associations begin with a listing of the default extension
    ' under HKEY_CLASSES_ROOT.  So the first step is to create that
    ' root extension item
    CreateNewKey ".xxx", HKEY_CLASSES_ROOT

    ' To the extension just added, add a subitem where the registry
    ' will look for commands relating to the .xxx extension
    ' ("MyApp.Document"). Its type is String (REG_SZ)
    SetKeyValue ".xxx", "", "MyApp.Document", REG_SZ

    ' Create the 'MyApp.Document item under HKEY_CLASSES_ROOT. 
    ' This is where you'll put the command line to execute or 
    ' other shell statements necessary.
    CreateNewKey "MyApp.Document\shell\open\command", _
                 HKEY_CLASSES_ROOT

    ' Set its default item to "MyApp Document".  This is what is 
    ' displayed in Explorer against for files with a xxx extension.
    ' Its type is String (REG_SZ)
    SetKeyValue "MyApp.Document", "", "MyApp Document", REG_SZ

    ' Finally, add the path to myapp.exe.   Remember to add %1 as
    ' the final command parameter to assure the app opens the 
    ' passed command line item.
    ' (results in '"c:\LongPathname\Myapp.exe %1").   Again, its
    ' type is string.
    sPath = "c:\LongPathname\Myapp.exe %1"
    SetKeyValue "MyApp.Document\shell\open\command", "", _
                sPath, REG_SZ
    'All done
    MsgBox "The file association has been made!"   

End Sub