How to Associate a File Extension with Your Application

• Professional and Enterprise Editions of Microsoft Visual Basic, 16-bit only, version 4.0, for Windows

SUMMARY

If your application makes use of data files and processes command-line arguments, you may want to associate the extension of your application's data file with your executable program name by modifying the REG.DAT file.

MORE INFORMATION

You can make modifications to the REG.DAT file by calling the RegCreateKey& and RegSetValue& application programming interface (API) functions.

Step-by-Step Example

1. Start Visual Basic for Windows. If Visual Basic is already running, choose New Project from the File menu (ALT+F, N). Form1 is created by default.

2. Add the following code to the general declarations section of Form1, taking care to enter each Declare statement on one single line:

   Private Declare Function RegCreateKey& Lib "SHELL.DLL" (ByVal hKey&, _
   

Private Declare Function RegSetValue& Lib "SHELL.DLL" (ByVal hKey&, _ ByVal

   ' Return codes from Registration functions.
   Const ERROR_SUCCESS = 0&
   Const ERROR_BADDB = 1&
   Const ERROR_BADKEY = 2&
   Const ERROR_CANTOPEN = 3&
   Const ERROR_CANTREAD = 4&
   Const ERROR_CANTWRITE = 5&
   Const ERROR_OUTOFMEMORY = 6&
   Const ERROR_INVALID_PARAMETER = 7&
   Const ERROR_ACCESS_DENIED = 8&

   Const HKEY_CLASSES_ROOT = 1
   Const MAX_PATH = 256&
   Const REG_SZ = 1

   Private Sub Form_Click ()

     Dim sKeyName As String   'Holds Key Name in registry.
     Dim sKeyValue As String  'Holds Key Value in registry.
     Dim ret&           'Holds error status if any from API calls.
     Dim lphKey&        'Holds created key handle from RegCreateKey.

     'This creates a Root entry called "MyApp".
     sKeyName = "MyApp"
     sKeyValue = "My Application"
     ret& = RegCreateKey&(HKEY_CLASSES_ROOT, sKeyName, lphKey&)
     ret& = RegSetValue&(lphKey&, "", REG_SZ, sKeyValue, 0&)

     'This creates a Root entry called .BAR associated with "MyApp".
     sKeyName = ".bar"
     sKeyValue = "MyApp"
     ret& = RegCreateKey&(HKEY_CLASSES_ROOT, sKeyName, lphKey&)
     ret& = RegSetValue&(lphKey&, "", REG_SZ, sKeyValue, 0&)

     'This sets the command line for "MyApp".
     sKeyName = "MyApp"
     sKeyValue = "c:\mydir\my.exe %1"
     ret& = RegCreateKey&(HKEY_CLASSES_ROOT, sKeyName, lphKey&)
     ret& = RegSetValue&(lphKey&, "shell\open\command", REG_SZ, sKeyValue,
     MAX_PATH)

   End Sub