How To Associate a File Extension with Your Application (Win32)

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Step-by-Step Example

1. Start Visual Basic for Windows. If Visual Basic is already running, from the File menu (ALT+F, N) choose New Project and create a Standard EXE project. Form1 is created by default.
2. Add the following code to the General Declarations section of Form1:
   

         Option Explicit
   
         Private Declare Function RegCreateKey Lib "advapi32.dll" Alias _
         "RegCreateKeyA" (ByVal hKey As Long, _
                           ByVal lpSubKey As String, _
                           phkResult As Long) As Long
         Private Declare Function RegSetValue Lib "advapi32.dll" Alias _
         "RegSetValueA" (ByVal hKey As Long, _
                    ByVal lpSubKey As String, _
                    ByVal dwType As Long, _
                    ByVal lpData As String, _
                    ByVal cbData As Long) As Long
   
         ' 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&
   
         Private Const HKEY_CLASSES_ROOT = &H80000000
         Private Const MAX_PATH = 260&
         Private 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
   
   						

3. Press ALT+F, V to save the project. Then press F5 to run the program. Click once on the form and exit the application.
4. Run REGEDIT from the Start menu Run option. You will find the .bar and MyApp entries under the HKEY_CLASSES_ROOT key on your local machine.
   

         .bar = MyApp
         MyApp = My Application
           |
            -- Shell
                 |
                  -- open
                       |
                        -- command = c:\mydir\my.exe %1
   
   						

   You can delete these entries using the RegEdit Edit/Delete menu option.