C# Signature:

[DllImport("advapi32.dll", CharSet = CharSet.Unicode, EntryPoint = "RegOpenKeyEx")]
static extern int RegOpenKeyEx(
    UIntPtr hKey,
    string subKey,
    uint options,
    int sam,
    out UIntPtr phkResult );

VB Signature:

Declare Auto Function RegOpenKeyEx Lib "advapi32.dll"  (
   ByVal hKey As IntPtr,
   ByVal lpSubKey As String,
   ByVal ulOptions As Integer,
   ByVal samDesired As Integer,
   ByRef phkResult As Integer
) As Integer

User-Defined Types:

None.

Change Notes:

- Changed IntPtr to UIntPtr:

  When invoking with IntPtr for the handles, you will run into an Overflow. UIntPtr is the right choice.

Notes:

The current managed versions of OpenSubKey do not support read/writing from the different registry "views" on 64-bit operating systems. So, you're forced to the the APIs to accomplish this feat. See the example below for a "drop in" replacement for OpenSubKey

If the function fails, the return value is a nonzero error code defined in Winerror.h. You can use the FormatMessage function with the FORMAT_MESSAGE_FROM_SYSTEM flag to get a generic description of the error.

uint options: reserved, must be zero.

int sam: access mask that specifies the desired access rights to the key.

values for sam:

Const KEY_QUERY_VALUE = &H1
Const KEY_SET_VALUE = &H2
Const KEY_CREATE_SUB_KEY = &H4
Const KEY_ENUMERATE_SUB_KEYS = &H8
Const KEY_NOTIFY = &H10
Const KEY_CREATE_LINK = &H20
Const KEY_WOW64_32KEY = &H200
Const KEY_WOW64_64KEY = &H100
Const KEY_WOW64_RES = &H300

For compatibility with 16-bit versions of Windows only 'RegOpenKey' is available.

Tips & Tricks:

Please add some!!

Sample Code:

Public Enum RegWow64Options As Integer
   None = 0
   KEY_WOW64_64KEY = &H100
   KEY_WOW64_32KEY = &H200
End Enum

Public Enum RegistryRights As Integer
   ReadKey = 131097
   WriteKey = 131078
End Enum

' overloaded, see below
Public Function OpenSubKey(ByVal Name As String) As RegistryKey
   Return OpenSubKey(Name, False, RegWow64Options.None)
End Function

' overloaded, see below
Public Function OpenSubKey(ByVal Name As String, ByVal Writeable As Boolean) As RegistryKey
   Return OpenSubKey(Name, Writeable, RegWow64Options.None)
End Function

' open a SubKey
Public Function OpenSubKey(ByVal Name As String, ByVal Writeable As Boolean, ByVal Options As RegWow64Options) As RegistryKey
   Dim ret, Rights As Integer
   Dim hSubKey As IntPtr

   ' quick sanity check
   If hKey.Equals(IntPtr.Zero) Then
     Throw New ApplicationException("Cannot access a closed registry key")
   End If

   Rights = RegistryRights.ReadKey
   If Writeable Then
     Rights = RegistryRights.WriteKey
   End If

   ' Ignore the 64-bit flags when running from <= Win2k
   If CDbl(Environment.OSVersion.Version.Major & "." & Environment.OSVersion.Version.Minor) <= 5.0 Then
     Options = RegWow64Options.None
   End If

   ret = RegOpenKeyEx(hKey, Name, 0, Rights Or Options, hSubKey)
   If ret <> 0 Then
     Return Nothing
   End If

   Dim ans As New RegistryKey
   ans.hKey = hSubKey
   ans.RegKeyName = Name
   ans.IsRootHive = False
   Return ans
End Function

Alternative Managed API:

Microsoft.Win32.Registry.BaseKeyName.OpenSubKey("[KeyName]")