RegistryKey.OpenSubKey RegistryKey.OpenSubKey RegistryKey.OpenSubKey Method

Definition

Retrieves the specified subkey.

Overloads

OpenSubKey(String, RegistryKeyPermissionCheck) OpenSubKey(String, RegistryKeyPermissionCheck) OpenSubKey(String, RegistryKeyPermissionCheck)

Retrieves the specified subkey for read or read/write access.

OpenSubKey(String, RegistryKeyPermissionCheck, RegistryRights) OpenSubKey(String, RegistryKeyPermissionCheck, RegistryRights) OpenSubKey(String, RegistryKeyPermissionCheck, RegistryRights)

Retrieves the specified subkey for read or read/write access, requesting the specified access rights.

OpenSubKey(String, RegistryRights) OpenSubKey(String, RegistryRights) OpenSubKey(String, RegistryRights)

Retrieves a subkey with the specified name and .

Available starting in .NET Framework 4.6

OpenSubKey(String) OpenSubKey(String) OpenSubKey(String)

Retrieves a subkey as read-only.

OpenSubKey(String, Boolean) OpenSubKey(String, Boolean) OpenSubKey(String, Boolean)

Retrieves a specified subkey, and specifies whether write access is to be applied to the key.

OpenSubKey(String, RegistryKeyPermissionCheck) OpenSubKey(String, RegistryKeyPermissionCheck) OpenSubKey(String, RegistryKeyPermissionCheck)

Retrieves the specified subkey for read or read/write access.

public:
 Microsoft::Win32::RegistryKey ^ OpenSubKey(System::String ^ name, Microsoft::Win32::RegistryKeyPermissionCheck permissionCheck);
[System.Runtime.InteropServices.ComVisible(false)]
public Microsoft.Win32.RegistryKey OpenSubKey (string name, Microsoft.Win32.RegistryKeyPermissionCheck permissionCheck);
Public Function OpenSubKey (name As String, permissionCheck As RegistryKeyPermissionCheck) As RegistryKey
Parameters
name
String String String

The name or path of the subkey to create or open.

permissionCheck
RegistryKeyPermissionCheck RegistryKeyPermissionCheck RegistryKeyPermissionCheck

One of the enumeration values that specifies whether the key is opened for read or read/write access.

Returns

The subkey requested, or null if the operation failed.

Exceptions

permissionCheck contains an invalid value.

The user does not have the permissions required to read the registry key.

Examples

The following code example creates a subkey containing 100 key/value pairs and closes it. The example opens the subkey with Default, records the time it takes to read all the values, and closes the subkey. The example opens the subkey with ReadSubTree and records the time it takes to read all the values. Finally, the example computes and displays the percentage improvement.

using System;
using Microsoft.Win32;
using System.Diagnostics;

public class Example
{
    public static void Main()
    {
        const int LIMIT = 100;
        RegistryKey cu = Registry.CurrentUser;
        const string testKey = "RegistryKeyPermissionCheckExample";

        Console.WriteLine("Generating {0} key/value pairs.", LIMIT);
        RegistryKey rk = cu.CreateSubKey(testKey);
        for (int i = 0; i < LIMIT; i++)
        {
            rk.SetValue("Key" + i, i);
        }

        rk.Close();

        Stopwatch s = new Stopwatch();

        // On the default setting, security is checked every time
        // a key/value pair is read.
        rk = cu.OpenSubKey(testKey, RegistryKeyPermissionCheck.Default);
        
        s.Start();
        for (int i = 0; i < LIMIT; i++)
        {
            rk.GetValue("Key" + i, i);
        }
        s.Stop();
        rk.Close();
        long delta1 = s.ElapsedTicks;

        s.Reset();

        // When the key is opened with ReadSubTree, security is 
        // not checked when the values are read.
        rk = cu.OpenSubKey(testKey, RegistryKeyPermissionCheck.ReadSubTree);
        
        s.Start();
        for (int i = 0; i < LIMIT; i++)
        {
            rk.GetValue("Key" + i, i);
        }
        s.Stop();
        rk.Close();
        long delta2 = s.ElapsedTicks;

        double faster = (double) (delta1 - delta2) / (double) delta1;
        Console.WriteLine("ReadSubTree is {0}% faster for {1} values.",
            (faster * 100).ToString("0.0"), LIMIT);

        cu.DeleteSubKey(testKey);
    }
}

/* This code example produces output similar to the following:

Generating 100 key/value pairs.
ReadSubTree is 23.4% faster for 100 values.
 */
Imports System
Imports Microsoft.Win32
Imports System.Diagnostics

Public Class Example
    
    Public Shared Sub Main() 

        Const LIMIT As Integer = 100
        Dim cu As RegistryKey = Registry.CurrentUser
        Const testKey As String = "RegistryKeyPermissionCheckExample"
        
        Console.WriteLine("Generating {0} key/value pairs.", LIMIT)
        Dim rk As RegistryKey = cu.CreateSubKey(testKey)

        For i As Integer = 0 To LIMIT
            rk.SetValue("Key" & i, i)
        Next i
        
        rk.Close()
        
        Dim s As New Stopwatch()
        
        ' On the default setting, security is checked every time
        ' a key/value pair is read.
        rk = cu.OpenSubKey(testKey, _
            RegistryKeyPermissionCheck.Default)
        
        s.Start()
        For i As Integer = 0 To LIMIT
            rk.GetValue("Key" & i, i)
        Next i
        s.Stop()
        rk.Close()
        Dim delta1 As Long = s.ElapsedTicks
        
        s.Reset()
        
        ' When the key is opened with ReadSubTree, security is 
        ' not checked when the values are read.
        rk = cu.OpenSubKey(testKey, _
            RegistryKeyPermissionCheck.ReadSubTree)
        
        s.Start()
        For i As Integer = 0 To LIMIT
            rk.GetValue("Key" & i, i)
        Next i
        s.Stop()
        rk.Close()
        Dim delta2 As Long = s.ElapsedTicks
        
        Dim faster As Double = _
            CDbl(delta1 - delta2) * 100.0 / CDbl(delta1)
        Console.WriteLine("ReadSubTree is {0}% faster for {1} values.", _
            faster.ToString("0.0"), LIMIT)
        
        cu.DeleteSubKey(testKey)
    
    End Sub 
End Class 

' This code example produces output similar to the following:
'
'Generating 100 key/value pairs.
'ReadSubTree is 23.4% faster for 100 values.
' 

Remarks

Rather than throwing an exception, this method returns null if the requested key does not exist.

If permissionCheck is RegistryKeyPermissionCheck.ReadWriteSubTree, the key is opened for reading and writing; if permissionCheck is RegistryKeyPermissionCheck.ReadSubTree or RegistryKeyPermissionCheck.Default, the key is opened for reading unless the parent key was opened with RegistryKeyPermissionCheck.ReadWriteSubTree.

In order to use the OpenSubKey method, you must have an instance of the RegistryKey class. To get an instance of RegistryKey, use one of the static members of the Registry class.

Security

RegistryPermission
for the ability to read the specified registry key. Associated enumeration: Read

SecurityPermission
for the ability to access the specified registry key if it is a remote key. Associated enumeration: UnmanagedCode

See Also

OpenSubKey(String, RegistryKeyPermissionCheck, RegistryRights) OpenSubKey(String, RegistryKeyPermissionCheck, RegistryRights) OpenSubKey(String, RegistryKeyPermissionCheck, RegistryRights)

Retrieves the specified subkey for read or read/write access, requesting the specified access rights.

public:
 Microsoft::Win32::RegistryKey ^ OpenSubKey(System::String ^ name, Microsoft::Win32::RegistryKeyPermissionCheck permissionCheck, System::Security::AccessControl::RegistryRights rights);
[System.Runtime.InteropServices.ComVisible(false)]
public Microsoft.Win32.RegistryKey OpenSubKey (string name, Microsoft.Win32.RegistryKeyPermissionCheck permissionCheck, System.Security.AccessControl.RegistryRights rights);
Public Function OpenSubKey (name As String, permissionCheck As RegistryKeyPermissionCheck, rights As RegistryRights) As RegistryKey
Parameters
name
String String String

The name or path of the subkey to create or open.

permissionCheck
RegistryKeyPermissionCheck RegistryKeyPermissionCheck RegistryKeyPermissionCheck

One of the enumeration values that specifies whether the key is opened for read or read/write access.

rights
RegistryRights RegistryRights RegistryRights

A bitwise combination of enumeration values that specifies the desired security access.

Returns

The subkey requested, or null if the operation failed.

Exceptions

permissionCheck contains an invalid value.

rights includes invalid registry rights values.

-or-

The user does not have the requested permissions.

Remarks

Rather than throwing an exception, this method returns null if the requested key does not exist.

If permissionCheck is RegistryKeyPermissionCheck.ReadWriteSubTree, the key is opened for reading and writing; if permissionCheck is RegistryKeyPermissionCheck.ReadSubTree or RegistryKeyPermissionCheck.Default, the key is opened for reading unless the parent key was opened with RegistryKeyPermissionCheck.ReadWriteSubTree.

The access specified for permissionCheck takes precedence over the access specified for rights. For example, if you specify RegistryKeyPermissionCheck.ReadSubTree for permissionCheck and RegistryRights.WriteKey for rights, an attempt to write to the subkey throws an exception.

In order to use the OpenSubKey method, you must have an instance of the RegistryKey class. To get an instance of RegistryKey, use one of the static members of the Registry class.

Security

RegistryPermission
for the ability to read the specified registry key. Associated enumeration: Read

SecurityPermission
for the ability to access the specified registry key if it is a remote key. Associated enumeration: UnmanagedCode

See Also

OpenSubKey(String, RegistryRights) OpenSubKey(String, RegistryRights) OpenSubKey(String, RegistryRights)

Retrieves a subkey with the specified name and .

Available starting in .NET Framework 4.6

public:
 Microsoft::Win32::RegistryKey ^ OpenSubKey(System::String ^ name, System::Security::AccessControl::RegistryRights rights);
[System.Runtime.InteropServices.ComVisible(false)]
public Microsoft.Win32.RegistryKey OpenSubKey (string name, System.Security.AccessControl.RegistryRights rights);
Public Function OpenSubKey (name As String, rights As RegistryRights) As RegistryKey
Parameters
name
String String String

The name or path of the subkey to create or open.

rights
RegistryRights RegistryRights RegistryRights

The rights for the registry key.

Returns

The subkey requested, or null if the operation failed.

Exceptions

The user does not have the permissions required to access the registry key in the specified mode.

Remarks

You must open a key before it can be manipulated with other methods and properties. To modify a key, you must open it with an overload of the OpenSubKey method that allows you to specify write access.

OpenSubKey(String) OpenSubKey(String) OpenSubKey(String)

Retrieves a subkey as read-only.

public:
 Microsoft::Win32::RegistryKey ^ OpenSubKey(System::String ^ name);
public Microsoft.Win32.RegistryKey OpenSubKey (string name);
Public Function OpenSubKey (name As String) As RegistryKey
Parameters
name
String String String

The name or path of the subkey to open as read-only.

Returns

The subkey requested, or null if the operation failed.

Exceptions

The user does not have the permissions required to read the registry key.

Examples

The following code example creates a test key and uses the OpenSubKey method to open it, demonstrating both overloads of the method.

#using <Microsoft.VisualBasic.dll>

using namespace System;
using namespace Microsoft::Win32;
using namespace Microsoft::VisualBasic;

int main()
{
    // Delete and recreate the test key.
    Registry::CurrentUser->DeleteSubKey( L"RegistryOpenSubKeyExample", false );
    RegistryKey ^ rk = Registry::CurrentUser->CreateSubKey( L"RegistryOpenSubKeyExample" );
    rk->Close();

    // Obtain an instance of RegistryKey for the CurrentUser registry
    // root.
    RegistryKey ^ rkCurrentUser = Registry::CurrentUser;

    // Obtain the test key (read-only) and display it.
    RegistryKey ^ rkTest = rkCurrentUser->OpenSubKey( L"RegistryOpenSubKeyExample" );
    Console::WriteLine( L"Test key: {0}", rkTest );
    rkTest->Close();
    rkCurrentUser->Close();

    // Obtain the test key in one step, using the CurrentUser registry
    // root.
    rkTest = Registry::CurrentUser->OpenSubKey( L"RegistryOpenSubKeyExample" );
    Console::WriteLine( L"Test key: {0}", rkTest );
    rkTest->Close();

    // Open the test key in read/write mode.
    rkTest = Registry::CurrentUser->OpenSubKey( L"RegistryOpenSubKeyExample", true );
    rkTest->SetValue( L"TestName", L"TestValue" );
    Console::WriteLine( L"Test value for TestName: {0}", rkTest->GetValue( L"TestName" ) );
    rkTest->Close();

    return 0;
} //Main
using System;
using Microsoft.Win32;
using Microsoft.VisualBasic;

public class Example
{
    public static void Main()
    {
        // Delete and recreate the test key.
        Registry.CurrentUser.DeleteSubKey("RegistryOpenSubKeyExample", false);
        RegistryKey rk = Registry.CurrentUser.CreateSubKey("RegistryOpenSubKeyExample");
        rk.Close();

        // Obtain an instance of RegistryKey for the CurrentUser registry 
        // root. 
        RegistryKey rkCurrentUser = Registry.CurrentUser;

        // Obtain the test key (read-only) and display it.
        RegistryKey rkTest = rkCurrentUser.OpenSubKey("RegistryOpenSubKeyExample");
        Console.WriteLine("Test key: {0}", rkTest);
        rkTest.Close();
        rkCurrentUser.Close();

        // Obtain the test key in one step, using the CurrentUser registry 
        // root.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample");
        Console.WriteLine("Test key: {0}", rkTest);
        rkTest.Close();

        // Open the test key in read/write mode.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample", true);
        rkTest.SetValue("TestName", "TestValue");
        Console.WriteLine("Test value for TestName: {0}", rkTest.GetValue("TestName"));
        rkTest.Close();
    } //Main
} //Example
Imports System
Imports Microsoft.Win32
Imports Microsoft.VisualBasic

Public Class Example
    Public Shared Sub Main()
        ' Delete and recreate the test key.
        Registry.CurrentUser.DeleteSubKey("RegistryOpenSubKeyExample", False)
        Dim rk As RegistryKey = Registry.CurrentUser.CreateSubKey("RegistryOpenSubKeyExample")
        rk.Close

        ' Obtain an instance of RegistryKey for the CurrentUser registry 
        ' root. 
        Dim rkCurrentUser As RegistryKey = Registry.CurrentUser

        ' Obtain the test key (read-only) and display it.
        Dim rkTest As RegistryKey = rkCurrentUser.OpenSubKey("RegistryOpenSubKeyExample")
        Console.WriteLine("Test key: {0}", rkTest)
        rkTest.Close
        rkCurrentUser.Close

        ' Obtain the test key in one step, using the CurrentUser registry 
        ' root.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample")
        Console.WriteLine("Test key: {0}", rkTest)
        rkTest.Close

        ' Obtain the test key in read/write mode.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample", True)
        rkTest.SetValue("TestName", "TestValue")
        Console.WriteLine("Test value for TestName: {0}", rkTest.GetValue("TestName"))
        rkTest.Close
    End Sub 'Main
End Class 'Example

Remarks

You must open a key before it can be manipulated with other methods and properties. To modify a key, you must open it with an overload of the OpenSubKey method that allows you to specify write access, such as the OpenSubKey(String, RegistryKeyPermissionCheck) overload or the OpenSubKey(String, Boolean) overload.

If the specified subkey cannot be found, then null is returned.

In order to use the OpenSubKey method, you must have an instance of RegistryKey. To get an instance of RegistryKey, use the one of the static members of the Registry class.

Security

RegistryPermission
for the ability to read the specified registry key. Associated enumeration: Read

SecurityPermission
for the ability to access the specified registry key if it is a remote key. Associated enumeration: UnmanagedCode

See Also

OpenSubKey(String, Boolean) OpenSubKey(String, Boolean) OpenSubKey(String, Boolean)

Retrieves a specified subkey, and specifies whether write access is to be applied to the key.

public:
 Microsoft::Win32::RegistryKey ^ OpenSubKey(System::String ^ name, bool writable);
public Microsoft.Win32.RegistryKey OpenSubKey (string name, bool writable);
Public Function OpenSubKey (name As String, writable As Boolean) As RegistryKey
Parameters
name
String String String

Name or path of the subkey to open.

writable
Boolean Boolean Boolean

Set to true if you need write access to the key.

Returns

The subkey requested, or null if the operation failed.

Exceptions

The user does not have the permissions required to access the registry key in the specified mode.

Examples

The following code example creates a test key and uses the OpenSubKey method to open it, demonstrating both overloads of the method.

#using <Microsoft.VisualBasic.dll>

using namespace System;
using namespace Microsoft::Win32;
using namespace Microsoft::VisualBasic;

int main()
{
    // Delete and recreate the test key.
    Registry::CurrentUser->DeleteSubKey( L"RegistryOpenSubKeyExample", false );
    RegistryKey ^ rk = Registry::CurrentUser->CreateSubKey( L"RegistryOpenSubKeyExample" );
    rk->Close();

    // Obtain an instance of RegistryKey for the CurrentUser registry
    // root.
    RegistryKey ^ rkCurrentUser = Registry::CurrentUser;

    // Obtain the test key (read-only) and display it.
    RegistryKey ^ rkTest = rkCurrentUser->OpenSubKey( L"RegistryOpenSubKeyExample" );
    Console::WriteLine( L"Test key: {0}", rkTest );
    rkTest->Close();
    rkCurrentUser->Close();

    // Obtain the test key in one step, using the CurrentUser registry
    // root.
    rkTest = Registry::CurrentUser->OpenSubKey( L"RegistryOpenSubKeyExample" );
    Console::WriteLine( L"Test key: {0}", rkTest );
    rkTest->Close();

    // Open the test key in read/write mode.
    rkTest = Registry::CurrentUser->OpenSubKey( L"RegistryOpenSubKeyExample", true );
    rkTest->SetValue( L"TestName", L"TestValue" );
    Console::WriteLine( L"Test value for TestName: {0}", rkTest->GetValue( L"TestName" ) );
    rkTest->Close();

    return 0;
} //Main
using System;
using Microsoft.Win32;
using Microsoft.VisualBasic;

public class Example
{
    public static void Main()
    {
        // Delete and recreate the test key.
        Registry.CurrentUser.DeleteSubKey("RegistryOpenSubKeyExample", false);
        RegistryKey rk = Registry.CurrentUser.CreateSubKey("RegistryOpenSubKeyExample");
        rk.Close();

        // Obtain an instance of RegistryKey for the CurrentUser registry 
        // root. 
        RegistryKey rkCurrentUser = Registry.CurrentUser;

        // Obtain the test key (read-only) and display it.
        RegistryKey rkTest = rkCurrentUser.OpenSubKey("RegistryOpenSubKeyExample");
        Console.WriteLine("Test key: {0}", rkTest);
        rkTest.Close();
        rkCurrentUser.Close();

        // Obtain the test key in one step, using the CurrentUser registry 
        // root.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample");
        Console.WriteLine("Test key: {0}", rkTest);
        rkTest.Close();

        // Open the test key in read/write mode.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample", true);
        rkTest.SetValue("TestName", "TestValue");
        Console.WriteLine("Test value for TestName: {0}", rkTest.GetValue("TestName"));
        rkTest.Close();
    } //Main
} //Example
Imports System
Imports Microsoft.Win32
Imports Microsoft.VisualBasic

Public Class Example
    Public Shared Sub Main()
        ' Delete and recreate the test key.
        Registry.CurrentUser.DeleteSubKey("RegistryOpenSubKeyExample", False)
        Dim rk As RegistryKey = Registry.CurrentUser.CreateSubKey("RegistryOpenSubKeyExample")
        rk.Close

        ' Obtain an instance of RegistryKey for the CurrentUser registry 
        ' root. 
        Dim rkCurrentUser As RegistryKey = Registry.CurrentUser

        ' Obtain the test key (read-only) and display it.
        Dim rkTest As RegistryKey = rkCurrentUser.OpenSubKey("RegistryOpenSubKeyExample")
        Console.WriteLine("Test key: {0}", rkTest)
        rkTest.Close
        rkCurrentUser.Close

        ' Obtain the test key in one step, using the CurrentUser registry 
        ' root.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample")
        Console.WriteLine("Test key: {0}", rkTest)
        rkTest.Close

        ' Obtain the test key in read/write mode.
        rkTest = Registry.CurrentUser.OpenSubKey("RegistryOpenSubKeyExample", True)
        rkTest.SetValue("TestName", "TestValue")
        Console.WriteLine("Test value for TestName: {0}", rkTest.GetValue("TestName"))
        rkTest.Close
    End Sub 'Main
End Class 'Example

Remarks

If the requested key does not exist, this method returns null instead of throwing an exception.

If writable is true, the key will be opened for reading and writing, otherwise, the key will be opened as read-only.

In order to use the OpenSubKey method, you must have an instance of the RegistryKey method. To get an instance of RegistryKey, use one of the static members of the Registry class.

Security

RegistryPermission
for the ability to read the specified registry key. Associated enumeration: Read

SecurityPermission
for the ability to access the specified registry key if it is a remote key. Associated enumeration: UnmanagedCode

See Also

Applies to