03 May 2022

C# - Read Windows registry keys

Reading Windows registry keys using C# should be straight forward. Or is it?

How to read Windows registry keys using C#

While you can use Microsoft.Win32.Registry to read and write keys, sometimes you can get caught out. When a 32-bit application runs on a 64-bit OS, it will by default look at HKEY_LOCAL_MACHINE\Software\Wow6432Node.

Wow6432Node Registry Key

The below section is courtesy of the Advanced Installer website

The Wow6432Node registry entry indicates that you are running a 64-bit Windows version.

The operating system uses this key to display a separate view of HKEY_LOCAL_MACHINE\SOFTWARE for 32-bit applications that run on 64-bit Windows versions. When a 32-bit application writes or reads a value under the HKEY_LOCAL_MACHINE\SOFTWARE<company><product> subkey, the application reads from the HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node<company><product> subkey.

A registry reflector copies certain values between the 32-bit and 64-bit registry views (mainly for COM registration) and resolves any conflicts using a “last-writer-wins” approach.


Let’s look at a couple of examples to clarify this.

Let’s say you have a registry subkey HKEY_LOCAL_MACHINE\Software\MyCustomApp with key MyCustomKey, type REG_SZ, value=TRUE. In this case, the code you would normally use to read this subkey is:

var subKey = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(@"SOFTWARE\MyCustomApp1");

However, if it is a 32-bit application running in a 64-bit OS, var subKey will return null. Instead you will need to append the path to the below.

subKey = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(@"SOFTWARE\WOW6432Node\MyCustomApp1");

Alternatively, in the below code you can specify either RegistryView.Registry32 (for 32-bit) or RegistryView.Registry64 (for 64-bit) as the second parameter to get the right value .

using (Microsoft.Win32.RegistryKey hklm32 = 
    using (var subKey = hklm32.OpenSubKey(@"SOFTWARE\MyCustomApp"))
        if (subKey != null)
            var keyValue = subKey.GetValue("MyCustomKey");

If you use RegistryView.Registry64 you will be reading from HKEY_LOCAL_MACHINE\Software\MyCustomApp mentioned in the first example.