How to open a WOW64 registry key from a 64-bit .NET application

Question

My .NET application (any-CPU) needs to read a registry value created by a 32-bit program. On 64-bit Windows this goes under the Wow6432Node key in the registry. I have read that you shouldn't hard-code to the Wow6432Node, so what's the right way to access it with .NET?

Dish

Answer 1

In the case where you explicitly need to read a value written by a 32 bit program in a 64 bit program, it's OK to hard code it. Simply because there really is no other option.

I would of course abstract it out to a helper function. For example

public RegistryKey GetSoftwareRoot() {
  var path = 8 == IntPtr.Size 
    ? @"Software\Wow6432Node"
    : @"Software";
  return Registry.CurrentUser.OpenSubKey(path);
}

Ellerd

Warning: MS say that this approach (hardcoding the "Wow6432Node") is not supported. See msdn.microsoft.com/en-us/library/aa384232(VS.85).aspx – Collect

-1: This behavior breaks in Windows 7/Windows Server 2008 R2, as they use Shared Registry Keys instead: msdn.microsoft.com/en-us/library/aa384253(VS.85).aspx – Ineslta

@R. Bemrose, hmm a -1 downvote for an answer which was given before the breaking change was released in RTM. Why not just edit the answer and add a footnote? – Ellerd

@Ellerd I think it's reasonable to downvote answers that lost their usefulness over time. And that rating should eventually reflect an answer's general usefulness, not its history and pedigree. – Mcalpin

Answer 2

If you can change the target .Net version to v4, then you can use the new OpenBaseKey function e.g.

RegistryKey registryKey;
if (Environment.Is64BitOperatingSystem == true)
{
    registryKey = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry64);
}
else
{
    registryKey = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry32);
}

Ceroplastic

This solution work very with with my Win7 64bit + unit testing. Thanks. – Consolation

This is the way to read the registry. WoW6432Node shouldn't be read directly as Microsoft handles this through their API and have said it could change in the future. – Sympathizer

What if you can't change to 4.x? Use the method above? – Marketable

an incorrect answer got 54 votes? these code always access arch-specific native key like HKLM\Software not HKLM\Software\Wow6432Node even on 64-bit os through a 32-bit program. – Zeculon

Answer 3

The correct way would be to call the native registry api and passing the KEY_WOW64_32KEY flag to RegOpenKeyEx/RegCreateKeyEx

Covenanter

It should be noted that this solution is only valid when pinvoking or using C++ code. – Allstar

@Zenox - It is perfectly valid solution even when using a language like C# of course you would be silly to use it. – Thrasonical

Answer 4

Extending Anders's answer, there's a good example of wrapping the resulting handle in a .NET RegistryKey object on Shahar Prish's blog - be sure to read the comments too though.

Note that unvarnished use of the pinvoke.net wrapper of RegOpenKeyEx is fraught with issues.

Watering