Access 64-bit HKLM\Software Registry by 32-bit C#.NET Application

Introduction

While running 32-bit Windows application on a 64-bit windows OS, there is a registry redirection. Here, if 32-bit application tries to read a key under HKLM\Software, then due to Registry redirection effective path becomes HKLM\Software\Wow6432Node. For example, we are running 64-bit and 32-bit application to read registry keys as HKLM\Software\xyz and HKLM\Software\Wow6432Node\xyz.

So by default, with an input of HKLM\Software, 64-bit application will read HKLM\Software\xyz while because of registry redirection 32-bit application will read HKLM\Software\Wow6432Node\xyz.

In C#, to read 64-bit HKLM\Software registry keys, we can use RegistryKey.OpenBaseKey method. This method takes two arguments- RegistryHive and RegistryView. Here, seperate registry views are present for 32-bit and 64-bit.

Here is the sample C# code to read AppPaths for 32-bit and 64-bit applications installed on the system:

try
                {
                    string AppPath = @"SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths";
                    RegistryKey rkbase = null;
                    rkbase = RegistryKey.OpenBaseKey
                             (Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry32);
                    using (RegistryKey rk = rkbase.OpenSubKey(uninstallKey))
                    {
                        foreach (string skName in rk.GetSubKeyNames())
                        {
                            using (RegistryKey sk = rk.OpenSubKey(skName))
                            {
                                try
                                {

                                    if (sk.GetValue("Path") != null)
                                    {
                                        //add this to required list
                                    }
                                }
                                catch (Exception ex)
                                {
                                    MessageBox.Show(ex.Message);
                                }
                            }
                        }
                    }

                    if (Environment.Is64BitOperatingSystem)
                    {
                        using (RegistryKey rk = Registry.LocalMachine.OpenSubKey(AppPath))
                        {
                            foreach (string skName in rk.GetSubKeyNames())
                            {
                                using (RegistryKey sk = rk.OpenSubKey(skName))
                                {
                                    try
                                    {
                                        if (sk.GetValue("Path") != null)
                                        {
                                            //add this to required list
                                        }
                                    }
                                    catch (Exception ex)
                                    {
                                        MessageBox.Show(ex.Message);
                                    }
                                }
                            }
                        }
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }

Here, Environment.Is64BitOperatingSystem is used to check if the current system is 64-bit or not. This function is avialable with .NET Framework 4.0.

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