How Can a 32-bit Application Access the 64-bit Registry in Windows?

Accessing the 64-bit Registry from a 32-bit Windows Application

Challenge:

32-bit applications face difficulties accessing the 64-bit registry on 64-bit Windows systems. This issue often arises when accessing system information residing in the 64-bit registry, such as the path to a SQL Express instance, from a 32-bit unit test running on a 64-bit build server.

Solution:

Accessing the 64-bit Registry:

The RegistryView.Registry64 property provides the solution for accessing the 64-bit registry from a 32-bit application. The following code demonstrates this:

RegistryKey localKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64);
RegistryKey sqlServerKey = localKey.OpenSubKey(@"SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL");
string sqlExpressKeyName = (string)sqlServerKey.GetValue("SQLEXPRESS");

Accessing the 32-bit Registry:

Conversely, to access the 32-bit registry, use RegistryView.Registry32:

RegistryKey localKey32 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32);
RegistryKey sqlServerKey32 = localKey32.OpenSubKey(@"SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL");
string sqlExpressKeyName = (string)sqlServerKey32.GetValue("SQLEXPRESS");

Important Considerations:

• While the 32-bit registry is accessible via the "Wow6432Node" within the 64-bit registry, using RegistryView.Registry32 is the recommended and more direct approach.
• A known bug in Windows 7 (64-bit) may cause the RegisteredOrganization value to incorrectly return "Microsoft" when accessed from 32-bit code. The 64-bit code will return the correct organization.
• The GetAllRegValueNames() function allows retrieval of all key names and values, regardless of registry view (32-bit or 64-bit).
• Utilize the null-coalescing operator (??) to gracefully handle potential null values.

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