How to Access 64-bit Registry Keys from a 32-bit .NET Application?

Accessing 64-bit Registry Entries from a 32-bit .NET Application

Accessing the 64-bit registry from a 32-bit application running on a 64-bit Windows system requires a specific approach. Fortunately, the .NET Framework 4.x and later versions offer built-in support for this.

Leveraging RegistryView for 64-bit Registry Access

The RegistryView enumeration is key to differentiating between 32-bit and 64-bit registry access. Here's how to use it:

<code class="language-csharp">// Access the 64-bit registry
using Microsoft.Win32;

RegistryKey localKey64 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64);
RegistryKey sqlServerKey64 = localKey64.OpenSubKey(@"SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL");

// Access the 32-bit registry
RegistryKey localKey32 = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32);
RegistryKey sqlServerKey32 = localKey32.OpenSubKey(@"SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL");</code>

Retrieving Specific Registry Values

To retrieve a specific value, such as "SQLEXPRESS" under the "Instance NamesSQL" key, use:

<code class="language-csharp">string sqlExpressKeyName = (string)sqlServerKey64.GetValue("SQLEXPRESS");</code>

Comprehensive Key Retrieval: Combining 32-bit and 64-bit Results

For situations needing data from both 32-bit and 64-bit registry locations, a combined query is beneficial:

<code class="language-csharp">using System.Linq;

IEnumerable<string> GetAllRegValueNames(string regPath)
{
    var reg64 = GetRegValueNames(RegistryView.Registry64, regPath);
    var reg32 = GetRegValueNames(RegistryView.Registry32, regPath);
    var result = (reg64 != null && reg32 != null) ? reg64.Union(reg32) : (reg64 ?? reg32);
    return (result ?? new List<string>().AsEnumerable()).OrderBy(x => x);
}</code>

Where GetRegValueNames is a helper function (not shown, but easily implemented) that retrieves value names under a given key. regPath specifies the registry path.

Example usage:

<code class="language-csharp">
var sqlRegPath = @"SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL";
foreach (var keyName in GetAllRegValueNames(sqlRegPath))
{
    Console.WriteLine(keyName);
}
```  This iterates through all found keys, regardless of whether they reside in the 32-bit or 64-bit registry hive.</code>

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