deleting a 64 bit registry entry from a 32 bit app in c#.

Okay, this may be old hat to some of you, but it took me some time to figure it out and I didn’t find much useful when searching.

Came across a need to delete a 64 bit registry value from a 32 bit app.  The standard registry delete functions would end up deleting it from the Wow6432Node, which was what was not the desired outcome.

The code to make it happen is pretty simple, but I’ve got no error checking in the sample code here:

First, the P/Invoke stuff:

[DllImport("advapi32.dll")]

static extern int RegOpenKeyEx(

    RegistryHive hKey,

    [MarshalAs(UnmanagedType.VBByRefStr)] ref string subKey,

    int options,

    int sam,

    out UIntPtr phkResult);

[DllImport("advapi32.dll")]

static extern int RegDeleteValue(

    UIntPtr hKey,

    [MarshalAs(UnmanagedType.VBByRefStr)] ref string lpValueName

);

And then, the meat of the program:

UIntPtr KeyHandle = UIntPtr.Zero;

string key = @"Software\Microsoft\Windows NT\CurrentVersion\TestKey";

string value = "DeleteThisValue";

RegOpenKeyEx(RegistryHive.LocalMachine, ref key, 0, 0x000f013f, out KeyHandle);

RegDeleteValue(KeyHandle, ref value);

The magic numbers 0 and 0x000f103f shouldn’t be hardcoded; the 0 is “Non-volatile registry” and the hex number is both “KEY_WOW64_64KEY” (0x100) and “KEY_ALL_ACCESS (0xf003f)”.