Determine path to registry key from HKEY handle in C++

Question

Given a handle to a Windows Registry Key, such as the ones that are set by ::RegOpenKeyEx(), is it possible to determine the full path to that key?

I realize that in

Answer 1

I was excited to find this article and its well liked solution. Until I found that my system's NTDLL.DLL did not have NtQueryKeyType.

After some hunting around, I ran across ZwQueryKey in the DDK forums.

It is in C#, but here is the solution that works for me:

enum KEY_INFORMATION_CLASS
{
    KeyBasicInformation,            // A KEY_BASIC_INFORMATION structure is supplied.
    KeyNodeInformation,             // A KEY_NODE_INFORMATION structure is supplied.
    KeyFullInformation,             // A KEY_FULL_INFORMATION structure is supplied.
    KeyNameInformation,             // A KEY_NAME_INFORMATION structure is supplied.
    KeyCachedInformation,           // A KEY_CACHED_INFORMATION structure is supplied.
    KeyFlagsInformation,            // Reserved for system use.
    KeyVirtualizationInformation,   // A KEY_VIRTUALIZATION_INFORMATION structure is supplied.
    KeyHandleTagsInformation,       // Reserved for system use.
    MaxKeyInfoClass                 // The maximum value in this enumeration type.
}
[StructLayout(LayoutKind.Sequential)]
public struct KEY_NAME_INFORMATION
{
    public UInt32 NameLength;     // The size, in bytes, of the key name string in the Name array.
    public char[] Name;           // An array of wide characters that contains the name of the key.
                                  // This character string is not null-terminated.
                                  // Only the first element in this array is included in the
                                  //    KEY_NAME_INFORMATION structure definition.
                                  //    The storage for the remaining elements in the array immediately
                                  //    follows this element.
}

[DllImport("ntdll.dll", SetLastError = true, CharSet = CharSet.Unicode)]
private static extern int ZwQueryKey(IntPtr hKey, KEY_INFORMATION_CLASS KeyInformationClass, IntPtr lpKeyInformation, int Length, out int ResultLength);

public static String GetHKeyName(IntPtr hKey)
{
    String result = String.Empty;
    IntPtr pKNI = IntPtr.Zero;

    int needed = 0;
    int status = ZwQueryKey(hKey, KEY_INFORMATION_CLASS.KeyNameInformation, IntPtr.Zero, 0, out needed);
    if ((UInt32)status == 0xC0000023)   // STATUS_BUFFER_TOO_SMALL
    {
        pKNI = Marshal.AllocHGlobal(sizeof(UInt32) + needed + 4 /*paranoia*/);
        status = ZwQueryKey(hKey, KEY_INFORMATION_CLASS.KeyNameInformation, pKNI, needed, out needed);
        if (status == 0)    // STATUS_SUCCESS
        {
            char[] bytes = new char[2 + needed + 2];
            Marshal.Copy(pKNI, bytes, 0, needed);
            // startIndex == 2  skips the NameLength field of the structure (2 chars == 4 bytes)
            // needed/2         reduces value from bytes to chars
            //  needed/2 - 2    reduces length to not include the NameLength
            result = new String(bytes, 2, (needed/2)-2);
        }
    }
    Marshal.FreeHGlobal(pKNI);
    return result;
}

I've only ever tried it while running as Administrator, which may be required.

The result is a bit oddly formatted: \REGISTRY\MACHINE\SOFTWARE\company\product for example, instead of HKEY_LOCAL_MACHINE\SOFTWARE\company\product.