Reg.cs

using System;
using static RegSave.Interop;

namespace RegSave
{
    internal class Reg
    {
        public static UIntPtr HKEY_LOCAL_MACHINE = new UIntPtr(0x80000002u);
        public static int KEY_READ = 0x20019;
        public static int KEY_ALL_ACCESS = 0xF003F;
        public static int REG_OPTION_OPEN_LINK = 0x0008;
        public static int REG_OPTION_BACKUP_RESTORE = 0x0004;
        public static int KEY_QUERY_VALUE = 0x1;

        public static void ExportRegKey(string key, string outFile)
        {
            var hKey = UIntPtr.Zero;
            try
            {
                RegOpenKeyEx(HKEY_LOCAL_MACHINE, key, REG_OPTION_BACKUP_RESTORE | REG_OPTION_OPEN_LINK, KEY_ALL_ACCESS, out hKey); //https://docs.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regcreatekeyexa
                RegSaveKey(hKey, outFile, IntPtr.Zero);
                RegCloseKey(hKey);
                Console.WriteLine("Exported HKLM\\{0} at {1}", key, outFile);
            }
            catch (Exception e)
            {
                throw e;
            }
           
        }
    }
}