Question

I’m trying to develop a c# program to print the entire tree of LocalMachine to the console. So far I’ve just been able to get the subkeys of HKEY_LOCAL_MACHINE, but nothing deeper than that. I’m relatively sure I need to use some kind of recursion here to get all the contents of subkeys and their subkeys, and so on. I’m just not sure how to go about it. Here’s what I’ve got as of now:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Win32;

namespace PrintLocalMachine
{
    class PrintLocalMachine
    {
        static void Main(string[] args)
        {
            Console.Out.WriteLine(Registry.LocalMachine.Name);
            string[] subkeynames = Registry.LocalMachine.GetSubKeyNames();            

            foreach (string subkey in subkeynames)
            {
                try
                {
                    RegistryKey rk = Registry.LocalMachine.OpenSubKey(subkey);
                    Console.Out.WriteLine(rk.Name);

                    string[] subkeynames2 = rk.GetSubKeyNames();

                    foreach (string s in subkeynames2)
                    {
                        recurse(s, rk);
                    }
                }
                catch (Exception e) { }
            }
        }

        private static void recurse(string sub, RegistryKey rk)
        {
            RegistryKey rk2 = Registry.LocalMachine.OpenSubKey(sub);
            Console.Out.WriteLine(rk2.Name);

            string[] subkeynames3 = rk.GetSubKeyNames();

            foreach(string s2 in subkeynames3){
                recurse(s2, rk2);
            }
        }
    }
}

Could someone explain how I should go about this? I really just need to be pointed in the right direction, I’ve just hit a wall with this.

EDIT: I changed a bit and updated the code; the updated code is hanging on HKEY_CURRENT_MACHINE\SAM, just printing it over and over until StackOverflowException

Answer 1

You are right. This kind of problem where you have a structure inside a structure can be solved through recursion. What you need to do is write a recursive function i.e. a function that calls itself until a certain condition satisfies. In this case that condition would be that if a Registry Key has at least one child we need to go inside that Registry Key and we will continue to do so until we reach a leaf node i.e. a Registry Key which has no more children.

 private static void Main(string[] args)
    {

        string[] subkeynames = Registry.LocalMachine.GetSubKeyNames();
        Console.Out.WriteLine(Registry.LocalMachine.Name);

        foreach (string subkey in subkeynames)
        {
            try
            {
                //this might raise a security exception
                RegistryKey rk = Registry.LocalMachine.OpenSubKey(subkey);
                recurse(rk);
                rk.Close();
            }
            catch (Exception e)
            {
                Console.Write("Couldnt access key : " + subkey + "\n " + e.ToString());
            }
        }

        Console.ReadKey();
    }

    private static void recurse(RegistryKey rk)
    {
        Console.WriteLine(rk.Name);
        string[] subkeys = rk.GetSubKeyNames();

        if (null != subkeys && subkeys.Count() > 0)
        {
            foreach (var subkey in subkeys)
            {
                try
                {
                    //this might raise a security exception
                    RegistryKey key = rk.OpenSubKey(subkey);
                    recurse(key);
                }
                catch (Exception e)
                {
                    Console.Write("Couldnt access key : " + subkey + "\n " + e.ToString());
                }

            }
        }
    }