using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace GetWorkGroup
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Using method 5: {0}", GetJoinedWorkGroup()); //returns the correct workgroup name
            Console.ReadKey();
        }
        public static string GetJoinedWorkGroup()
        {
            int result = 0;
            string domain = null;
            IntPtr pDomain = IntPtr.Zero;
            Win32.NetJoinStatus status = Win32.NetJoinStatus.NetSetupUnknownStatus;
            try
            {
                result = Win32.NetGetJoinInformation(null, out pDomain, out status);
                if (result == Win32.ErrorSuccess &&
                    status == Win32.NetJoinStatus.NetSetupWorkgroupName)
                {
                    domain = Marshal.PtrToStringAuto(pDomain);
                }
            }
            finally
            {
                if (pDomain != IntPtr.Zero) Win32.NetApiBufferFree(pDomain);
            }
            if (domain == null) domain = "";
            return domain;
        }
    }
    internal class Win32
    {
        public const int ErrorSuccess = 0;

        [DllImport("Netapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern int NetGetJoinInformation(string server, out IntPtr domain, out NetJoinStatus status);

        [DllImport("Netapi32.dll")]
        public static extern int NetApiBufferFree(IntPtr Buffer);

        public enum NetJoinStatus
        {
            NetSetupUnknownStatus = 0,
            NetSetupUnjoined,
            NetSetupWorkgroupName,
            NetSetupDomainName
        }

    }
}