List connected users–similar to task manager

class Program
   {
       [DllImport("wtsapi32.dll")]
       static extern IntPtr WTSOpenServer([MarshalAs(UnmanagedType.LPStr)] String pServerName);

       [DllImport("wtsapi32.dll")]
       static extern void WTSCloseServer(IntPtr hServer);

       [DllImport("wtsapi32.dll")]
       static extern Int32 WTSEnumerateSessions(
           IntPtr hServer,
           [MarshalAs(UnmanagedType.U4)] Int32 Reserved,
           [MarshalAs(UnmanagedType.U4)] Int32 Version,
           ref IntPtr ppSessionInfo,
           [MarshalAs(UnmanagedType.U4)] ref Int32 pCount);

       [DllImport("wtsapi32.dll")]
       static extern void WTSFreeMemory(IntPtr pMemory);

       [DllImport("Wtsapi32.dll")]
       static extern bool WTSQuerySessionInformation(
           System.IntPtr hServer, int sessionId, WTS_INFO_CLASS wtsInfoClass, out System.IntPtr ppBuffer, out uint pBytesReturned);

       [StructLayout(LayoutKind.Sequential)]
       private struct WTS_SESSION_INFO
       {
           public Int32 SessionID;

           [MarshalAs(UnmanagedType.LPStr)]
           public String pWinStationName;

           public WTS_CONNECTSTATE_CLASS State;
       }

       public enum WTS_INFO_CLASS
       {
           WTSInitialProgram,
           WTSApplicationName,
           WTSWorkingDirectory,
           WTSOEMId,
           WTSSessionId,
           WTSUserName,
           WTSWinStationName,
           WTSDomainName,
           WTSConnectState,
           WTSClientBuildNumber,
           WTSClientName,
           WTSClientDirectory,
           WTSClientProductId,
           WTSClientHardwareId,
           WTSClientAddress,
           WTSClientDisplay,
           WTSClientProtocolType
       }
       public enum WTS_CONNECTSTATE_CLASS
       {
           WTSActive,
           WTSConnected,
           WTSConnectQuery,
           WTSShadow,
           WTSDisconnected,
           WTSIdle,
           WTSListen,
           WTSReset,
           WTSDown,
           WTSInit
       }

       static void Main(string[] args)
       {
           ListUsers(Environment.MachineName);
           Console.ReadKey();
       }

       public static IntPtr OpenServer(String Name)
       {
           IntPtr server = WTSOpenServer(Name);
           return server;
       }
       public static void CloseServer(IntPtr ServerHandle)
       {
           WTSCloseServer(ServerHandle);
       }
       public static void ListUsers(String ServerName)
       {
           IntPtr serverHandle = IntPtr.Zero;
           List<String> resultList = new List<string>();
           serverHandle = OpenServer(ServerName);

           try
           {
               IntPtr SessionInfoPtr = IntPtr.Zero;
               IntPtr userPtr = IntPtr.Zero;
               IntPtr domainPtr = IntPtr.Zero;
               Int32 sessionCount = ;
               Int32 retVal = WTSEnumerateSessions(serverHandle, , , ref SessionInfoPtr, ref sessionCount);
               Int32 dataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO));
               Int32 currentSession = (int)SessionInfoPtr;
               uint bytes = ;

               if (retVal != )
               {
                   for (int i = ; i < sessionCount; i++)
                   {
                       WTS_SESSION_INFO si = (WTS_SESSION_INFO)Marshal.PtrToStructure((System.IntPtr)currentSession, typeof(WTS_SESSION_INFO));
                       currentSession += dataSize;

                       WTSQuerySessionInformation(serverHandle, si.SessionID, WTS_INFO_CLASS.WTSUserName, out userPtr, out bytes);
                       WTSQuerySessionInformation(serverHandle, si.SessionID, WTS_INFO_CLASS.WTSDomainName, out domainPtr, out bytes);

                       Console.WriteLine(string.Format("SessionID : {0} Domain : {1} User : {2} StationName : {3} State : {4}",
                           si.SessionID, Marshal.PtrToStringAnsi(domainPtr), Marshal.PtrToStringAnsi(userPtr), si.pWinStationName, si.State));

                       WTSFreeMemory(userPtr);
                       WTSFreeMemory(domainPtr);
                   }

                   WTSFreeMemory(SessionInfoPtr);
               }
           }
           finally
           {
               CloseServer(serverHandle);
           }

       }

   }