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 = 0; 

               Int32 retVal = WTSEnumerateSessions(serverHandle, 0, 1, ref SessionInfoPtr, ref sessionCount); 

               Int32 dataSize = Marshal.SizeOf(typeof(WTS_SESSION_INFO)); 

               Int32 currentSession = (int)SessionInfoPtr; 

               uint bytes = 0;



               if (retVal != 0) 

               { 

                   for (int i = 0; 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); 

           }



       }



   }