How To Use the WTSEnumerateSessions Terminal Server Function from Visual Basic (291789)

MORE INFORMATION

The WTSEnumerateSessions function is used to retrieve session information on a Terminal Server. As a result, it requires Windows 2000 Server that is running Terminal Services or Windows NT 4.0 Service Pack 4 (SP4) or later, Terminal Server Edition. This sample enumerates the sessions on a specified Terminal Server and displays the information in the Immediate window of the Visual Basic Integrated Development Environment (IDE).

You can use the WTSEnumerateSessions function to retrieve the session ID, computer name, and session state. The code sample queries the Terminal Server computer that the code runs on, but it can be modified to query sessions that are running on other Terminal Servers. You must have Query Information permission to query a Terminal Server. For more information, see the MSDN documentation in the "References" section.

Step-by-Step Example

1. Create a new Standard EXE project in Visual Basic. Form1 is created by default.
2. Add a CommandButton control (Command1) to Form1.
3. Paste the following code into the code window of Form1:

   Option Explicit
   
   Private Const WTS_CURRENT_SERVER_HANDLE = 0&
   
   Private Enum WTS_CONNECTSTATE_CLASS
       WTSActive
       WTSConnected
       WTSConnectQuery
       WTSShadow
       WTSDisconnected
       WTSIdle
       WTSListen
       WTSReset
       WTSDown
       WTSInit
   End Enum
   
   Private Type WTS_SESSION_INFO
       SessionID As Long
       pWinStationName As Long
       state As WTS_CONNECTSTATE_CLASS
   End Type
   
   Private Declare Function WTSEnumerateSessions _
       Lib "wtsapi32.dll" Alias "WTSEnumerateSessionsA" ( _
       ByVal hServer As Long, ByVal Reserved As Long, _
       ByVal Version As Long, ByRef ppSessionInfo As Long, _
       ByRef pCount As Long _
       ) As Long
       
   Private Declare Sub WTSFreeMemory Lib "wtsapi32.dll" ( _
       ByVal pMemory As Long)
   
   Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _
       Destination As Any, Source As Any, ByVal length As Long)
   
   Private Declare Function lstrlenA Lib "kernel32" ( _
       ByVal lpString As String) As Long
   
   Private Declare Function lstrcpy Lib "kernel32" Alias "lstrcpyA" ( _
       ByVal lpString1 As String, ByVal lpString2 As Long) As Long
   
   Private arrWTSSessions() As WTS_SESSION_INFO
   
   Private Function GetWTSSessions() As WTS_SESSION_INFO()
       Dim RetVal As Long
       Dim lpBuffer As Long
       Dim Count As Long
       Dim p As Long
       Dim arrSessionInfo() As WTS_SESSION_INFO
       
       RetVal = WTSEnumerateSessions(WTS_CURRENT_SERVER_HANDLE, _
                                      0&, _
                                      1, _
                                      lpBuffer, _
                                      Count)
       If RetVal Then
           ' WTSEnumerateProcesses was successful.
           
           p = lpBuffer
           ReDim arrSessionInfo(Count - 1)
           CopyMemory arrSessionInfo(0), ByVal p, _
              Count * LenB(arrSessionInfo(0))
           ' Free the memory buffer.
           WTSFreeMemory lpBuffer
       
        Else
           ' Error occurred calling WTSEnumerateProcesses.
           ' Check Err.LastDllError for error code.
           MsgBox "An error occurred calling WTSEnumerateProcesses.  " & _
           "Check the Platform SDK error codes in the MSDN Documentation " & _
           "for more information.", vbCritical, "ERROR " & Err.LastDllError
       End If
       GetWTSSessions = arrSessionInfo
   End Function
   
   Private Sub Command1_Click()
       Dim i As Integer
       
       arrWTSSessions = GetWTSSessions
       For i = LBound(arrWTSSessions) To UBound(arrWTSSessions)
           Debug.Print "Session ID: " & arrWTSSessions(i).SessionID
           Debug.Print "Machine Name: " & _
              PointerToStringA(arrWTSSessions(i).pWinStationName)
           Debug.Print "Connect State: " & arrWTSSessions(i).state
           Debug.Print "***********"
       Next i
   End Sub
   
   Public Function PointerToStringA(ByVal lpStringA As Long) As String
      Dim nLen As Long
      Dim sTemp As String
   
      If lpStringA Then
         nLen = lstrlenA(ByVal lpStringA)
         If nLen Then
            sTemp = String(nLen, vbNullChar)
            lstrcpy sTemp, ByVal lpStringA
            PointerToStringA = sTemp
         End If
      End If
   End Function
   					

4. Press the F5 key to run the project.
5. Make sure that the Immediate window is open. If not, press CTRL+G to open it. Click Command1. The session information is displayed in the Immediate window.