How to use Telnet in a Visual Basic project

Network Component provides an easy-to-use development interface to a variety of IP protocols. By using Network Component, you can very easily create or enhance applications with network features.

Network Component features the following: DNS, FTP, HTTP, HTTPs, ICMP Ping, IP-to-Country, MSN, NTP, RSH, SCP, SFTP, SNMP v1/v2c (Get, GetNext, Set), SNMP Traps, SNMP MIB, SSH, TCP, Telnet, TFTP, UDP, Telnet, Wake-On-LAN and more.

Network Component can be well integrated into any development platform that supports ActiveX objects.

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Step 1: Download and install the Network Component

Download Network Component from the ActiveXperts Download Site and start the installation. The installation guides you through the installation process.

Step 2: Create a new Visual Basic project

Launch 'Microsoft Visual Basic' from the Start menu, and choose 'New' from the 'File Menu'. The 'New Project' dialog appears.
Select 'Standard Exe' and click 'OK':

Step 3: Refer to the Network Component Library and create the objects

A new Project is created, with a blank form.

First, you must add a reference to Network Component in the project to be able to use the object. To do so, choose 'References...' from the 'Project' menu. In the 'References' dialog that pops up, enable the 'Network Component 3.1 Type Library' reference as shown in the following picture:

Click 'OK' to close the 'References...' dialog.

Then, select the Project form and choose 'View Code' from the context menu:

On top of your code, declare the following object:

Public objTcp As AxNetwork.Tcp

Step 4: Create the object

From the Code window, select 'Form'. The Private Sub 'Form_Load()' will be displayed now. In the 'Form Load' function, create the object in the following way:

Set objTcp = CreateObject("AxNetwork.Tcp")

Appendix: Full source code

Option Explicit

Dim objSocket As Tcp
Dim objConstants As NwConstants

Private Declare Function GetTempPath Lib "kernel32" Alias "GetTempPathA" (ByVal nBufferLength As Long, ByVal lpBuffer As String) As Long
Private Const MAX_PATH = 260

Dim isConnected As Boolean


'///////////////////////////////////////////////////////////////////////

Private Sub Form_Load()
    Set objSocket = CreateObject("AxNetwork.Tcp")
    Set objConstants = CreateObject("AxNetwork.NwConstants")
    
    objSocket.Protocol = objConstants.nwSOCKET_PROTOCOL_TELNET
    isConnected = False
    SetDefaultLogFile
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub btnConnect_Click()
    objSocket.LogFile = txtLogFile.Text
    objSocket.Connect txtHost, CInt(txtPort.Text)
    
    If (ShowResult() = 0) Then
        isConnected = True
        EnableControls
    End If
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub btnDisconnect_Click()
    objSocket.Disconnect
    
    If (ShowResult() = 0) Then
        isConnected = False
        EnableControls
    End If
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub Timer_Timer()
    While objSocket.HasData
        txtReceived.Text = txtReceived & objSocket.ReceiveString & vbCrLf
    Wend
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub EnableControls()
        btnSubmit.Enabled = isConnected
        btnDisconnect.Enabled = isConnected
        btnConnect.Enabled = Not isConnected
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub btnSubmit_Click()
    objSocket.SendString txtCommand
    
    ShowResult
End Sub

'///////////////////////////////////////////////////////////////////////

Private Sub btnView_Click()
    If FileExists(txtLogFile.Text) = True Then
        Shell "notepad " + txtLogFile.Text, vbNormalFocus
    End If
End Sub

'///////////////////////////////////////////////////////////////////////

Public Function FileExists(sFileName As String) As Boolean
  FileExists = CBool(Len(Dir$(sFileName))) And CBool(Len(sFileName))
End Function

'///////////////////////////////////////////////////////////////////////

Private Function SetDefaultLogFile()
    Dim Buffer As String
    Buffer = Space(MAX_PATH)
    
    If GetTempPath(MAX_PATH, Buffer) <> 0 Then
        txtLogFile.Text = Left$(Buffer, InStr(Buffer, vbNullChar) - 1) & "Telnet.log"
    Else
        txtLogFile.Text = "C:\Telnet.log"
    End If
End Function

'///////////////////////////////////////////////////////////////////////

Private Function ShowResult()
    ShowResult = objSocket.LastError
    txtResult.Caption = ShowResult & ": " & objSocket.GetErrorDescription(ShowResult)
End Function

'///////////////////////////////////////////////////////////////////////

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You can download the complete samples here. There are many other working Network Component scripts on our site and shipped with the product.

NOTE: Demo Projects are created with Microsoft Visual Studio 2008

The Network Component project ships with a set of Microsoft Visual Studio .NET samples, including samples for Microsoft Visual C# .NET. The projects are created with Microsoft Visual Studio 2008.

Users with a later version of Microsoft Visual Studio can open such a project. The Visual Studio Conversion Wizard will guide you through the process of converting the project to the version used.