Visual Basic Network Services
gethostbyaddr: Obtain Host Name from IP Address
Posted:   Wed May 03, 2000
Updated:   Monday December 26, 2011
Applies to:   VB4-32, VB5, VB6
Developed with:   VB6, Windows NT4
OS restrictions:   None
Author:   VBnet - Randy Birch


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Network or DUN connection.

Simple function that takes an IP address and returns the host name. You will want to code additional checks to assure that the string passed is a numeric IP.
 BAS Module Code

 Form Code
To a form add a command button (Command1) and two text boxes (Text1 and Text2), along with the following one-liner:

Option Explicit
' Copyright 1996-2011 VBnet/Randy Birch, All Rights Reserved.
' Some pages may also contain other copyrights by the author.
' Distribution: You can freely use this code in your own
'               applications, but you may not reproduce 
'               or publish this code on any web site,
'               online service, or distribute as source 
'               on any media without express permission.
Private Const WSADescription_Len As Long = 256
Private Const WSASYS_Status_Len As Long = 128
Private Const WS_VERSION_REQD As Long = &H101
Private Const IP_SUCCESS As Long = 0
Private Const SOCKET_ERROR As Long = -1
Private Const AF_INET As Long = 2

Private Type WSADATA
  wVersion As Integer
  wHighVersion As Integer
  szDescription(0 To WSADescription_Len) As Byte
  szSystemStatus(0 To WSASYS_Status_Len) As Byte
  imaxsockets As Integer
  imaxudp As Integer
  lpszvenderinfo As Long
End Type

Private Declare Function WSAStartup Lib "wsock32" _
  (ByVal VersionReq As Long, _
   WSADataReturn As WSADATA) As Long
Private Declare Function WSACleanup Lib "wsock32" () As Long

Private Declare Function inet_addr Lib "wsock32" _
  (ByVal s As String) As Long

Private Declare Function gethostbyaddr Lib "wsock32" _
  (haddr As Long, _
   ByVal hnlen As Long, _
   ByVal addrtype As Long) As Long

Private Declare Sub CopyMemory Lib "kernel32" _
   Alias "RtlMoveMemory" _
  (xDest As Any, _
   xSource As Any, _
   ByVal nbytes As Long)
Private Declare Function lstrlen Lib "kernel32" _
   Alias "lstrlenA" _
  (lpString As Any) As Long
Private Sub Command1_Click()

   Text2.Text = GetHostNameFromIP(Text1.Text)
End Sub

Private Function SocketsInitialize() As Boolean

   SocketsInitialize = WSAStartup(WS_VERSION_REQD, WSAD) = IP_SUCCESS
End Function

Private Sub SocketsCleanup()
   If WSACleanup() <> 0 Then
       MsgBox "Windows Sockets error occurred in Cleanup.", vbExclamation
   End If
End Sub

Private Function GetHostNameFromIP(ByVal sAddress As String) As String

   Dim ptrHosent As Long
   Dim hAddress As Long
   Dim nbytes As Long
   If SocketsInitialize() Then

     'convert string address to long
      hAddress = inet_addr(sAddress)
      If hAddress <> SOCKET_ERROR Then
        'obtain a pointer to the HOSTENT structure
        'that contains the name and address
        'corresponding to the given network address.
         ptrHosent = gethostbyaddr(hAddress, 4, AF_INET)
         If ptrHosent <> 0 Then
           'convert address and
           'get resolved hostname
            CopyMemory ptrHosent, ByVal ptrHosent, 4
            nbytes = lstrlen(ByVal ptrHosent)
            If nbytes > 0 Then
               sAddress = Space$(nbytes)
               CopyMemory ByVal sAddress, ByVal ptrHosent, nbytes
               GetHostNameFromIP = sAddress
            End If
            MsgBox "Call to gethostbyaddr failed."
         End If 'If ptrHosent
         MsgBox "String passed is an invalid IP."
      End If 'If hAddress
      MsgBox "Sockets failed to initialize."
   End If  'If SocketsInitialize
End Function


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Copyright 1996-2011 VBnet and Randy Birch. All Rights Reserved.
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