How To Obtain the Host IP Address Using Windows Sockets

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Article ID: 160215 - View products that this article applies to.
This article was previously published under Q160215
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This article demonstrates how to obtain the host IP address of the local machine by using the GetHostByName API of the Windows Sockets dll, Wsock32.dll. To obtain the host IP address, you must use GetHostByName in conjunction with GetHostName.


GetHostName returns the standard host name for the local machine. You can use GetHostByName to resolve this name and return a pointer to the HOSTENT structure. This structure contains the host address information.

Step-by-Step Example

  1. Start a new project in Visual Basic. Form1 is created by default.
  2. Place a CommandButton, Command1, on Form1.
  3. Place the following code in the General Declarations section of Form1:

       Private Const WS_VERSION_REQD = &H101
       Private Const WS_VERSION_MAJOR = WS_VERSION_REQD \ &H100 And &HFF&
       Private Const MIN_SOCKETS_REQD = 1
       Private Const SOCKET_ERROR = -1
       Private Const WSADescription_Len = 256
       Private Const WSASYS_Status_Len = 128
       Private Type HOSTENT
           hName As Long
           hAliases As Long
           hAddrType As Integer
           hLength As Integer
           hAddrList As Long
       End Type
       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
           iMaxUdpDg As Integer
           lpszVendorInfo As Long
       End Type
       Private Declare Function WSAGetLastError Lib "WSOCK32.DLL" () As Long
       Private Declare Function WSAStartup Lib "WSOCK32.DLL" (ByVal _
       wVersionRequired as Integer, lpWSAData As WSADATA) As Long
       Private Declare Function WSACleanup Lib "WSOCK32.DLL" () As Long
       Private Declare Function gethostname Lib "WSOCK32.DLL" (ByVal hostname$, _
       ByVal HostLen as Long) as long
       Private Declare Function gethostbyname Lib "WSOCK32.DLL" (ByVal _
       hostname$) As Long
       Private Declare Sub RtlMoveMemory Lib "KERNEL32" (hpvDest As Any, ByVal _
       hpvSource&, ByVal cbCopy&)
       Function hibyte(ByVal wParam As Integer)
           hibyte = wParam \ &H100 And &HFF&
       End Function
       Function lobyte(ByVal wParam As Integer)
           lobyte = wParam And &HFF&
       End Function
       Sub SocketsInitialize()
       Dim WSAD As WSADATA
       Dim iReturn As Integer
       Dim sLowByte As String, sHighByte As String, sMsg As String
           iReturn = WSAStartup(WS_VERSION_REQD, WSAD)
           If iReturn <> 0 Then
               MsgBox "Winsock.dll is not responding."
           End If
           If lobyte(WSAD.wversion) <WS_VERSION_MAJOR Or (lobyte(WSAD.wversion) = _
               WS_VERSION_MAJOR And hibyte(WSAD.wversion) < WS_VERSION_MINOR) Then
               sHighByte = Trim$(Str$(hibyte(WSAD.wversion)))
               sLowByte = Trim$(Str$(lobyte(WSAD.wversion)))
               sMsg = "Windows Sockets version " & sLowByte & "." & sHighByte
               sMsg = sMsg & " is not supported by winsock.dll "
               MsgBox sMsg
           End If
           'iMaxSockets is not used in winsock 2. So the following check is only
           'necessary for winsock 1. If winsock 2 is requested,
           'the following check can be skipped.
           If WSAD.iMaxSockets < MIN_SOCKETS_REQD Then
               sMsg = "This application requires a minimum of "
               sMsg = sMsg & Trim$(Str$(MIN_SOCKETS_REQD)) & " supported sockets."
               MsgBox sMsg
           End If
       End Sub
       Sub SocketsCleanup()
       Dim lReturn As Long
           lReturn = WSACleanup()
           If lReturn <> 0 Then
               MsgBox "Socket error " & Trim$(Str$(lReturn)) & " occurred in Cleanup "
           End If
       End Sub
       Sub Form_Load()
       End Sub
       Private Sub Form_Unload(Cancel As Integer)
       End Sub
       Private Sub Command1_click()
       Dim hostname As String * 256
       Dim hostent_addr As Long
       Dim host As HOSTENT
       Dim hostip_addr As Long
       Dim temp_ip_address() As Byte
       Dim i As Integer
       Dim ip_address As String
           If gethostname(hostname, 256) = SOCKET_ERROR Then
               MsgBox "Windows Sockets error " & Str(WSAGetLastError())
               Exit Sub
               hostname = Trim$(hostname)
           End If
           hostent_addr = gethostbyname(hostname)
           If hostent_addr = 0 Then
               MsgBox "Winsock.dll is not responding."
               Exit Sub
           End If
           RtlMoveMemory host, hostent_addr, LenB(host)
           RtlMoveMemory hostip_addr, host.hAddrList, 4
           MsgBox hostname
           'get all of the IP address if machine is  multi-homed
               ReDim temp_ip_address(1 To host.hLength)
               RtlMoveMemory temp_ip_address(1), hostip_addr, host.hLength
               For i = 1 To host.hLength
                   ip_address = ip_address & temp_ip_address(i) & "."
               ip_address = Mid$(ip_address, 1, Len(ip_address) - 1)
               MsgBox ip_address
               ip_address = ""
               host.hAddrList = host.hAddrList + LenB(host.hAddrList)
               RtlMoveMemory hostip_addr, host.hAddrList, 4
            Loop While (hostip_addr <> 0)
       End Sub
  4. Press the F5 key to run the project.
  5. Click Command1 to obtain the host information.


For additional information, please see the following article in the Microsoft Knowledge Base:

154512 SAMPLE: WINSOCK.EXE: Getting HostAddress Using Windows Sockets


Article ID: 160215 - Last Review: August 23, 2006 - Revision: 2.4
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