How To Obtain the Host IP Address Using Windows Sockets

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 32-bit only, for Windows, version 4.0

SUMMARY

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.

MORE INFORMATION

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 WS_VERSION_MINOR = WS_VERSION_REQD 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&, lpWSAData As WSADATA) As Long
      Private Declare Function WSACleanup Lib "WSOCK32.DLL" () As Long
      Private Declare Function gethostname Lib "WSOCK32.DLL" (ByVal hostname$,
      HostLen&) As Long
      Private Declare Function gethostbyname Lib "WSOCK32.DLL" (ByVal
      hostname$) 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
          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
          End If
   
          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
          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
          End If
   
      End Sub
   
      Sub Form_Load()
   
          SocketsInitialize
   
      End Sub
   
      Private Sub Form_Unload(Cancel As Integer)
   
          SocketsCleanup
   
      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
          Else
              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
   
          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) & "."
          Next
          ip_address = Mid$(ip_address, 1, Len(ip_address) - 1)
   
          MsgBox hostname
          MsgBox ip_address
   
      End Sub
   
   

4. Press the F5 key to run the project.

5. Click Command1 to obtain the host information.

REFERENCES

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

   ARTICLE ID: Q154512
   TITLE     : SAMPLE: WINSOCK.EXE: Getting HostAddress Using Windows
               Sockets