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How To Obtain the Host IP Address Using Windows Sockets

This article was previously published under Q160215
SUMMARY
This article demonstrates how to obtain the host IP address of the localmachine by using the GetHostByName API of the Windows Sockets dll,Wsock32.dll. To obtain the host IP address, you must use GetHostByName inconjunction with GetHostName.
MORE INFORMATION
GetHostName returns the standard host name for the local machine. You canuse GetHostByName to resolve this name and return a pointer to the HOSTENTstructure. 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 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       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       '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       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$(hostname)       End If       hostent_addr = gethostbyname(hostname)       If hostent_addr = 0 Then           MsgBox "Winsock.dll is not responding."           Exit Sub       End If       RtlMoveMemory host, hostent_addr, LenB(host)       RtlMoveMemory hostip_addr, host.hAddrList, 4       MsgBox hostname       'get all of the IP address if machine is  multi-homed       Do           ReDim temp_ip_address(1 To host.hLength)           RtlMoveMemory temp_ip_address(1), hostip_addr, host.hLength           For i = 1 To host.hLength               ip_address = ip_address & temp_ip_address(i) & "."           Next           ip_address = Mid$(ip_address, 1, Len(ip_address) - 1)           MsgBox 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.
REFERENCES
For additional information, please see the following article in theMicrosoft Knowledge Base:

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

Article ID: 160215 - Last Review: 08/23/2006 03:52:07 - Revision: 2.4

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