Microsoft KB Archive/160215

= How To Obtain the Host IP Address Using Windows Sockets =

Article ID: 160215

Article Last Modified on 8/23/2006

-

APPLIES TO


 * Microsoft Visual Basic 5.0 Learning Edition
 * Microsoft Visual Basic 6.0 Learning Edition
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 6.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition
 * Microsoft Visual Basic 4.0 Standard Edition
 * Microsoft Visual Basic 4.0 Professional Edition
 * Microsoft Visual Basic 4.0 32-Bit Enterprise Edition

-



This article was previously published under Q160215



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
 Start a new project in Visual Basic. Form1 is created by default. Place a CommandButton, Command1, on Form1.  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  Press the F5 key to run the project. Click Command1 to obtain the host information.

