Winsock2 call : gethostbyname() in Visual Basic

Posted on 1998-06-11
Last Modified: 2013-11-25
the socket call gethostbyname() have the following

struct hostent FAR *
    const char FAR * name
so it involves returning a pointer to a UDT, how do I do this in Visual Basic?
I can return the value as BYTE, that doesn't seem to get
me anymore.
any code will be appreciated.
Question by:platiumstar

Expert Comment

ID: 1463110
Check out MSKB #Q160215 located at:

Basically here's the declares and calls:
Private Declare Function gethostname Lib "WSOCK32.DLL" (ByVal hostname$, HostLen&) As Long
Private Declare Function gethostbyname Lib "WSOCK32.DLL" (ByVal hostname$) As Long

   Dim hostname As String * 256
   Dim hostent_addr As Long
  If gethostname(hostname, 256) = SOCKET_ERROR Then
    MsgBox "Windows Sockets error " & Str(WSAGetLastError())
    Exit Sub
    hostname = Trim$(hostname)
  End If
  hostent_addr = gethostbyname(hostname)


Author Comment

ID: 1463111
You're returning a long, where does that get me? I want the HOSTENT structure it returned. Maybe You misunderstood the question.


Expert Comment

ID: 1463112
He had it right, but the pasted text from that article got cut. Rather than me just repaste it here, you should go to the URL clifABB gave, it has an entire example program that does precisely what you want. hostent_addr is a long which holds a pointer to the HOSTENT structure which is then passed to  RtlMoveMemory to copy the structure returned from gethostbyname() into a UDT.

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Accepted Solution

yowkee earned 50 total points
ID: 1463113
You need to use API RtlMoveMemory to copy the pointer
to structure into UDT in VB:

Public Type HOSTENT
    hName As Long
    hAliases As Long
    hAddrType As Integer
    hLength As Integer
    hAddrList As Long
End Type
Public Declare Function gethostbyname Lib _
    "WSOCK32.DLL" (ByVal hostname$) As Long
Public Declare Sub RtlMoveMemory Lib _
    "KERNEL32" (hpvDest As Any, ByVal hpvSource&, ByVal cbCopy&)

    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

    :   ' Getting host name

    hostent_addr = gethostbyname(hostname)
    If hostent_addr = 0 Then
        MsgBox "Winsock.dll is not responding."
        Exit Sub
    End If

    ' Copy to HOSTENT structure
    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) & "."
    ip_address = Left$(ip_address, Len(ip_address) - 1)
    MsgBox ip_address



Author Comment

ID: 1463114
ohhh, ok, stupid me. I guess ClifABB deserve some points. But I like alamo's comment better, explain things. oh well. more points next time.

Author Comment

ID: 1463115
ohhh, ok, stupid me. I guess ClifABB deserve some points. But I like alamo's comment better, explain things. oh well. more points next time. Thanks to all.

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