Windows API Guide: GetAsyncKeyState Function


Declare Function gethostbyname Lib "wsock32.dll" (ByVal name As String) As Long

Platforms

  • Windows 95: Supported.
  • Windows 98: Supported.
  • Windows NT: Requires Windows NT 3.1 or later.
  • Windows 2000: Supported.
  • Windows CE: Requires Windows CE 1.0 or later.

Description & Usage

gethostbyname gets information about a host computer. The computer is identified by its domain name. The information about the host is placed into a HOSTENT structure, a pointer to which is returned by the function. Note that gethostbyname cannot identify a host computer by its IP address string. (To get information about a computer with a particular IP address, use gethostbyaddr instead.)

Return Value

If successful, the function returns a pointer to a HOSTENT structure that contains data about the host. This pointer is only guaranteed to be valid until the next call to a Winsock function. If an error occured, the function returns zero (use WSAGetLastError to get the error code).

Visual Basic-Specific Issues

To access the returned data, use CopyMemory to copy the data referenced by the pointer into a HOSTENT structure allocated by your program. See the example for a demonstration of this.

Parameters

name
The domain name of the network host to get information about. This cannot be an IP address string.

Example

Print the IP address associated with a domain name specified by the user. Winsock is briefly used to resolve the domain name and format a printable IP address string. The user enters the domain name to resolve in text box txtDomain, and the domain name is resolved when the user clicks button cmdGetIP.

To run this example, place a text box named txtDomain and a command button named cmdGetIP on a form window.

' This code is licensed according to the terms and conditions listed here. ' Declarations and such needed for the example: ' (Copy them to the (declarations) section of a module.) Public Type WSADATA wVersion As Integer wHighVersion As Integer szDescription As String * 257 szSystemStatus As String * 129 iMaxSockets As Long iMaxUdpDg As Long lpVendorInfo As Long End Type  Public Declare Function WSAStartup Lib "wsock32.dll" (ByVal wVersionRequested As Integer, lpWSAData _ As WSADATA) As Long Public Declare Function WSACleanup Lib "wsock32.dll" () As Long Public Type HOSTENT h_name As Long h_aliases As Long h_addrtype As Integer h_length As Integer h_addr_list As Long End Type Public Const AF_INET = 2 Public Declare Function gethostbyname Lib "wsock32.dll" (ByVal name As String) As Long Public Declare Function inet_ntoa Lib "wsock32.dll" (ByVal inaddr As Long) As Long Public Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (Destination As Any, Source _ As Any, ByVal length As Long) Public Declare Function lstrlen Lib "kernel32.dll" Alias "lstrlenA" (ByVal lpString As Any) As Long Public Declare Function lstrcpy Lib "kernel32.dll" Alias "lstrcpyA" (ByVal lpString1 As Any, ByVal _ lpString2 As Any) As Long ' Define a relevant API macro. Public Function MAKEWORD(ByVal bLow As Byte, ByVal bHigh As Byte) As Integer MAKEWORD = Val("&H" & Right("00" & Hex(bHigh), 2) & Right("00" & Hex(bLow), 2)) End Function ' *** Place the following code inside the form window. *** Private Sub cmdGetIP_Click() Dim sockinfo As WSADATA  ' information about Winsock Dim hostinfo As HOSTENT  ' information about an Internet host Dim pHostinfo As Long    ' pointer to a HOSTENT structure Dim pIPAddress As Long   ' pointer to an IP address dword Dim ipAddress As Long    ' an IP address, packed into a dword Dim pIPString As Long    ' pointer to an IP address formatted as a string Dim ipString As String   ' holds a human-readable IP address string Dim retval As Long       ' generic return value ' Open up a Winsock session, using version 2.2. retval = WSAStartup(MAKEWORD(2, 2), sockinfo) If retval <> 0 Then Debug.Print "ERROR: Attempt to open Winsock failed: error"; retval Exit Sub End If ' Get information about the domain specified in txtDomain. pHostinfo = gethostbyname(txtDomain.Text) If pHostinfo = 0 Then Debug.Print "Unable to resolve domain name." Else ' Copy the data into a HOSTENT structure. CopyMemory hostinfo, ByVal pHostinfo, Len(hostinfo) If hostinfo.h_addrtype <> AF_INET Then Debug.Print "A non-IP address was returned." Else ' Copy the pointer to the first (and probably only) IP address in the structure. CopyMemory pIPAddress, ByVal hostinfo.h_addr_list, 4 ' Copy the actual IP address. CopyMemory ipAddress, ByVal pIPAddress, 4 ' Convert the IP address into a human-readable string. pIPString = inet_ntoa(ipAddress) ' Copy the result into a string variable. ipString = Space(lstrlen(pIPString)) retval = lstrcpy(ipString, pIPString) ' Print the result: a human-readable IP address. Debug.Print ipString End If End If ' Close the Winsock session. retval = WSACleanup() End Sub

See Also

gethostbyaddr

Category

Winsock

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Last Modified: October 29, 2000
This page is copyright © 2000 Paul Kuliniewicz. Copyright Information Revised October 29, 2000
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Windows API Guide
Windows API Guide - Reference - Volume 1: Version 3.0 For the MS-DOS and PC-DOS Operating Systems
ISBN: B001V0KQIY
EAN: N/A
Year: 1998
Pages: 610

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