00b67f09dd
Also known as ISC bind. This import adds utilities such as host(1), dig(1), and nslookup(1), as well as many other tools and libraries. Change-Id: I035ca46e64f1965d57019e773f4ff0ef035e4aa3
440 lines
16 KiB
Plaintext
440 lines
16 KiB
Plaintext
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY mdash "—">]>
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<!--
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- Copyright (C) 2004, 2005, 2007, 2014 Internet Systems Consortium, Inc. ("ISC")
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- Copyright (C) 2001 Internet Software Consortium.
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-
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- Permission to use, copy, modify, and/or distribute this software for any
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- purpose with or without fee is hereby granted, provided that the above
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- copyright notice and this permission notice appear in all copies.
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-
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- THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
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- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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- AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
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- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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- OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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- PERFORMANCE OF THIS SOFTWARE.
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-->
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<refentry>
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<refentryinfo>
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<date>June 18, 2007</date>
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</refentryinfo>
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<refmeta>
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<refentrytitle>lwres_gethostent</refentrytitle>
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<manvolnum>3</manvolnum>
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<refmiscinfo>BIND9</refmiscinfo>
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</refmeta>
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<docinfo>
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<copyright>
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<year>2004</year>
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<year>2005</year>
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<year>2007</year>
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<year>2014</year>
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<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
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</copyright>
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<copyright>
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<year>2001</year>
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<holder>Internet Software Consortium.</holder>
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</copyright>
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</docinfo>
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<refnamediv>
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<refname>lwres_gethostbyname</refname>
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<refname>lwres_gethostbyname2</refname>
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<refname>lwres_gethostbyaddr</refname>
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<refname>lwres_gethostent</refname>
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<refname>lwres_sethostent</refname>
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<refname>lwres_endhostent</refname>
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<refname>lwres_gethostbyname_r</refname>
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<refname>lwres_gethostbyaddr_r</refname>
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<refname>lwres_gethostent_r</refname>
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<refname>lwres_sethostent_r</refname>
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<refname>lwres_endhostent_r</refname>
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<refpurpose>lightweight resolver get network host entry</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <lwres/netdb.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostbyname</function></funcdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostbyname2</function></funcdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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<paramdef>int <parameter>af</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostbyaddr</function></funcdef>
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<paramdef>const char *<parameter>addr</parameter></paramdef>
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<paramdef>int <parameter>len</parameter></paramdef>
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<paramdef>int <parameter>type</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostent</function></funcdef>
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<paramdef>void</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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void
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<function>lwres_sethostent</function></funcdef>
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<paramdef>int <parameter>stayopen</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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void
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<function>lwres_endhostent</function></funcdef>
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<paramdef>void</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostbyname_r</function></funcdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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<paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
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<paramdef>char *<parameter>buf</parameter></paramdef>
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<paramdef>int <parameter>buflen</parameter></paramdef>
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<paramdef>int *<parameter>error</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostbyaddr_r</function></funcdef>
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<paramdef>const char *<parameter>addr</parameter></paramdef>
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<paramdef>int <parameter>len</parameter></paramdef>
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<paramdef>int <parameter>type</parameter></paramdef>
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<paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
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<paramdef>char *<parameter>buf</parameter></paramdef>
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<paramdef>int <parameter>buflen</parameter></paramdef>
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<paramdef>int *<parameter>error</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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struct hostent *
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<function>lwres_gethostent_r</function></funcdef>
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<paramdef>struct hostent *<parameter>resbuf</parameter></paramdef>
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<paramdef>char *<parameter>buf</parameter></paramdef>
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<paramdef>int <parameter>buflen</parameter></paramdef>
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<paramdef>int *<parameter>error</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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void
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<function>lwres_sethostent_r</function></funcdef>
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<paramdef>int <parameter>stayopen</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>
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void
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<function>lwres_endhostent_r</function></funcdef>
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<paramdef>void</paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>DESCRIPTION</title>
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<para>
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These functions provide hostname-to-address and
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address-to-hostname lookups by means of the lightweight resolver.
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They are similar to the standard
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<citerefentry>
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<refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>
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</citerefentry>
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functions provided by most operating systems.
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They use a
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<type>struct hostent</type>
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which is usually defined in
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<filename><namedb.h></filename>.
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</para>
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<para><programlisting>
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struct hostent {
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char *h_name; /* official name of host */
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char **h_aliases; /* alias list */
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int h_addrtype; /* host address type */
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int h_length; /* length of address */
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char **h_addr_list; /* list of addresses from name server */
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};
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#define h_addr h_addr_list[0] /* address, for backward compatibility */
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</programlisting>
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</para>
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<para>
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The members of this structure are:
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<variablelist>
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<varlistentry>
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<term><constant>h_name</constant></term>
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<listitem>
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<para>
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The official (canonical) name of the host.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>h_aliases</constant></term>
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<listitem>
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<para>
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A NULL-terminated array of alternate names (nicknames) for the
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host.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>h_addrtype</constant></term>
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<listitem>
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<para>
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The type of address being returned —
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<type>PF_INET</type>
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or
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<type>PF_INET6</type>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>h_length</constant></term>
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<listitem>
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<para>
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The length of the address in bytes.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>h_addr_list</constant></term>
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<listitem>
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<para>
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A <type>NULL</type>
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terminated array of network addresses for the host.
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Host addresses are returned in network byte order.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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For backward compatibility with very old software,
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<constant>h_addr</constant>
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is the first address in
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<constant>h_addr_list.</constant>
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</para>
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<para><function>lwres_gethostent()</function>,
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<function>lwres_sethostent()</function>,
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<function>lwres_endhostent()</function>,
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<function>lwres_gethostent_r()</function>,
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<function>lwres_sethostent_r()</function>
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and
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<function>lwres_endhostent_r()</function>
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provide iteration over the known host entries on systems that
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provide such functionality through facilities like
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<filename>/etc/hosts</filename>
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or NIS. The lightweight resolver does not currently implement
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these functions; it only provides them as stub functions that always
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return failure.
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</para>
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<para><function>lwres_gethostbyname()</function>
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and <function>lwres_gethostbyname2()</function> look up the
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hostname <parameter>name</parameter>.
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<function>lwres_gethostbyname()</function> always looks for an
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IPv4 address while <function>lwres_gethostbyname2()</function>
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looks for an address of protocol family
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<parameter>af</parameter>: either <type>PF_INET</type> or
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<type>PF_INET6</type> — IPv4 or IPV6 addresses
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respectively. Successful calls of the functions return a
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<type>struct hostent</type>for the name that was looked up.
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<type>NULL</type> is returned if the lookups by
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<function>lwres_gethostbyname()</function> or
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<function>lwres_gethostbyname2()</function> fail.
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</para>
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<para>
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Reverse lookups of addresses are performed by
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<function>lwres_gethostbyaddr()</function>.
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<parameter>addr</parameter> is an address of length
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<parameter>len</parameter> bytes and protocol family
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<parameter>type</parameter> — <type>PF_INET</type> or
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<type>PF_INET6</type>.
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<function>lwres_gethostbyname_r()</function> is a
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thread-safe function
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for forward lookups. If an error occurs, an error code is returned in
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<parameter>*error</parameter>.
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<parameter>resbuf</parameter> is a pointer to a
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<type>struct hostent</type> which is initialised by a successful call to
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<function>lwres_gethostbyname_r()</function>.
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<parameter>buf</parameter> is a buffer of length
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<parameter>len</parameter> bytes which is used to store the
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<constant>h_name</constant>, <constant>h_aliases</constant>, and
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<constant>h_addr_list</constant> elements of the
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<type>struct hostent</type> returned in <parameter>resbuf</parameter>.
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Successful calls to <function>lwres_gethostbyname_r()</function>
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return <parameter>resbuf</parameter>,
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which is a pointer to the <type>struct hostent</type> it created.
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</para>
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<para><function>lwres_gethostbyaddr_r()</function>
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is a thread-safe function
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that performs a reverse lookup of address <parameter>addr</parameter>
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which is <parameter>len</parameter> bytes long and is of
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protocol
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family <parameter>type</parameter> — <type>PF_INET</type> or
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<type>PF_INET6</type>. If an error occurs, the error code is returned
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in <parameter>*error</parameter>. The other function
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parameters are
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identical to those in <function>lwres_gethostbyname_r()</function>.
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<parameter>resbuf</parameter> is a pointer to a
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<type>struct hostent</type> which is initialised by a successful call to
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<function>lwres_gethostbyaddr_r()</function>.
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<parameter>buf</parameter> is a buffer of length
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<parameter>len</parameter> bytes which is used to store the
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<constant>h_name</constant>, <constant>h_aliases</constant>, and
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<constant>h_addr_list</constant> elements of the
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<type>struct hostent</type> returned in <parameter>resbuf</parameter>.
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Successful calls to <function>lwres_gethostbyaddr_r()</function> return
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<parameter>resbuf</parameter>, which is a pointer to the
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<function>struct hostent()</function> it created.
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</para>
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</refsect1>
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<refsect1>
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<title>RETURN VALUES</title>
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<para>
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The functions
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<function>lwres_gethostbyname()</function>,
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<function>lwres_gethostbyname2()</function>,
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<function>lwres_gethostbyaddr()</function>,
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and
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<function>lwres_gethostent()</function>
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return NULL to indicate an error. In this case the global variable
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<type>lwres_h_errno</type>
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will contain one of the following error codes defined in
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<filename><lwres/netdb.h></filename>:
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<variablelist>
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<varlistentry>
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<term><constant>HOST_NOT_FOUND</constant></term>
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<listitem>
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<para>
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The host or address was not found.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>TRY_AGAIN</constant></term>
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<listitem>
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<para>
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A recoverable error occurred, e.g., a timeout.
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Retrying the lookup may succeed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>NO_RECOVERY</constant></term>
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<listitem>
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<para>
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A non-recoverable error occurred.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>NO_DATA</constant></term>
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<listitem>
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<para>
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The name exists, but has no address information
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associated with it (or vice versa in the case
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of a reverse lookup). The code NO_ADDRESS
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is accepted as a synonym for NO_DATA for backwards
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compatibility.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para><citerefentry>
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<refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
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</citerefentry>
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translates these error codes to suitable error messages.
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</para>
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<para><function>lwres_gethostent()</function>
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and <function>lwres_gethostent_r()</function>
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always return <type>NULL</type>.
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</para>
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<para>
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Successful calls to <function>lwres_gethostbyname_r()</function> and
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<function>lwres_gethostbyaddr_r()</function> return
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<parameter>resbuf</parameter>, a pointer to the
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<type>struct hostent</type> that was initialised by these functions. They return
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<type>NULL</type> if the lookups fail or if <parameter>buf</parameter>
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was too small to hold the list of addresses and names referenced by
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the <constant>h_name</constant>, <constant>h_aliases</constant>, and
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<constant>h_addr_list</constant> elements of the
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<type>struct hostent</type>.
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If <parameter>buf</parameter> was too small, both
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<function>lwres_gethostbyname_r()</function> and
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<function>lwres_gethostbyaddr_r()</function> set the global
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variable
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<type>errno</type> to <errorcode>ERANGE</errorcode>.
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</para>
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</refsect1>
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<refsect1>
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<title>SEE ALSO</title>
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<para><citerefentry>
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<refentrytitle>gethostent</refentrytitle><manvolnum>3</manvolnum>
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</citerefentry>,
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<citerefentry>
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<refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>
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</citerefentry>,
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<citerefentry>
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<refentrytitle>lwres_hstrerror</refentrytitle><manvolnum>3</manvolnum>
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</citerefentry>
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</para>
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</refsect1>
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<refsect1>
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<title>BUGS</title>
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<para><function>lwres_gethostbyname()</function>,
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<function>lwres_gethostbyname2()</function>,
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<function>lwres_gethostbyaddr()</function>
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and
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<function>lwres_endhostent()</function>
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are not thread safe; they return pointers to static data and
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provide error codes through a global variable.
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Thread-safe versions for name and address lookup are provided by
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<function>lwres_gethostbyname_r()</function>,
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and
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<function>lwres_gethostbyaddr_r()</function>
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respectively.
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</para>
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<para>
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The resolver daemon does not currently support any non-DNS
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name services such as
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<filename>/etc/hosts</filename>
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or
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<type>NIS</type>,
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consequently the above functions don't, either.
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</para>
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</refsect1>
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</refentry><!--
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- Local variables:
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- mode: sgml
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- End:
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-->
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