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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_id128_to_string">
<refentryinfo>
<title>sd_id128_to_string</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd_id128_to_string</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_id128_to_string</refname>
<refname>sd_id128_from_string</refname>
<refpurpose>Format or parse 128-bit IDs as strings</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo>
<funcprototype>
<funcdef>char *<function>sd_id128_to_string</function></funcdef>
<paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[33]</paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_from_string</function></funcdef>
<paramdef>const char *<parameter>s</parameter>, sd_id128_t *<parameter>ret</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_id128_to_string()</function> formats a 128-bit
ID as a character string. It expects the ID and a string array
capable of storing 33 characters. The ID will be formatted as 32
lowercase hexadecimal digits and be terminated by a
<constant>NUL</constant> byte.</para>
<para><function>sd_id128_from_string()</function> implements the reverse operation: it takes a 33 character string
with 32 hexadecimal digits (either lowercase or uppercase, terminated by <constant>NUL</constant>) and parses them
back into a 128-bit ID returned in <parameter>ret</parameter>. Alternatively, this call can also parse a
37-character string with a 128-bit ID formatted as RFC UUID. If <parameter>ret</parameter> is passed as NULL the
function will validate the passed ID string, but not actually return it in parsed form.</para>
<para>For more information about the <literal>sd_id128_t</literal>
type see
<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Note that these calls operate the same way on all architectures,
i.e. the results do not depend on endianness.</para>
<para>When formatting a 128-bit ID into a string, it is often
easier to use a format string for
<citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
This is easily done using the
<function>SD_ID128_FORMAT_STR</function> and
<function>SD_ID128_FORMAT_VAL()</function> macros. For more
information see
<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para><function>sd_id128_to_string()</function> always succeeds
and returns a pointer to the string array passed in.
<function>sd_id128_from_string</function> returns 0 on success, in
which case <parameter>ret</parameter> is filled in, or a negative
errno-style error code.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>The <function>sd_id128_to_string()</function> and
<function>sd_id128_from_string()</function> interfaces are
available as a shared library, which can be compiled and linked to
with the
<literal>libsystemd</literal> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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