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<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 &lt;systemd/sd-id128.h&gt;</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.</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>
