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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. 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>
