1<?xml version='1.0'?> <!--*-nxml-*--> 2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" 3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> 4<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> 5 6<refentry id="sd_id128_to_string" xmlns:xi="http://www.w3.org/2001/XInclude"> 7 8 <refentryinfo> 9 <title>sd_id128_to_string</title> 10 <productname>systemd</productname> 11 </refentryinfo> 12 13 <refmeta> 14 <refentrytitle>sd_id128_to_string</refentrytitle> 15 <manvolnum>3</manvolnum> 16 </refmeta> 17 18 <refnamediv> 19 <refname>sd_id128_to_string</refname> 20 <refname>SD_ID128_TO_STRING</refname> 21 <refname>SD_ID128_STRING_MAX</refname> 22 <refname>sd_id128_to_uuid_string</refname> 23 <refname>SD_ID128_TO_UUID_STRING</refname> 24 <refname>SD_ID128_UUID_STRING_MAX</refname> 25 <refname>sd_id128_from_string</refname> 26 <refpurpose>Format or parse 128-bit IDs as strings</refpurpose> 27 </refnamediv> 28 29 <refsynopsisdiv> 30 <funcsynopsis> 31 <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> 32 33 <funcsynopsisinfo>#define SD_ID128_STRING_MAX 33U</funcsynopsisinfo> 34 35 <funcsynopsisinfo>#define SD_ID128_UUID_STRING_MAX 37U</funcsynopsisinfo> 36 37 <funcsynopsisinfo>#define SD_ID128_TO_STRING(id) …</funcsynopsisinfo> 38 39 <funcsynopsisinfo>#define SD_ID128_TO_UUID_STRING(id) …</funcsynopsisinfo> 40 41 <funcprototype> 42 <funcdef>char *<function>sd_id128_to_string</function></funcdef> 43 <paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[static SD_ID128_STRING_MAX]</paramdef> 44 </funcprototype> 45 46 <funcprototype> 47 <funcdef>char *<function>sd_id128_uuid_string</function></funcdef> 48 <paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[static SD_ID128_UUID_STRING_MAX]</paramdef> 49 </funcprototype> 50 51 <funcprototype> 52 <funcdef>int <function>sd_id128_from_string</function></funcdef> 53 <paramdef>const char *<parameter>s</parameter>, sd_id128_t *<parameter>ret</parameter></paramdef> 54 </funcprototype> 55 56 </funcsynopsis> 57 </refsynopsisdiv> 58 59 <refsect1> 60 <title>Description</title> 61 62 <para><function>sd_id128_to_string()</function> formats a 128-bit ID as a character string. It expects 63 the ID and a string array capable of storing 33 characters 64 (<constant>SD_ID128_STRING_MAX</constant>). The ID will be formatted as 32 lowercase hexadecimal digits 65 and be terminated by a <constant>NUL</constant> byte.</para> 66 67 <para><function>SD_ID128_TO_STRING()</function> is a macro that wraps 68 <function>sd_id128_to_string()</function> and passes an appropriately sized buffer as second argument, 69 allocated as C99 compound literal. Each use will thus implicitly acquire a suitable buffer on the stack 70 which remains valid until the end of the current code block. This is usually the simplest way to acquire 71 a string representation of a 128-bit ID in a buffer that is valid in the current code block.</para> 72 73 <para><function>sd_id128_to_uuid_string()</function> and <function>SD_ID128_TO_UUID_STRING()</function> 74 are similar to these two functions/macros, but format the 128bit values as RFC4122 UUIDs, i.e. a series 75 of 36 lowercase hexadeciaml digits and dashes, terminated by a <constant>NUL</constant> byte.</para> 76 77 <para><function>sd_id128_from_string()</function> implements the reverse operation: it takes a 33 78 character string with 32 hexadecimal digits (either lowercase or uppercase, terminated by 79 <constant>NUL</constant>) and parses them back into a 128-bit ID returned in 80 <parameter>ret</parameter>. Alternatively, this call can also parse a 37-character string with a 128-bit 81 ID formatted as RFC UUID. If <parameter>ret</parameter> is passed as <constant>NULL</constant> the 82 function will validate the passed ID string, but not actually return it in parsed form.</para> 83 84 <para>Note that when formatting and parsing 36 character UUIDs this is done strictly in Big Endian byte order, 85 i.e. according to <ulink url="https://tools.ietf.org/html/rfc4122">RFC4122</ulink> Variant 1 rules, even 86 if the UUID encodes a different variant. This matches behaviour in various other Linux userspace 87 tools. It's probably wise to avoid UUIDs of other variant types.</para> 88 89 <para>For more information about the <literal>sd_id128_t</literal> type see 90 <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Note that 91 these calls operate the same way on all architectures, i.e. the results do not depend on 92 endianness.</para> 93 94 <para>When formatting a 128-bit ID into a string, it is often easier to use a format string for 95 <citerefentry 96 project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This 97 is easily done using the <constant>SD_ID128_FORMAT_STR</constant> and 98 <function>SD_ID128_FORMAT_VAL()</function> macros. For more information see 99 <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> 100 </refsect1> 101 102 <refsect1> 103 <title>Return Value</title> 104 105 <para><function>sd_id128_to_string()</function> always succeeds and returns a pointer to the string array 106 passed in. <function>sd_id128_from_string()</function> returns 0 on success, in which case 107 <parameter>ret</parameter> is filled in, or a negative errno-style error code.</para> 108 </refsect1> 109 110 <xi:include href="libsystemd-pkgconfig.xml" /> 111 112 <refsect1> 113 <title>See Also</title> 114 115 <para> 116 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, 117 <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>, 118 <citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> 119 </para> 120 </refsect1> 121 122</refentry> 123