sd-id128: add compound literal love to sd_id128_to_string() + id128_to_uuid_string()

1 files changed, 40 insertions, 33 deletions

diff --git a/man/sd_id128_to_string.xml b/man/sd_id128_to_string.xml
index 469768050b..db64bc018d 100644
--- a/man/sd_id128_to_string.xml
+++ b/man/sd_id128_to_string.xml
@@ -17,7 +17,9 @@
 
   <refnamediv>
     <refname>sd_id128_to_string</refname>
+    <refname>SD_ID128_TO_STRING</refname>
     <refname>sd_id128_from_string</refname>
+    <refname>SD_ID128_STRING_MAX</refname>
     <refpurpose>Format or parse 128-bit IDs as strings</refpurpose>
   </refnamediv>
 
@@ -25,9 +27,13 @@
     <funcsynopsis>
       <funcsynopsisinfo>#include &lt;systemd/sd-id128.h&gt;</funcsynopsisinfo>
 
+      <funcsynopsisinfo>#define SD_ID128_STRING_MAX 33U</funcsynopsisinfo>
+
+      <funcsynopsisinfo>#define SD_ID128_TO_STRING(id) …</funcsynopsisinfo>
+
       <funcprototype>
         <funcdef>char *<function>sd_id128_to_string</function></funcdef>
-        <paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[33]</paramdef>
+        <paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[static SD_ID128_STRING_MAX]</paramdef>
       </funcprototype>
 
       <funcprototype>
@@ -41,47 +47,48 @@
   <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_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
+    (<constant>SD_ID128_STRING_MAX</constant>). The ID will be formatted as 32 lowercase hexadecimal digits
+    and be terminated by a <constant>NUL</constant> byte.</para>
+
+    <para><function>SD_ID128_TO_STRING()</function> is a macro that wraps
+    <function>sd_id128_to_string()</function> and passes an appropriately sized buffer as second argument,
+    allocated as C99 compound literal. Each use will thus implicitly acquire a suitable buffer on the stack
+    which remains valid until the end of the current code block. This is usually the simplest way to acquire
+    a string representation of a 128-bit ID in a buffer that is valid in the current code block.</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
-    <constant>NULL</constant> the function will validate the passed ID string, but not actually return it in parsed
-    form.</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 <constant>NULL</constant> the
+    function will validate the passed ID string, but not actually return it in parsed form.</para>
 
     <para>Note that when parsing 37 character UUIDs this is done strictly in Big Endian byte order,
-    i.e. according to <ulink url="https://tools.ietf.org/html/rfc4122">RFC4122</ulink> Variant 1
-    rules, even if the UUID encodes a different variant. This matches behaviour in various other Linux
-    userspace tools. It's probably wise to avoid UUIDs of other variant types.</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
-    <constant>SD_ID128_FORMAT_STR</constant> and <function>SD_ID128_FORMAT_VAL()</function> macros. For
-    more information see
+    i.e. according to <ulink url="https://tools.ietf.org/html/rfc4122">RFC4122</ulink> Variant 1 rules, even
+    if the UUID encodes a different variant. This matches behaviour in various other Linux userspace
+    tools. It's probably wise to avoid UUIDs of other variant types.</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 <constant>SD_ID128_FORMAT_STR</constant> 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>
+    <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>
 
   <xi:include href="libsystemd-pkgconfig.xml" />