man/sd_bus_slot_set_userdata.xml

   1 <?xml version='1.0'?>
   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+ -->
   5
   6 <refentry id="sd_bus_slot_set_userdata" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_bus_slot_set_userdata</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_bus_slot_set_userdata</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_bus_slot_set_userdata</refname>
  20     <refname>sd_bus_slot_get_userdata</refname>
  21
  22     <refpurpose>Set and query the value in the "userdata" field</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <funcsynopsis>
  27       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  28
  29       <funcprototype>
  30         <funcdef>void* <function>sd_bus_slot_set_userdata</function></funcdef>
  31         <paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef>
  32         <paramdef>void* <parameter>userdata</parameter></paramdef>
  33       </funcprototype>
  34
  35       <funcprototype>
  36         <funcdef>void* <function>sd_bus_slot_get_userdata</function></funcdef>
  37         <paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef>
  38       </funcprototype>
  39
  40     </funcsynopsis>
  41   </refsynopsisdiv>
  42
  43   <refsect1>
  44     <title>Description</title>
  45
  46     <para>The userdata pointer allows data to be passed between the point where a callback is
  47     registered, for example when a filter is added using
  48     <citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  49     or an asynchronous function call is made using
  50     <citerefentry><refentrytitle>sd_bus_call_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  51     and the point where the callback is called, without having any global state. The pointer has
  52     type <type>void*</type> and is not used by the sd-bus functions in any way, except to pass to
  53     the callback function.</para>
  54
  55     <para>Usually, the userdata field is set when the slot object is initially
  56     registered. <function>sd_bus_slot_set_userdata()</function> may be used to change it later for
  57     the bus slot object <parameter>slot</parameter>. Previous value of the field is returned. The
  58     argument and returned value may be <constant>NULL</constant>. It will be passed as the
  59     <parameter>userdata</parameter> argument to the callback function attached to the slot.</para>
  60
  61     <para><function>sd_bus_slot_set_userdata()</function> gets the value of the userdata field in
  62     the bus slot object <parameter>slot</parameter>.</para>
  63   </refsect1>
  64
  65   <refsect1>
  66     <title>Return Value</title>
  67
  68     <para>On success, these functions return the value of the userdata field before the function
  69     call. If the <parameter>slot</parameter> object is <constant>NULL</constant>,
  70     <constant>NULL</constant> will be returned to signify an error, but this is not distinguishable
  71     from the userdata field value being <constant>NULL</constant>.</para>
  72   </refsect1>
  73
  74   <xi:include href="libsystemd-pkgconfig.xml" />
  75
  76   <refsect1>
  77     <title>See Also</title>
  78
  79     <para>
  80       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  81       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  82       <citerefentry><refentrytitle>sd_bus_slot_set_destroy_callback</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  83       <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  84       <citerefentry><refentrytitle>sd_bus_slot_get_current_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  85     </para>
  86   </refsect1>
  87
  88 </refentry>