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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_bus_slot_set_userdata" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_slot_set_userdata</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_slot_set_userdata</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_slot_set_userdata</refname>
<refname>sd_bus_slot_get_userdata</refname>
<refpurpose>Set and query the value in the "userdata" field</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>void* <function>sd_bus_slot_set_userdata</function></funcdef>
<paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef>
<paramdef>void* <parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void* <function>sd_bus_slot_get_userdata</function></funcdef>
<paramdef>sd_bus_slot* <parameter>slot</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The userdata pointer allows data to be passed between the point where a callback is
registered, for example when a filter is added using
<citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or an asynchronous function call is made using
<citerefentry><refentrytitle>sd_bus_call_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
and the point where the callback is called, without having any global state. The pointer has
type <type>void*</type> and is not used by the sd-bus functions in any way, except to pass to
the callback function.</para>
<para>Usually, the userdata field is set when the slot object is initially
registered. <function>sd_bus_slot_set_userdata()</function> may be used to change it later for
the bus slot object <parameter>slot</parameter>. Previous value of the field is returned. The
argument and returned value may be <constant>NULL</constant>. It will be passed as the
<parameter>userdata</parameter> argument to the callback function attached to the slot.</para>
<para><function>sd_bus_slot_set_userdata()</function> gets the value of the userdata field in
the bus slot object <parameter>slot</parameter>.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, these functions return the value of the userdata field before the function
call. If the <parameter>slot</parameter> object is <constant>NULL</constant>,
<constant>NULL</constant> will be returned to signify an error, but this is not distinguishable
from the userdata field value being <constant>NULL</constant>.</para>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>History</title>
<para><function>sd_bus_slot_set_userdata()</function> and
<function>sd_bus_slot_get_userdata()</function> were added in version 240.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_set_destroy_callback</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_slot_get_current_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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