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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_message_new_signal"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_message_new_signal</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_message_new_signal</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_message_new_signal</refname>
<refname>sd_bus_message_new_signal_to</refname>
<refpurpose>Create a signal message</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int sd_bus_message_new_signal</funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>const char *<parameter>interface</parameter></paramdef>
<paramdef>const char *<parameter>member</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int sd_bus_message_new_signal_to</funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
<paramdef>const char *<parameter>destination</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>const char *<parameter>interface</parameter></paramdef>
<paramdef>const char *<parameter>member</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>The <function>sd_bus_message_new_signal()</function> function creates a new bus message
object that encapsulates a D-Bus signal, and returns it in the <parameter>m</parameter> output
parameter. The signal will be sent to path <parameter>path</parameter>, on the interface
<parameter>interface</parameter>, member <parameter>member</parameter>. When this message is
sent, no reply is expected. See
<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for a short description of the meaning of the <parameter>path</parameter>,
<parameter>interface</parameter>, and <parameter>member</parameter> parameters.
</para>
<para><function>sd_bus_message_new_signal_to()</function> is a shorthand for creating a new bus message
to a specific destination. It's behavior is similar to calling
<function>sd_bus_message_new_signal()</function> followed by calling
<citerefentry><refentrytitle>sd_bus_message_set_destination</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>This function returns 0 if the message object was successfully created, and a negative
errno-style error code otherwise.</para>
<refsect2>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>The output parameter <parameter>m</parameter> is
<constant>NULL</constant>.</para>
<para>The <parameter>path</parameter> parameter is not a valid D-Bus path
(<literal>/an/object/path</literal>), the <parameter>interface</parameter> parameter is not
a valid D-Bus interface name (<literal>an.interface.name</literal>), or the
<parameter>member</parameter> parameter is not a valid D-Bus member
(<literal>Name</literal>).</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENOTCONN</constant></term>
<listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
the bus is not connected.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENOMEM</constant></term>
<listitem><para>Memory allocation failed.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>Examples</title>
<example>
<title>Send a simple signal</title>
<programlisting><xi:include href="send-unit-files-changed.c" parse="text" /></programlisting>
<para>This function in systemd sources is used to emit the
<literal>UnitFilesChanged</literal> signal when the unit files have been changed.
</para>
</example>
</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_emit_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
<citerefentry><refentrytitle>sd_bus_message_set_destination</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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