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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="sd_bus_new" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_new</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_new</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_new</refname>
<refname>sd_bus_ref</refname>
<refname>sd_bus_unref</refname>
<refname>sd_bus_unrefp</refname>
<refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_new</function></funcdef>
<paramdef>sd_bus **<parameter>bus</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>sd_bus *<function>sd_bus_ref</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sd_bus_unrefp</function></funcdef>
<paramdef>sd_bus **<parameter>busp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_bus_new()</function> creates a new bus
object. This object is reference-counted, and will be destroyed
when all references are gone. Initially, the caller of this
function owns the sole reference and the bus object will not be
connected to any bus. To connect it to a bus, make sure
to set an address with
<citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or a related call, and then start the connection with
<citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>In most cases, it is a better idea to invoke
<citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or related calls instead of the more low-level
<function>sd_bus_new()</function> and
<function>sd_bus_start()</function>. The higher-level calls not
only allocate a bus object but also start the connection to a
well-known bus in a single function invocation.</para>
<para><function>sd_bus_ref()</function> increases the reference
counter of <parameter>bus</parameter> by one.</para>
<para><function>sd_bus_unref()</function> decreases the reference
counter of <parameter>bus</parameter> by one. Once the reference
count has dropped to zero, <parameter>bus</parameter> is destroyed
and cannot be used anymore, so further calls to
<function>sd_bus_ref()</function> or
<function>sd_bus_unref()</function> are illegal.</para>
<para><function>sd_bus_unrefp()</function> is similar to
<function>sd_bus_unref()</function> but takes a pointer to a
pointer to an <type>sd_bus</type> object. This call is useful in
conjunction with GCC's and LLVM's <ulink
url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
Variable Attribute</ulink>. Note that this function is defined as
inline function. Use a declaration like the following, in order to
allocate a bus object that is freed automatically as the code
block is left:</para>
<programlisting>{
__attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
int r;
…
r = sd_bus_default(&bus);
if (r < 0)
fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
…
}</programlisting>
<para><function>sd_bus_ref()</function> and <function>sd_bus_unref()</function>
execute no operation if the passed in bus object address is
<constant>NULL</constant>. <function>sd_bus_unrefp()</function> will first
dereference its argument, which must not be <constant>NULL</constant>, and will
execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, <function>sd_bus_new()</function> returns 0 or a
positive integer. On failure, it returns a negative errno-style
error code.</para>
<para><function>sd_bus_ref()</function> always returns the argument.
</para>
<para><function>sd_bus_unref()</function> always returns
<constant>NULL</constant>.</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-ENOMEM</constant></term>
<listitem><para>Memory allocation failed.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<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_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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