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<refentry id="sd_bus_new">

<refentryinfo>

<title>sd_bus_new</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>A monkey with a typewriter</contrib>

<firstname>Zbigniew</firstname>

<surname>Jędrzejewski-Szmek</surname>

<email>zbyszek@in.waw.pl</email>

</author>

</authorgroup>

</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 &lt;systemd/sd-bus.h&gt;</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>bus</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(&amp;bus);

if (r &lt; 0)

fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));

…

}</programlisting>

<para><function>sd_bus_ref()</function>,

<function>sd_bus_unref()</function> and

<function>sd_bus_unrefp()</function> execute no operation if the

passed in bus object 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>

<refsect1>

<title>Notes</title>

<para><function>sd_bus_new()</function> and other functions

described here are available as a shared library, which can be

compiled and linked to with the

<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

file.</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_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>