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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+
Copyright © 2016 Julian Orth
-->
<refentry id="sd_bus_message_read_basic">
<refentryinfo>
<title>sd_bus_message_read_basic</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_message_read_basic</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_message_read_basic</refname>
<refpurpose>Read a basic type from a message</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_bus_message_read_basic</function></funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>char <parameter>type</parameter></paramdef>
<paramdef>void *<parameter>p</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<function>sd_bus_message_read_basic()</function> reads a basic type from a
message and advances the read position in the message. The set of basic
types and their ascii codes passed in <parameter>type</parameter> are
described in the <ulink
url="https://dbus.freedesktop.org/doc/dbus-specification.html">D-Bus
Specification</ulink>.
</para>
<para>
If <parameter>p</parameter> is not <constant>NULL</constant>, it should contain
a pointer to an appropriate object. For example, if <parameter>type</parameter>
is <constant>'y'</constant>, the object passed in <parameter>p</parameter>
should have type <type>uint8_t *</type>. If <parameter>type</parameter> is
<constant>'s'</constant>, the object passed in <parameter>p</parameter> should
have type <type>const char **</type>. Note that, if the basic type is a pointer
(e.g., <type>const char *</type> in the case of a string), the pointer is only
borrowed and the contents must be copied if they are to be used after the end
of the messages lifetime. Similarly, during the lifetime of such a pointer, the
message must not be modified. See the table below for a complete list of allowed
types.
</para>
<table id='format-specifiers'>
<title>Item type specifiers</title>
<tgroup cols='4'>
<colspec colname='specifier' />
<colspec colname='constant' />
<colspec colname='description' />
<colspec colname='ctype' />
<thead>
<row>
<entry>Specifier</entry>
<entry>Constant</entry>
<entry>Description</entry>
<entry>Expected C Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>y</literal></entry>
<entry><constant>SD_BUS_TYPE_BYTE</constant></entry>
<entry>8bit unsigned integer</entry>
<entry><type>uint8_t *</type></entry>
</row>
<row>
<entry><literal>b</literal></entry>
<entry><constant>SD_BUS_TYPE_BOOLEAN</constant></entry>
<entry>boolean</entry>
<entry><type>int *</type> (NB: not <type>bool *</type>)</entry>
</row>
<row>
<entry><literal>n</literal></entry>
<entry><constant>SD_BUS_TYPE_INT16</constant></entry>
<entry>16bit signed integer</entry>
<entry><type>int16_t *</type></entry>
</row>
<row>
<entry><literal>q</literal></entry>
<entry><constant>SD_BUS_TYPE_UINT16</constant></entry>
<entry>16bit unsigned integer</entry>
<entry><type>uint16_t *</type></entry>
</row>
<row>
<entry><literal>i</literal></entry>
<entry><constant>SD_BUS_TYPE_INT32</constant></entry>
<entry>32bit signed integer</entry>
<entry><type>int32_t *</type></entry>
</row>
<row>
<entry><literal>u</literal></entry>
<entry><constant>SD_BUS_TYPE_UINT32</constant></entry>
<entry>32bit unsigned integer</entry>
<entry><type>uint32_t *</type></entry>
</row>
<row>
<entry><literal>x</literal></entry>
<entry><constant>SD_BUS_TYPE_INT64</constant></entry>
<entry>64bit signed integer</entry>
<entry><type>int64_t *</type></entry>
</row>
<row>
<entry><literal>t</literal></entry>
<entry><constant>SD_BUS_TYPE_UINT64</constant></entry>
<entry>64bit unsigned integer</entry>
<entry><type>uint64_t *</type></entry>
</row>
<row>
<entry><literal>d</literal></entry>
<entry><constant>SD_BUS_TYPE_DOUBLE</constant></entry>
<entry>IEEE 754 double precision floating-point</entry>
<entry><type>double *</type></entry>
</row>
<row>
<entry><literal>s</literal></entry>
<entry><constant>SD_BUS_TYPE_STRING</constant></entry>
<entry>UTF-8 string</entry>
<entry><type>const char **</type></entry>
</row>
<row>
<entry><literal>o</literal></entry>
<entry><constant>SD_BUS_TYPE_OBJECT_PATH</constant></entry>
<entry>D-Bus object path string</entry>
<entry><type>const char **</type></entry>
</row>
<row>
<entry><literal>g</literal></entry>
<entry><constant>SD_BUS_TYPE_SIGNATURE</constant></entry>
<entry>D-Bus signature string</entry>
<entry><type>const char **</type></entry>
</row>
<row>
<entry><literal>h</literal></entry>
<entry><constant>SD_BUS_TYPE_UNIX_FD</constant></entry>
<entry>UNIX file descriptor</entry>
<entry><type>int *</type></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
If there is no object of the specified type at the current position in the
message, an error is returned.
</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>
On success, <function>sd_bus_message_read_basic()</function> returns 0 or
a positive integer. On failure, it returns a negative errno-style error
code.
</para>
<refsect2 id='errors'>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>Specified type string is invalid or the message parameter is
<constant>NULL</constant>.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENXIO</constant></term>
<listitem><para>The message does not contain the specified type at current position.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-EBADMSG</constant></term>
<listitem><para>The message cannot be parsed.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
</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_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_skip</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_message_read</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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