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| <!-- |
| SPDX-License-Identifier: LGPL-2.1-or-later |
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| 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. If <parameter>type</parameter> is |
| <constant>'h'</constant> (UNIX file descriptor), the descriptor is not duplicated by this call and the |
| returned descriptor remains in possession of the message object, and needs to be duplicated by the caller |
| in order to keep an open reference to it after the message object is freed (for example by calling |
| <literal>fcntl(fd, FD_DUPFD_CLOEXEC, 3)</literal>). 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> |