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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_bus_message_append"

xmlns:xi="http://www.w3.org/2001/XInclude">

<refentryinfo>

<title>sd_bus_message_append</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_message_append</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_bus_message_append</refname>

<refpurpose>Attach fields to a D-Bus message based on a type

string</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>

<funcprototype>

<funcdef>int sd_bus_message_append</funcdef>

<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>

<paramdef>const char *<parameter>types</parameter></paramdef>

<paramdef>...</paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para>The <function>sd_bus_message_append()</function> function

appends a sequence of fields to the D-Bus message object

<parameter>m</parameter>. The type string

<parameter>types</parameter> describes the types of the field

arguments that follow. For each type specified in the type string,

one or more arguments need to be specified, in the same order as

declared in the type string.</para>

<para>The type string is composed of the elements shown in the

table below. It contains zero or more single "complete types".

Each complete type may be one of the basic types or a fully

described container type. A container type may be a structure with

the contained types, a variant, an array with its element type, or

a dictionary entry with the contained types. The type string is

<constant>NUL</constant>-terminated.</para>

<para>In case of a basic type, one argument of the corresponding

type is expected.</para>

<para>A structure is denoted by a sequence of complete types

between <literal>(</literal> and <literal>)</literal>. This

sequence cannot be empty — it must contain at least one type.

Arguments corresponding to this nested sequence follow the same

rules as if they were not nested.</para>

<para>A variant is denoted by <literal>v</literal>. Corresponding

arguments must begin with a type string denoting a complete type,

and following that, arguments corresponding to the specified type.

</para>

<para>An array is denoted by <literal>a</literal> followed by a

complete type. Corresponding arguments must begin with the number of

entries in the array, followed by the entries themselves,

matching the element type of the array.</para>

<para>A dictionary is an array of dictionary entries, denoted by

<literal>a</literal> followed by a pair of complete types between

<literal>{</literal> and <literal>}</literal>. The first of those

types must be a basic type. Corresponding arguments must begin

with the number of dictionary entries, followed by a pair of

values for each entry matching the element type of

the dictionary entries.</para>

<para>For further details on the D-Bus type system, please consult

the <ulink

url="http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus

Specification</ulink>.</para>

<table>

<title>Item type specifiers</title>

<tgroup cols='5'>

<xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />

<xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />

<tbody>

<xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />

<row>

<entry><literal>a</literal></entry>

<entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>

<entry>array</entry>

<entry>determined by array type and size</entry>

<entry>int, followed by array contents</entry>

</row>

<row>

<entry><literal>v</literal></entry>

<entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>

<entry>variant</entry>

<entry>determined by the type argument</entry>

<entry>signature string, followed by variant contents</entry>

</row>

<row>

<entry><literal>(</literal></entry>

<entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>

<entry>array start</entry>

<entry morerows="1">determined by the nested types</entry>

<entry morerows="1">structure contents</entry>

</row>

<row>

<entry><literal>)</literal></entry>

<entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>

<entry>array end</entry>

</row>

<row>

<entry><literal>{</literal></entry>

<entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>

<entry>dictionary entry start</entry>

<entry morerows="1">determined by the nested types</entry>

<entry morerows="1">dictionary contents</entry>

</row>

<row>

<entry><literal>}</literal></entry>

<entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>

<entry>dictionary entry end</entry>

</row>

</tbody>

</tgroup>

</table>

</refsect1>

<refsect1>

<title>Types String Grammar</title>

<programlisting>types ::= complete_type*

complete_type ::= basic_type | variant | structure | array | dictionary

basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |

"b" | "h" |

"s" | "o" | "g"

variant ::= "v"

structure ::= "(" complete_type+ ")"

array ::= "a" complete_type

dictionary ::= "a" "{" basic_type complete_type "}"

</programlisting>

</refsect1>

<refsect1>

<title>Examples</title>

<para>Append a single basic type (the string <literal>a string</literal>):

</para>

<programlisting>sd_bus_message *m;

...

sd_bus_message_append(m, "s", "a string");</programlisting>

<para>Append all types of integers:</para>

<programlisting>uint8_t y = 1;

int16_t n = 2;

uint16_t q = 3;

int32_t i = 4;

uint32_t u = 5;

int32_t x = 6;

uint32_t t = 7;

double d = 8.0;

sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>

<para>Append a structure composed of a string and a D-Bus path:</para>

<programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");

</programlisting>

<para>Append an array of UNIX file descriptors:</para>

<programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);

</programlisting>

<para>Append a variant, with the real type "g" (signature),

and value "sdbusisgood":</para>

<programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>

<para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:

</para>

<programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);

</programlisting>

</refsect1>

<refsect1>

<title>Return Value</title>

<para>On success, this call returns 0 or a positive

integer. On failure, this call returns a negative

errno-style error code.</para>

</refsect1>

<xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />

<refsect1>

<title>Notes</title>

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

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

compiled and linked to with the

<constant>libsystemd-bus</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_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>