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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
250 lines
9.3 KiB
XML
250 lines
9.3 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_bus_message_append"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_message_append</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_message_append</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_message_append</refname>
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<refname>sd_bus_message_appendv</refname>
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<refpurpose>Attach fields to a D-Bus message based on a type
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string</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int sd_bus_message_append</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>const char *<parameter>types</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int sd_bus_message_appendv</funcdef>
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<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
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<paramdef>const char *<parameter>types</parameter></paramdef>
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<paramdef>va_list <parameter>ap</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The <function>sd_bus_message_append()</function> function
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appends a sequence of fields to the D-Bus message object
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<parameter>m</parameter>. The type string
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<parameter>types</parameter> describes the types of the field
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arguments that follow. For each type specified in the type string,
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one or more arguments need to be specified, in the same order as
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declared in the type string.</para>
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<para>The type string is composed of the elements shown in the
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table below. It contains zero or more single "complete types".
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Each complete type may be one of the basic types or a fully
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described container type. A container type may be a structure with
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the contained types, a variant, an array with its element type, or
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a dictionary entry with the contained types. The type string is
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<constant>NUL</constant>-terminated.</para>
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<para>In case of a basic type, one argument of the corresponding
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type is expected.</para>
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<para>A structure is denoted by a sequence of complete types
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between <literal>(</literal> and <literal>)</literal>. This
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sequence cannot be empty — it must contain at least one type.
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Arguments corresponding to this nested sequence follow the same
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rules as if they were not nested.</para>
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<para>A variant is denoted by <literal>v</literal>. Corresponding
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arguments must begin with a type string denoting a complete type,
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and following that, arguments corresponding to the specified type.
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</para>
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<para>An array is denoted by <literal>a</literal> followed by a
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complete type. Corresponding arguments must begin with the number of
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entries in the array, followed by the entries themselves,
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matching the element type of the array.</para>
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<para>A dictionary is an array of dictionary entries, denoted by
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<literal>a</literal> followed by a pair of complete types between
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<literal>{</literal> and <literal>}</literal>. The first of those
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types must be a basic type. Corresponding arguments must begin
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with the number of dictionary entries, followed by a pair of
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values for each entry matching the element type of
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the dictionary entries.</para>
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<para>The <function>sd_bus_message_appendv()</function> is equivalent to the
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<function>sd_bus_message_append()</function>, except that it is called with
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a <literal>va_list</literal> instead of a variable number of arguments. This
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function does not call the <function>va_end()</function> macro. Because it
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invokes the <function>va_arg()</function> macro, the value of
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<parameter>ap</parameter> is undefined after the call.</para>
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<para>For further details on the D-Bus type system, please consult
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the <ulink
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url="http://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus
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Specification</ulink>.</para>
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<table>
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<title>Item type specifiers</title>
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<tgroup cols='5'>
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<xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers'])//colspec" />
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<xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//thead)" />
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<tbody>
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<xi:include href="sd_bus_message_append_basic.xml" xpointer="xpointer(//table[@id='format-specifiers']//tbody/*)" />
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<row>
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<entry><literal>a</literal></entry>
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<entry><constant>SD_BUS_TYPE_ARRAY</constant></entry>
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<entry>array</entry>
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<entry>determined by array type and size</entry>
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<entry>int, followed by array contents</entry>
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</row>
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<row>
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<entry><literal>v</literal></entry>
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<entry><constant>SD_BUS_TYPE_VARIANT</constant></entry>
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<entry>variant</entry>
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<entry>determined by the type argument</entry>
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<entry>signature string, followed by variant contents</entry>
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</row>
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<row>
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<entry><literal>(</literal></entry>
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<entry><constant>SD_BUS_TYPE_STRUCT_BEGIN</constant></entry>
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<entry>array start</entry>
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<entry morerows="1">determined by the nested types</entry>
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<entry morerows="1">structure contents</entry>
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</row>
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<row>
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<entry><literal>)</literal></entry>
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<entry><constant>SD_BUS_TYPE_STRUCT_END</constant></entry>
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<entry>array end</entry>
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</row>
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<row>
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<entry><literal>{</literal></entry>
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<entry><constant>SD_BUS_TYPE_DICT_ENTRY_BEGIN</constant></entry>
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<entry>dictionary entry start</entry>
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<entry morerows="1">determined by the nested types</entry>
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<entry morerows="1">dictionary contents</entry>
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</row>
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<row>
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<entry><literal>}</literal></entry>
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<entry><constant>SD_BUS_TYPE_DICT_ENTRY_END</constant></entry>
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<entry>dictionary entry end</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>For types "s" and "g" (unicode string or signature), the pointer may be
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<constant>NULL</constant>, which is equivalent to an empty string. See
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<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for the precise interpretation of those and other types.</para>
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</refsect1>
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<refsect1>
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<title>Types String Grammar</title>
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<programlisting>types ::= complete_type*
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complete_type ::= basic_type | variant | structure | array | dictionary
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basic_type ::= "y" | "n" | "q" | "u" | "i" | "x" | "t" | "d" |
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"b" | "h" |
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"s" | "o" | "g"
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variant ::= "v"
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structure ::= "(" complete_type+ ")"
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array ::= "a" complete_type
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dictionary ::= "a" "{" basic_type complete_type "}"
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</programlisting>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>Append a single basic type (the string <literal>a string</literal>):
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</para>
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<programlisting>sd_bus_message *m;
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…
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sd_bus_message_append(m, "s", "a string");</programlisting>
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<para>Append all types of integers:</para>
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<programlisting>uint8_t y = 1;
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int16_t n = 2;
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uint16_t q = 3;
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int32_t i = 4;
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uint32_t u = 5;
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int32_t x = 6;
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uint32_t t = 7;
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double d = 8.0;
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sd_bus_message_append(m, "ynqiuxtd", y, n, q, i, u, x, t, d);</programlisting>
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<para>Append a structure composed of a string and a D-Bus path:</para>
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<programlisting>sd_bus_message_append(m, "(so)", "a string", "/a/path");
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</programlisting>
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<para>Append an array of UNIX file descriptors:</para>
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<programlisting>sd_bus_message_append(m, "ah", 3, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO);
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</programlisting>
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<para>Append a variant, with the real type "g" (signature),
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and value "sdbusisgood":</para>
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<programlisting>sd_bus_message_append(m, "v", "g", "sdbusisgood");</programlisting>
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<para>Append a dictionary containing the mapping {1=>"a", 2=>"b", 3=>""}:
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</para>
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<programlisting>sd_bus_message_append(m, "a{is}", 3, 1, "a", 2, "b", 3, NULL);
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</programlisting>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive integer. On failure, they return a negative
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errno-style error code.</para>
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<xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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