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fe45f8dc9b
In the troff output, this doesn't seem to make any difference. But in the html output, the whitespace is sometimes preserved, creating an additional gap before the following content. Drop it everywhere to avoid this.
240 lines
9.6 KiB
XML
240 lines
9.6 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/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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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 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 appends a sequence of fields to
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the D-Bus message object <parameter>m</parameter>. The type string <parameter>types</parameter>
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describes the types of the field arguments that follow. For each type specified in the type
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string, one or more arguments need to be specified, in the same order as declared in the type
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string.</para>
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<para>The type string is composed of the elements shown in the table below. It contains zero or
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more single "complete types". 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 the contained types, a
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variant, an array with its element type, or a dictionary entry with the contained types. The
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type string is <constant>NUL</constant>-terminated.</para>
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<para>In case of a basic type, one argument of the corresponding type is expected.</para>
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<para>A structure is denoted by a sequence of complete types between <literal>(</literal> and
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<literal>)</literal>. This sequence cannot be empty — it must contain at least one type.
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Arguments corresponding to this nested sequence follow the same rules as if they were not
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nested.</para>
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<para>A variant is denoted by <literal>v</literal>. Corresponding arguments must begin with a
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type string denoting a complete type, and following that, arguments corresponding to the
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specified type.</para>
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<para>An array is denoted by <literal>a</literal> followed by a complete type. Corresponding
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arguments must begin with the number of entries in the array, followed by the entries
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themselves, matching the element type of the array.</para>
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<para>A dictionary is an array of dictionary entries, denoted by <literal>a</literal> followed
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by a pair of complete types between <literal>{</literal> and <literal>}</literal>. The first of
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those types must be a basic type. Corresponding arguments must begin with the number of
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dictionary entries, followed by a pair of values for each entry matching the element type of the
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dictionary entries.</para>
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<para><function>sd_bus_message_appendv()</function> is equivalent to
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<function>sd_bus_message_append()</function>, except that it is called with a
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<literal>va_list</literal> instead of a variable number of arguments. This function does not
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call the <function>va_end()</function> macro. Because it invokes the
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<function>va_arg()</function> macro, the value of <parameter>ap</parameter> is undefined after
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the call.</para>
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<para>For further details on the D-Bus type system, please consult the
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<ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html#type-system">D-Bus Specification</ulink>.
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</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 <literal>s</literal> and <literal>g</literal> (unicode string or signature), the pointer
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may be <constant>NULL</constant>, which is equivalent to an empty string. For <literal>h</literal> (UNIX
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file descriptor), the descriptor is duplicated by this call and the passed descriptor stays in possession
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of the caller. 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 a non-negative integer. On failure, they return a
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negative 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><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_bus_message_open_container</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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