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<refentry id="sd_bus_message_append"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_message_append</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_message_append</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_message_append</refname>
<refname>sd_bus_message_appendv</refname>
<refpurpose>Attach fields to a D-Bus message based on a type
string</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-bus.h></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>
<funcprototype>
<funcdef>int sd_bus_message_appendv</funcdef>
<paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
<paramdef>const char *<parameter>types</parameter></paramdef>
<paramdef>va_list <parameter>ap</parameter></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>The <function>sd_bus_message_appendv()</function> is equivalent to
the function <function>sd_bus_message_append()</function>,
except that it is called with a <literal>va_list</literal> instead of
a variable number of arguments. This function does not call the
<function>va_end()</function> macro. Because it invokes the
<function>va_arg()</function> macro, the value of ap
is undefined after the call.</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>
<para>For types "s" and "g" (unicode string or signature), the pointer may be
<constant>NULL</constant>, which is equivalent to an empty string. See
<citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for the precise interpretation of those and other types.</para>
</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, these functions return 0 or a positive
integer. On failure, these functions return a negative
errno-style error code.</para>
</refsect1>
<xi:include href="sd_bus_message_append_basic.xml" xpointer="errors" />
<xi:include href="libsystemd-pkgconfig.xml" />
<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>