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man: update sd_bus_message_read_array() docs to clarify return value 0 vs. 1

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(cherry picked from commit 4840807c6ddd15f093eea32acc6bb93ffac67dfe)
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Lennart Poettering 2020-10-14 17:08:26 +02:00 committed by Zbigniew Jędrzejewski-Szmek
parent da2f8dda76
commit b531324cbc
1 changed files with 16 additions and 13 deletions
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29
man/sd_bus_message_read_array.xml
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@ -38,16 +38,16 @@
<refsect1>
<title>Description</title>
<para><function>sd_bus_message_read_array()</function> gives access to an element array in
message <parameter>m</parameter>. The "read pointer" in the message must be right before an
array of type <parameter>type</parameter>. As a special case, <parameter>type</parameter> may be
<constant>NUL</constant>, in which case any type is acceptable. A pointer to the array data is
returned in the parameter <parameter>ptr</parameter> and the size of array data (in bytes) is
returned in the parameter <parameter>size</parameter>. If <parameter>size</parameter> is 0, a
valid non-null pointer will be returned, but it may not be dereferenced. The data is aligned as
appropriate for the data type. The data is part of the message — it may not be modified and is
valid only as long as the message is referenced. After this function returns, the "read pointer"
points at the next element after the array.</para>
<para><function>sd_bus_message_read_array()</function> provides access to an array elements in the
bus message <parameter>m</parameter>. The "read pointer" in the message must be right before an array of type
<parameter>type</parameter>. As a special case, <parameter>type</parameter> may be
<constant>NUL</constant>, in which case any trivial type is acceptable. A pointer to the array data is returned
in the parameter <parameter>ptr</parameter> and the size of array data (in bytes) is returned in the
parameter <parameter>size</parameter>. If the returned <parameter>size</parameter> parameter is 0, a
valid non-null pointer will be returned as <parameter>ptr</parameter>, but it may not be
dereferenced. The data is aligned as appropriate for the data type. The data is part of the message — it
may not be modified and is valid only as long as the message is referenced. After this function returns,
the "read pointer" points at the next element after the array.</para>
<para>Note that this function only supports arrays of trivial types, i.e. arrays of booleans, the various
integer types, as well as floating point numbers. In particular it may not be used for arrays of strings,
@ -58,9 +58,12 @@
<title>Return Value</title>
<para>
On success, <function>sd_bus_message_read_array()</function> returns 0 or
a positive integer. On failure, it returns a negative errno-style error
code.
On success and when an array was read, <function>sd_bus_message_read_array()</function> returns an
integer greater than zero. If invoked while inside a container element (such as an array, e.g. when
operating on an array of arrays) and the final element of the outer container has been read already and
the read pointer is thus behind the last element of the outer container this call returns 0 (and the
returned pointer will be <constant>NULL</constant> and the size will be 0). On failure, it returns a
negative errno-style error code.
</para>
<refsect2>