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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 331556 $ -->
<refentry xml:id="function.array-walk" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>array_walk</refname>
<refpurpose>Apply a user function to every member of an array</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>array_walk</methodname>
<methodparam><type>array</type><parameter role="reference">array</parameter></methodparam>
<methodparam><type>callable</type><parameter>callback</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>userdata</parameter><initializer>&null;</initializer></methodparam>
</methodsynopsis>
<simpara>
Applies the user-defined <parameter>callback</parameter> function to each
element of the <parameter>array</parameter> array.
</simpara>
<para>
<function>array_walk</function> is not affected by the internal array
pointer of <parameter>array</parameter>. <function>array_walk</function>
will walk through the entire array regardless of pointer position.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>array</parameter></term>
<listitem>
<para>
The input array.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>callback</parameter></term>
<listitem>
<para>
Typically, <parameter>callback</parameter> takes on two parameters.
The <parameter>array</parameter> parameter's value being the first, and
the key/index second.
</para>
<note>
<para>
If <parameter>callback</parameter> needs to be working with the
actual values of the array, specify the first parameter of
<parameter>callback</parameter> as a
<link linkend="language.references">reference</link>. Then,
any changes made to those elements will be made in the
original array itself.
</para>
</note>
<note>
<para>
Many internal functions (for example <function>strtolower</function>)
will throw a warning if more than the expected number of argument
are passed in and are not usable directly as a
<parameter>callback</parameter>.
</para>
</note>
<para>
Only the values of the <parameter>array</parameter> may potentially be
changed; its structure cannot be altered, i.e., the programmer cannot
add, unset or reorder elements. If the callback does not respect this
requirement, the behavior of this function is undefined, and
unpredictable.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>userdata</parameter></term>
<listitem>
<para>
If the optional <parameter>userdata</parameter> parameter is supplied,
it will be passed as the third parameter to the
<parameter>callback</parameter>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
&return.success;
</para>
</refsect1>
<refsect1 role="errors">
&reftitle.errors;
<para>
If function <parameter>callback</parameter> requires more parameters than
given to it, an error of level <link linkend="errorfunc.constants">
E_WARNING</link> will be generated each time <function>array_walk</function>
calls <parameter>callback</parameter>.
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>array_walk</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");
function test_alter(&$item1, $key, $prefix)
{
$item1 = "$prefix: $item1";
}
function test_print($item2, $key)
{
echo "$key. $item2<br />\n";
}
echo "Before ...:\n";
array_walk($fruits, 'test_print');
array_walk($fruits, 'test_alter', 'fruit');
echo "... and after:\n";
array_walk($fruits, 'test_print');
?>
]]>
</programlisting>
&example.outputs;
<screen role="php">
<![CDATA[
Before ...:
d. lemon
a. orange
b. banana
c. apple
... and after:
d. fruit: lemon
a. fruit: orange
b. fruit: banana
c. fruit: apple
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>array_walk_recursive</function></member>
<member><function>iterator_apply</function></member>
<member><function>list</function></member>
<member><function>each</function></member>
<member><function>call_user_func_array</function></member>
<member><function>array_map</function></member>
<member>&seealso.callback;</member>
<member>&foreach;</member>
</simplelist>
</para>
</refsect1>
</refentry>
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