php-doc-en/reference/array/functions/array-walk.xml

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<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>callback</type><parameter>funcname</parameter></methodparam>
   <methodparam choice="opt"><type>mixed</type><parameter>userdata</parameter></methodparam>
  </methodsynopsis>
  <simpara>
   Applies the user-defined function <parameter>funcname</parameter> 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>funcname</parameter></term>
     <listitem>
      <para>
       Typically, <parameter>funcname</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>funcname</parameter> needs to be working with the
        actual values of the array, specify the first parameter of
        <parameter>funcname</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>
      <para>
       Users may not change the <parameter>array</parameter> itself from the
       callback function. e.g. Add/delete elements, unset elements, etc.  If
       the array that <function>array_walk</function> is applied to is
       changed, 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 callback
       <parameter>funcname</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>funcname</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>funcname</parameter>. These warnings may be suppressed by
   prepending the PHP error operator
   <link linkend="language.operators.errorcontrol">@</link> to the
   <function>array_walk</function> call, or by using
   <function>error_reporting</function>.
  </para>
 </refsect1>
 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>4.0.0</entry>
       <entry>
        Passing the key and <parameter>userdata</parameter> to
        <parameter>funcname</parameter> was added.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </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>create_function</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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