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

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  <refentry id="function.array-walk">
   <refnamediv>
    <refname>array_walk</refname>
    <refpurpose>
     Apply a user function to every member of an array
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <methodsynopsis>
     <type>bool</type><methodname>array_walk</methodname>
     <methodparam><type>array</type><parameter>&amp;array</parameter></methodparam>
     <methodparam><type>callback</type><parameter>funcname</parameter></methodparam>
     <methodparam choice="opt"><type>mixed</type><parameter>userdata</parameter></methodparam>
    </methodsynopsis>
    <simpara>
     &return.success;
    </simpara>
    <simpara>
     Applies the user-defined function <parameter>funcname</parameter> to each
     element of the <parameter>array</parameter> array. Typically, 
     <parameter>funcname</parameter> takes on two parameters.
     The <parameter>array</parameter> parameter's value being the first, and
     the key/index second. If the optional <parameter>userdata</parameter>
     parameter is supplied, it will be passed as the third parameter to
     the callback <parameter>funcname</parameter>.
    </simpara>
    <simpara>
     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>.
    </simpara>
    <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>
    <note>
     <para>
      Passing the key and userdata to <parameter>funcname</parameter> was
      added in 4.0.0
     </para>
    </note>
    <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.  To reset the pointer, use 
     <function>reset</function>.  In PHP 3, 
     <function>array_walk</function> resets the pointer.
    </para>
    <para>
     Users may not change the array 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>
    <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>
      <para>
       The printout of the program above will be:
      </para>
      <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>
    <simpara>
     See also <function>array_walk_recursive</function>,
     <function>create_function</function>,
     <function>list</function>,
     <link linkend="control-structures.foreach">foreach</link>, 
     <function>each</function>,
     <function>call_user_func_array</function>, and
     <function>array_map</function>.
    </simpara>
   </refsect1>
  </refentry>

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