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

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<!-- splitted from ./en/functions/array.xml, last change in rev 1.2 -->
  <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>int</type><methodname>array_walk</methodname>
      <methodparam><type>array</type><parameter>array</parameter></methodparam>
      <methodparam><type>string</type><parameter>func</parameter></methodparam>
      <methodparam choice="opt"><type>mixed</type><parameter>userdata</parameter></methodparam>
     </methodsynopsis>
    <simpara>
     Applies the user-defined function named by <parameter>func</parameter>
     to each element of <parameter>array</parameter>.
     <parameter>func</parameter> will be passed array value as the
     first parameter and array key as the second parameter.  If
     <parameter>userdata</parameter> is supplied, it will be passed as
     the third parameter to the user function. <parameter>func</parameter>
     must be a user-defined function, and can't be a native PHP function.
     Thus, you can't use <function>array_walk</function> straight with
     <function>str2lower</function>, you must build a user-defined function
     with it first, and pass this function as argument.
    </simpara>
    &note.func-callback;
    <simpara>
     If <parameter>func</parameter> requires more than two or three
     arguments, depending on <parameter>userdata</parameter>, a
     warning will be generated each time
     <function>array_walk</function> calls
     <parameter>func</parameter>. These warnings may be suppressed by
     prepending the '@' sign to the <function>array_walk</function>
     call, or by using <function>error_reporting</function>.
    </simpara>
    <note>
     <para>
      If <parameter>func</parameter> needs to be working with the
      actual values of the array, specify that the first parameter of
      <parameter>func</parameter> should be passed by reference. Then
      any changes made to those elements will be made in the array
      itself.
     </para>
     <para>
      Modifying the array from inside <parameter>func</parameter>
      may cause unpredictable behavior.
     </para>
    </note>
    <note>
     <para>
      Passing the key and userdata to <parameter>func</parameter> was
      added in 4.0.
     </para>
     <para>
      In PHP 4 <function>reset</function> needs to be called as
      necessary since <function>array_walk</function> does not reset
      the array by default.
     </para>
     <para>
      Users may not change the array itself from the callback
      function. e.g. Add/delete element, unset the array that
      <function>array_walk</function> is applied to. If the array is
      changed, the behavior of this function is undefined.
     </para>
    </note>
    <para>
     <example>
      <title><function>array_walk</function> example</title>
      <programlisting role="php">
<![CDATA[
$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');
reset ($fruits);
array_walk ($fruits, 'test_alter', 'fruit');
echo "... and after:\n";
reset ($fruits);
array_walk ($fruits, 'test_print');
]]>
      </programlisting>
      <para>
       The printout of the program above will be:
       <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>
      </para>
     </example>
    </para>
    <simpara>
     See also <function>each</function> and <function>list</function>.
    </simpara>
   </refsect1>
  </refentry>

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