<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.11 $ -->
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  <refentry id="function.array-key-exists">
   <refnamediv>
    <refname>array_key_exists</refname>
    <refpurpose>Checks if the given key or index exists in the array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>bool</type><methodname>array_key_exists</methodname>
      <methodparam><type>mixed</type><parameter>key</parameter></methodparam>
      <methodparam><type>array</type><parameter>search</parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>array_key_exists</function> returns &true; if the
     given <parameter>key</parameter> is set in the array.
     <parameter>key</parameter> can be any value possible
     for an array index. <function>array_key_exists</function> also works
     on objects.
    </para>
    <para>
     <example>
      <title><function>array_key_exists</function> example</title>
      <programlisting role="php">
<![CDATA[
<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>
]]>
      </programlisting>
     </example>
    </para>
    <note>
     <simpara>
      The name of this function is <function>key_exists</function>
      in PHP 4.0.6.
     </simpara>
    </note>
    <example>
     <title><function>array_key_exists</function> vs <function>isset</function></title>
     <para>
      <function>isset</function> does not return &true; for array keys
      that correspond to a &null; value, while
      <function>array_key_exists</function> does.
     </para>
      <programlisting role="php">
<![CDATA[
<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>
]]>
      </programlisting>
    </example>
    <para>
     See also <function>isset</function>, 
     <function>array_keys</function>, and
     <function>in_array</function>.
    </para>
   </refsect1>
  </refentry>

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