php-doc-en/reference/array/functions/array-key-exists.xml

<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.12 $ -->
<!-- splitted from ./en/functions/array.xml, last change in rev 1.119 -->
<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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