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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 331477 $ -->
<refentry xmlns="http://docbook.org/ns/docbook" xml: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 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>array_key_exists</methodname>
<methodparam><type>mixed</type><parameter>key</parameter></methodparam>
<methodparam><type>array</type><parameter>array</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.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>key</parameter></term>
<listitem>
<para>
Value to check.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>array</parameter></term>
<listitem>
<para>
An array with keys to check.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
&return.success;
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<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>
<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>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
<note>
<para>
&info.deprecated.alias;
<function>key_exists</function>
</para>
</note>
<note>
<para>
For backward compatibility reasons, <function>array_key_exists</function>
will also return &true; if <parameter>key</parameter> is a property
defined within an <type>object</type> given as
<parameter>array</parameter>. This behaviour should not be relied upon,
and care should be taken to ensure that <parameter>array</parameter> is
an <type>array</type>.
</para>
<para>
To check whether a property exists in an object, use
<function>property_exists</function>.
</para>
</note>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>isset</function></member>
<member><function>array_keys</function></member>
<member><function>in_array</function></member>
<member><function>property_exists</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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