array-key-exists.xml

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<refentry xml:id="function.array-key-exists" xmlns="http://docbook.org/ns/docbook">
 <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 class="union"><type>string</type><type>int</type><type>float</type><type>bool</type><type>resource</type><type>null</type></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>
  <note>
   <para>
    <function>array_key_exists</function> will search for the keys in the first dimension only.
    Nested keys in multidimensional arrays will not be found.
   </para>
  </note>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <informaltable>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>&Version;</entry>
      <entry>&Description;</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry>8.0.0</entry>
      <entry>
       The <parameter>key</parameter> parameter now accepts
       <parameter>bool</parameter>, <parameter>float</parameter>, <parameter>int</parameter>,
       <parameter>null</parameter>, <parameter>resource</parameter>, and
       <parameter>string</parameter> as arguments.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </informaltable>
 </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>
     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 is deprecated as of PHP 7.4.0,
     and removed as of PHP 8.0.0.
    </para>
    <para>
     To check whether a property exists in an object,
     <function>property_exists</function> should be used.
    </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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