<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.defined" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>defined</refname>
  <refpurpose>Checks whether a given named constant exists</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>defined</methodname>
   <methodparam><type>string</type><parameter>constant_name</parameter></methodparam>
  </methodsynopsis>
  <para>
   Checks whether the given constant exists and is defined.
  </para>
  <para>
   This function works also with <link
   linkend="language.oop5.constants">class constants</link> and <link
   linkend="language.types.enumerations">enum cases</link>.
  </para>
  <note>
   <para>
    If you want to see if a variable exists, use <function>isset</function>
    as <function>defined</function> only applies to <link linkend="language.constants">constants</link>. If you want to see if a
    function exists, use <function>function_exists</function>.
   </para>
  </note>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>constant_name</parameter></term>
     <listitem>
      <para>
       The constant name.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &true; if the named constant given by <parameter>constant_name</parameter>
   has been defined, &false; otherwise.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Checking Constants</title>
    <programlisting role="php">
<![CDATA[
<?php

/* Note the use of quotes, this is important. This example is checking
 * if the string 'TEST' is the name of a constant named TEST */
if (defined('TEST')) {
    echo TEST;
}


interface bar {
    const test = 'foobar!';
}

class foo {
    const test = 'foobar!';
}

var_dump(defined('bar::test')); // bool(true)
var_dump(defined('foo::test')); // bool(true)

?>
]]>
    </programlisting>
   </example>
   <example>
    <title>Checking Enum Cases (as of PHP 8.1.0)</title>
    <programlisting role="php">
<![CDATA[
<?php

enum Suit
{
    case Hearts;
    case Diamonds;
    case Clubs;
    case Spades;
}

var_dump(defined('Suit::Hearts')); // bool(true)

?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>define</function></member>
    <member><function>constant</function></member>
    <member><function>get_defined_constants</function></member>
    <member><function>function_exists</function></member>
    <member>The section on <link linkend="language.constants">Constants</link></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
