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<?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 constant with the given name 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 a constant with the given <parameter>constant_name</parameter>
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>
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