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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.constant" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>constant</refname>
<refpurpose>Returns the value of a constant</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>mixed</type><methodname>constant</methodname>
<methodparam><type>string</type><parameter>name</parameter></methodparam>
</methodsynopsis>
<simpara>
Return the value of the constant indicated by
<parameter>name</parameter>.
</simpara>
<simpara>
<function>constant</function> is useful if you need to retrieve
the value of a constant, but do not know its name. I.e. it is
stored in a variable or returned by a function.
</simpara>
<simpara>
This function works also with <link
linkend="language.oop5.constants">class constants</link> and <link
linkend="language.types.enumerations">enum cases</link>.
</simpara>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>name</parameter></term>
<listitem>
<para>
The constant name.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns the value of the constant.
</para>
</refsect1>
<refsect1 role="errors">
&reftitle.errors;
<para>
If the constant is not defined, an <classname>Error</classname> exception is thrown.
Prior to PHP 8.0.0, an <constant>E_WARNING</constant> level error was generated in that case.
</para>
</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>
If the constant is not defined, <function>constant</function> now throws an
<classname>Error</classname> exception; previously an <constant>E_WARNING</constant>
was generated, and &null; was returned.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title>Using <function>constant</function> with Constants</title>
<programlisting role="php">
<![CDATA[
<?php
define("MAXSIZE", 100);
echo MAXSIZE;
echo constant("MAXSIZE"); // same thing as the previous line
interface bar {
const test = 'foobar!';
}
class foo {
const test = 'foobar!';
}
$const = 'test';
var_dump(constant('bar::'. $const)); // string(7) "foobar!"
var_dump(constant('foo::'. $const)); // string(7) "foobar!"
?>
]]>
</programlisting>
</example>
<example>
<title>Using <function>constant</function> with Enum Cases (as of PHP 8.1.0)</title>
<programlisting role="php">
<![CDATA[
<?php
enum Suit
{
case Hearts;
case Diamonds;
case Clubs;
case Spades;
}
$case = 'Hearts';
var_dump(constant('Suit::'. $case)); // enum(Suit::Hearts)
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>define</function></member>
<member><function>defined</function></member>
<member><function>get_defined_constants</function></member>
<member>The section on <link linkend="language.constants">Constants</link></member>
</simplelist>
</para>
</refsect1>
</refentry>
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