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<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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