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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.define" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>define</refname>
<refpurpose>Defines a named constant</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>define</methodname>
<methodparam><type>string</type><parameter>constant_name</parameter></methodparam>
<methodparam><type>mixed</type><parameter>value</parameter></methodparam>
<methodparam choice="opt"><type>bool</type><parameter>case_insensitive</parameter><initializer>&false;</initializer></methodparam>
</methodsynopsis>
<para>
Defines a named constant at runtime.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>constant_name</parameter></term>
<listitem>
<para>
The name of the constant.
</para>
<note>
<para>
It is possible to <function>define</function> constants with reserved or
even invalid names, whose value can (only) be retrieved with
<function>constant</function>. However, doing so is not recommended.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>value</parameter></term>
<listitem>
<para>
The value of the constant. In PHP 5, <parameter>value</parameter> must
be a <type>scalar</type> value (<type>int</type>,
<type>float</type>, <type>string</type>, <type>bool</type>, or
&null;). In PHP 7, <type>array</type> values are also accepted.
</para>
<warning>
<para>
While it is possible to define <type>resource</type> constants, it is
not recommended and may cause unpredictable behavior.
</para>
</warning>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>case_insensitive</parameter></term>
<listitem>
<para>
If set to &true;, the constant will be defined case-insensitive.
The default behavior is case-sensitive; i.e.
<literal>CONSTANT</literal> and <literal>Constant</literal> represent
different values.
</para>
<warning>
<simpara>
Defining case-insensitive constants is deprecated as of PHP 7.3.0.
As of PHP 8.0.0, only &false; is an acceptable value, passing
&true; will produce a warning.
</simpara>
</warning>
<note>
<para>
Case-insensitive constants are stored as lower-case.
</para>
</note>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
&return.success;
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>8.0.0</entry>
<entry>
Passing &true; to <parameter>case_insensitive</parameter> now emits an <constant>E_WARNING</constant>. Passing &false; is still allowed.
</entry>
</row>
<row>
<entry>7.3.0</entry>
<entry>
<parameter>case_insensitive</parameter> has been deprecated and will be removed in version 8.0.0.
</entry>
</row>
<row>
<entry>7.0.0</entry>
<entry>
<type>array</type> values are allowed.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title>Defining Constants</title>
<programlisting role="php">
<![CDATA[
<?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
define("GREETING", "Hello you.", true);
echo GREETING; // outputs "Hello you."
echo Greeting; // outputs "Hello you."
// Works as of PHP 7
define('ANIMALS', array(
'dog',
'cat',
'bird'
));
echo ANIMALS[1]; // outputs "cat"
?>
]]>
</programlisting>
</example>
</para>
<para>
<example>
<title>Constants with Reserved Names</title>
<para>
This example illustrates the <emphasis>possibility</emphasis> to define a
constant with the same name as a
<link linkend="language.constants.predefined">magic constant</link>.
Since the resulting behavior is obviously confusing, it is not recommended
to do this in practise, though.
</para>
<programlisting role="php">
<![CDATA[
<?php
var_dump(defined('__LINE__'));
var_dump(define('__LINE__', 'test'));
var_dump(constant('__LINE__'));
var_dump(__LINE__);
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
bool(false)
bool(true)
string(4) "test"
int(5)
]]>
</screen>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>defined</function></member>
<member><function>constant</function></member>
<member>The section on <link linkend="language.constants">Constants</link></member>
</simplelist>
</para>
</refsect1>
</refentry>
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