reference/misc/functions/defined.xml
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36e1d917ef7be36e8b4ff5193b456390061f2e21
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<refentry xml:id="function.defined" xmlns="http://docbook.org/ns/docbook">
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<refnamediv>
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<refname>defined</refname>
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<refpurpose>Checks whether a given named constant exists</refpurpose>
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<refpurpose>Checks whether a constant with the given name exists</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>bool</type><methodname>defined</methodname>
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<methodparam><type>string</type><parameter>name</parameter></methodparam>
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<methodparam><type>string</type><parameter>constant_name</parameter></methodparam>
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</methodsynopsis>
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<para>
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Checks whether the given constant exists and is defined.
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Checks whether a constant with the given <parameter>constant_name</parameter>
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is defined.
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</para>
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<para>
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This function works also with <link
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linkend="language.oop5.constants">class constants</link> and <link
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linkend="language.types.enumerations">enum cases</link>.
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</para>
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<note>
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<para>
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If you want to see if a variable exists, use <function>isset</function>
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as <function>defined</function> only applies to <link
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linkend="language.constants">constants</link>. If you want to see if a
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as <function>defined</function> only applies to <link linkend="language.constants">constants</link>. If you want to see if a
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function exists, use <function>function_exists</function>.
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</para>
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</note>
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>name</parameter></term>
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<term><parameter>constant_name</parameter></term>
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<listitem>
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<para>
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The constant name.
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns &true; if the named constant given by <parameter>name</parameter>
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Returns &true; if the named constant given by <parameter>constant_name</parameter>
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has been defined, &false; otherwise.
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</para>
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</refsect1>
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<programlisting role="php">
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<![CDATA[
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<?php
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/* Note the use of quotes, this is important. This example is checking
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/* Note the use of quotes, this is important. This example is checking
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* if the string 'TEST' is the name of a constant named TEST */
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if (defined('TEST')) {
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echo TEST;
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}
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interface bar {
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const test = 'foobar!';
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}
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class foo {
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const test = 'foobar!';
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}
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var_dump(defined('bar::test')); // bool(true)
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var_dump(defined('foo::test')); // bool(true)
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?>
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]]>
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</programlisting>
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</example>
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<example>
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<title>Checking Enum Cases (as of PHP 8.1.0)</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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enum Suit
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{
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case Hearts;
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case Diamonds;
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case Clubs;
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case Spades;
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}
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var_dump(defined('Suit::Hearts')); // bool(true)
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?>
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]]>
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</programlisting>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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