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145 lines
3.4 KiB
XML
145 lines
3.4 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<!-- EN-Revision: 36e1d917ef7be36e8b4ff5193b456390061f2e21 Maintainer: daijie Status: ready -->
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<!-- CREDITS: mowangjuanzi, Luffy -->
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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>检查给定名称的常量是否存在</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>constant_name</parameter></methodparam>
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</methodsynopsis>
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<para>
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检查给定 <parameter>constant_name</parameter> 的常量是否已定义。
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</para>
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<para>
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此函数也可以跟<link
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linkend="language.oop5.constants">类常量</link>和 <link
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linkend="language.types.enumerations">Enum 枚举</link> 一起工作。
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</para>
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<note>
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<para>
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如果你要检查一个变量是否存在，请使用 <function>isset</function>。
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<function>defined</function> 函数仅对 <link linkend="language.constants">常量</link>
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有效。如果你要检测某个函数是否存在，使用 <function>function_exists</function>。
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</para>
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</note>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>constant_name</parameter></term>
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<listitem>
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<para>
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常量的名称。
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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如果名称 <parameter>constant_name</parameter> 的常量已定义，返回 &true;；未定义则返回 &false;。
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</para>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title>检查常量</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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/* 注意引号的使用，这很重要。这个例子是检查
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* 如果字符串 'TEST' 是 TEST 常量的名称 */
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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>检测 Enum Cases（自 PHP 8.1.0 起）</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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</example>
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</para>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>define</function></member>
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<member><function>constant</function></member>
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<member><function>get_defined_constants</function></member>
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<member><function>function_exists</function></member>
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<member>关于<link linkend="language.constants">常量</link>的章节</member>
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</simplelist>
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</para>
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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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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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