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* 翻译 * 更新 * 追加新的 * Update http.xml * Update http.xml * Update else.xml Co-authored-by: DAI JIE <daijie@php.net>
81 lines
2.5 KiB
XML
81 lines
2.5 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<!-- $Author$ -->
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<!-- EN-Revision: 690c3ea7c7d416c55e2c54d90bfd1f7f4d489288 Maintainer: dallas Status: ready -->
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<sect1 xml:id="control-structures.else" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>else</title>
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<?phpdoc print-version-for="else"?>
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<para>
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经常需要在满足某个条件时执行一条语句，而在不满足该条件时执行其它语句，这正是
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<literal>else</literal> 的功能。<literal>else</literal> 延伸了
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<literal>if</literal> 语句，可以在 <literal>if</literal>
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语句中的表达式的值为 &false; 时执行语句。例如以下代码在
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<varname>$a</varname> 大于 <varname>$b</varname> 时显示
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<computeroutput>a is bigger than b</computeroutput>，反之则显示
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<computeroutput>a is NOT bigger than b</computeroutput>：
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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if ($a > $b) {
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echo "a is greater than b";
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} else {
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echo "a is NOT greater than b";
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}
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?>
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]]>
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</programlisting>
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</informalexample>
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<literal>else</literal> 语句仅在 <literal>if</literal> 以及
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<literal>elseif</literal>（如果有的话）语句中的表达式的值为
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&false; 时执行（参见 <link
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linkend="control-structures.elseif">elseif</link>）。
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</para>
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<note>
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<title>悬挂的 else</title>
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<para>
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在多层嵌套 <literal>if</literal>-<literal>else</literal> 语句的情况下，
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<literal>else</literal> 总是与最近的 <literal>if</literal> 进行关联。
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$a = false;
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$b = true;
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if ($a)
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if ($b)
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echo "b";
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else
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echo "c";
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?>
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]]>
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</programlisting>
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</informalexample>
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虽然存在缩进（对 PHP 来说，无关紧要）， 但是 <literal>else</literal> 还是与 <literal>if ($b)</literal>
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进行关联，所以以上示例不会产生任何输出。虽然可以依赖此特性，但是推荐使用花括号，避免潜在的歧义问题。
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</para>
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</note>
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</sect1>
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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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