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128 lines
3.2 KiB
XML
128 lines
3.2 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<!-- EN-Revision: 85c47f89f35f927d7c7ad23235c830dc4b514ddd Maintainer: avenger Status: ready -->
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<!-- CREDITS: mowangjuanzi -->
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<refentry xml:id="function.array-key-first" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<refnamediv>
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<refname>array_key_first</refname>
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<refpurpose>获取指定数组的第一个键</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 class="union"><type>int</type><type>string</type><type>null</type></type><methodname>array_key_first</methodname>
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<methodparam><type>array</type><parameter>array</parameter></methodparam>
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</methodsynopsis>
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<para>
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不影响到数组内部指针，取得指定数组的 <parameter>array</parameter>
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第一个键。
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</para>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<variablelist>
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<varlistentry>
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<term><parameter>array</parameter></term>
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<listitem>
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<para>
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要操作的数组。
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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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 <parameter>array</parameter> 不是空的，返回第一个键，否则返回 &null;。
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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 xml:id="array_key_first.example.basic">
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<title><function>array_key_first</function> 基本用法</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$array = ['a' => 1, 'b' => 2, 'c' => 3];
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$firstKey = array_key_first($array);
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var_dump($firstKey);
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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string(1) "a"
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]]>
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</screen>
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</example>
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</para>
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</refsect1>
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<refsect1 role="notes">
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&reftitle.notes;
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<tip>
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<simpara>
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在 PHP 7.3.0 之前，有几种方式可以实现该功能。可以使用
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<function>array_keys</function> 函数，但是性能会比较低。也可以使用
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<function>reset</function> 和 <function>key</function>
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函数，但这可能会影响内部数组指针。实现该功能的 polyfill 写法如下:
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</simpara>
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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 (!function_exists('array_key_first')) {
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function array_key_first(array $arr) {
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foreach($arr as $key => $unused) {
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return $key;
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}
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return NULL;
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}
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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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</tip>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<simplelist>
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<member><function>array_first</function></member>
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<member><function>array_key_last</function></member>
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<member><function>reset</function></member>
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</simplelist>
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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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