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157 lines
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HTML
157 lines
7.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>定义一个常量</title>
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</head>
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<body class="docs"><div id="layout">
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<div id="layout-content"><div id="function.define" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">define</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">define</span> — <span class="dc-title">定义一个常量</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.define-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>define</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$name</code></span>
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, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$value</code></span>
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[, <span class="methodparam"><span class="type">bool</span> <code class="parameter">$case_insensitive</code><span class="initializer"> = false</span></span>
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] ) : <span class="type">bool</span></div>
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<p class="para rdfs-comment">
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在运行时定义一个常量。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.define-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">name</code></dt>
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<dd>
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<p class="para">
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常量名。
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</p>
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</dd>
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<dt>
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<code class="parameter">value</code></dt>
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<dd>
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<p class="para">
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常量的值；在 PHP 5 中，<code class="parameter">value</code> 必须是标量( <span class="type"><a href="language.types.integer.html" class="type integer">integer</a></span>、
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<span class="type"><a href="language.types.float.html" class="type float">float</a></span>、<span class="type"><a href="language.types.string.html" class="type string">string</a></span>、<span class="type"><a href="language.types.boolean.html" class="type boolean">boolean</a></span>、<strong><code>NULL</code></strong>）在 PHP 7 中还允许是个 <span class="type"><a href="language.types.array.html" class="type array">array</a></span> 的值。
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</p>
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<div class="warning"><strong class="warning">Warning</strong>
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<p class="para">
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常量还可以定义为 <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span> 类型，但并不推荐这样做，因为可能会有不可预知的行为发生。
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</p>
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</div>
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</dd>
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<dt>
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<code class="parameter">case_insensitive</code></dt>
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<dd>
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<p class="para">
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如果设置为 <strong><code>TRUE</code></strong>，该常量则大小写不敏感。默认是大小写敏感的。比如，
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<em>CONSTANT</em> 和 <em>Constant</em> 代表了不同的值。
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</p>
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<blockquote class="note"><p><strong class="note">Note</strong>:
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<p class="para">
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大小写不敏感的常量以小写的方式储存。
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</p>
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</p></blockquote>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.define-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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成功时返回 <strong><code>TRUE</code></strong>， 或者在失败时返回 <strong><code>FALSE</code></strong>。
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</p>
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</div>
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<div class="refsect1 changelog" id="refsect1-function.define-changelog">
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<h3 class="title">更新日志</h3>
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<p class="para">
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<table class="doctable informaltable">
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<thead>
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<tr>
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<th>版本</th>
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<th>说明</th>
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</tr>
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</thead>
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<tbody class="tbody">
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<tr>
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<td>7.0.0</td>
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<td>
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允许 <span class="type"><a href="language.types.array.html" class="type array">array</a></span> 的值。
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</td>
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</tr>
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</tbody>
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</table>
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.define-examples">
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<h3 class="title">范例</h3>
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<p class="para">
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<div class="example" id="example-4532">
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<p><strong>Example #1 定义常量</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br />define</span><span style="color: #007700">(</span><span style="color: #DD0000">"CONSTANT"</span><span style="color: #007700">, </span><span style="color: #DD0000">"Hello world."</span><span style="color: #007700">);<br />echo </span><span style="color: #0000BB">CONSTANT</span><span style="color: #007700">; </span><span style="color: #FF8000">// 输出 "Hello world."<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">Constant</span><span style="color: #007700">; </span><span style="color: #FF8000">// 输出 "Constant" 并导致 Notice<br /><br /></span><span style="color: #0000BB">define</span><span style="color: #007700">(</span><span style="color: #DD0000">"GREETING"</span><span style="color: #007700">, </span><span style="color: #DD0000">"Hello you."</span><span style="color: #007700">, </span><span style="color: #0000BB">true</span><span style="color: #007700">);<br />echo </span><span style="color: #0000BB">GREETING</span><span style="color: #007700">; </span><span style="color: #FF8000">// 输出 "Hello you."<br /></span><span style="color: #007700">echo </span><span style="color: #0000BB">Greeting</span><span style="color: #007700">; </span><span style="color: #FF8000">// 输出 "Hello you."<br /><br />// PHP 7 起就可以运行了<br /></span><span style="color: #0000BB">define</span><span style="color: #007700">(</span><span style="color: #DD0000">'ANIMALS'</span><span style="color: #007700">, array(<br /> </span><span style="color: #DD0000">'dog'</span><span style="color: #007700">,<br /> </span><span style="color: #DD0000">'cat'</span><span style="color: #007700">,<br /> </span><span style="color: #DD0000">'bird'<br /></span><span style="color: #007700">));<br />echo </span><span style="color: #0000BB">ANIMALS</span><span style="color: #007700">[</span><span style="color: #0000BB">1</span><span style="color: #007700">]; </span><span style="color: #FF8000">// 输出 "cat"<br /><br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</div>
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</p>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.define-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
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<ul class="simplelist">
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<li class="member"><span class="function"><a href="defined.html" class="function" rel="rdfs-seeAlso">defined()</a> - 检查某个名称的常量是否存在</span></li>
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<li class="member"><span class="function"><a href="constant.html" class="function" rel="rdfs-seeAlso">constant()</a> - 返回一个常量的值</span></li>
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<li class="member"><a href="language.constants.html" class="link">Constants</a>这一节</li>
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</ul>
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</p>
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</div>
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</div></div></div></body></html> |