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96 lines
4.3 KiB
HTML
96 lines
4.3 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>检查某个名称的常量是否存在</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.defined" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">defined</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">defined</span> — <span class="dc-title">检查某个名称的常量是否存在</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.defined-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>defined</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="type">bool</span></div>
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<p class="para rdfs-comment">
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检查该名称的常量是否已定义。
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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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如果你要检查一个变量是否存在，请使用 <span class="function"><a href="isset.html" class="function">isset()</a></span>。
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<span class="function"><strong>defined()</strong></span> 函数仅对 <a href="language.constants.html" class="link">constants</a> 有效。如果你要检测某个函数是否存在，使用 <span class="function"><a href="function_exists.html" class="function">function_exists()</a></span>。
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</p>
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</p></blockquote>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.defined-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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常量的名称。
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</p>
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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.defined-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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如果名称 <code class="parameter">name</code> 的常量已定义，返回 <strong><code>TRUE</code></strong>；未定义则返回 <strong><code>FALSE</code></strong>。
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.defined-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-4533">
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<p><strong>Example #1 检查常量</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 /></span><span style="color: #FF8000">/* Note the use of quotes, this is important. This example is checking<br /> * if the string 'TEST' is the name of a constant named TEST */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">defined</span><span style="color: #007700">(</span><span style="color: #DD0000">'TEST'</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #0000BB">TEST</span><span style="color: #007700">;<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.defined-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="define.html" class="function" rel="rdfs-seeAlso">define()</a> - 定义一个常量</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"><span class="function"><a href="get_defined_constants.html" class="function" rel="rdfs-seeAlso">get_defined_constants()</a> - 返回所有常量的关联数组，键是常量名，值是常量值</span></li>
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<li class="member"><span class="function"><a href="function_exists.html" class="function" rel="rdfs-seeAlso">function_exists()</a> - 如果给定的函数已经被定义就返回 TRUE</span></li>
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<li class="member">章节 <a href="language.constants.html" class="link">Constants</a></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> |