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102 lines
5.8 KiB
HTML
102 lines
5.8 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>返回一个常量的值</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.constant" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">constant</h1>
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<p class="verinfo">(PHP 4 >= 4.0.4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">constant</span> — <span class="dc-title">返回一个常量的值</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.constant-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>constant</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"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span></div>
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<p class="simpara">
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通过 <code class="parameter">name</code> 返回常量的值。
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</p>
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<p class="simpara">
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当你不知道常量名，却需要获取常量的值时，<span class="function"><strong>constant()</strong></span> 就很有用了。也就是常量名储存在一个变量里，或者由函数返回常量名。
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</p>
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<p class="simpara">
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该函数也适用 <a href="language.oop5.constants.html" class="link">class constants</a>。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.constant-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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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.constant-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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返回常量的值。如果常量未定义则返回 <strong><code>NULL</code></strong>。
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</p>
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</div>
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<div class="refsect1 errors" id="refsect1-function.constant-errors">
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<h3 class="title">错误／异常</h3>
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<p class="para">
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如果常量未定义，会产生一个 <strong><code>E_WARNING</code></strong> 级别的错误。
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</p>
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</div>
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<div class="refsect1 examples" id="refsect1-function.constant-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-4531">
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<p><strong>Example #1 <span class="function"><strong>constant()</strong></span> 的例子</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 /><br />define</span><span style="color: #007700">(</span><span style="color: #DD0000">"MAXSIZE"</span><span style="color: #007700">, </span><span style="color: #0000BB">100</span><span style="color: #007700">);<br /><br />echo </span><span style="color: #0000BB">MAXSIZE</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">constant</span><span style="color: #007700">(</span><span style="color: #DD0000">"MAXSIZE"</span><span style="color: #007700">); </span><span style="color: #FF8000">// same thing as the previous line<br /><br /><br /></span><span style="color: #007700">interface </span><span style="color: #0000BB">bar </span><span style="color: #007700">{<br /> const </span><span style="color: #0000BB">test </span><span style="color: #007700">= </span><span style="color: #DD0000">'foobar!'</span><span style="color: #007700">;<br />}<br /><br />class </span><span style="color: #0000BB">foo </span><span style="color: #007700">{<br /> const </span><span style="color: #0000BB">test </span><span style="color: #007700">= </span><span style="color: #DD0000">'foobar!'</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">$const </span><span style="color: #007700">= </span><span style="color: #DD0000">'test'</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">constant</span><span style="color: #007700">(</span><span style="color: #DD0000">'bar::'</span><span style="color: #007700">. </span><span style="color: #0000BB">$const</span><span style="color: #007700">)); </span><span style="color: #FF8000">// string(7) "foobar!"<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">constant</span><span style="color: #007700">(</span><span style="color: #DD0000">'foo::'</span><span style="color: #007700">. </span><span style="color: #0000BB">$const</span><span style="color: #007700">)); </span><span style="color: #FF8000">// string(7) "foobar!"<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.constant-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="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"><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> |