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137 lines
6.7 KiB
HTML
137 lines
6.7 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>检查类是否已定义</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.class-exists" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">class_exists</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">class_exists</span> — <span class="dc-title">检查类是否已定义</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.class-exists-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>class_exists</strong></span>
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( <span class="methodparam"><span class="type">string</span> <code class="parameter">$class_name</code></span>
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[, <span class="methodparam"><span class="type">bool</span> <code class="parameter">$autoload</code><span class="initializer"> = true</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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检查指定的类是否已定义。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.class-exists-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">class_name</code></dt>
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<dd>
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<p class="para">
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类名。名字的匹配是不分区大小写的。
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</p>
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</dd>
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<dt>
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<code class="parameter">autoload</code></dt>
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<dd>
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<p class="para">
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是否默认调用 <a href="language.oop5.autoload.html" class="link">__autoload</a>。
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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.class-exists-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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如果由 <code class="parameter">class_name</code>
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所指的类已经定义，此函数返回
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<strong><code>TRUE</code></strong>，否则返回 <strong><code>FALSE</code></strong>。
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</p>
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</div>
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<div class="refsect1 changelog" id="refsect1-function.class-exists-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>5.0.2</td>
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<td>
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不再为已定义的 interface 返回 <strong><code>TRUE</code></strong>。请使用
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<span class="function"><a href="interface_exists.html" class="function">interface_exists()</a></span>。
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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.class-exists-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-6131">
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<p><strong>Example #1 <span class="function"><strong>class_exists()</strong></span> 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 /></span><span style="color: #FF8000">// 使用前检查类是否存在<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">class_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'MyClass'</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$myclass </span><span style="color: #007700">= new </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #0000BB">?></span>
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</span>
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</pre></div>
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</div>
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</div>
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<div class="example" id="example-6132">
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<p><strong>Example #2 <code class="parameter">autoload</code> parameter 例子</strong></p>
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<div class="example-contents">
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<div class="phpcode"><pre><span style="color: #000000">
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<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">__autoload</span><span style="color: #007700">(</span><span style="color: #0000BB">$class</span><span style="color: #007700">)<br />{<br /> include(</span><span style="color: #0000BB">$class </span><span style="color: #007700">. </span><span style="color: #DD0000">'.php'</span><span style="color: #007700">);<br /><br /> </span><span style="color: #FF8000">// Check to see whether the include declared the class<br /> </span><span style="color: #007700">if (!</span><span style="color: #0000BB">class_exists</span><span style="color: #007700">(</span><span style="color: #0000BB">$class</span><span style="color: #007700">, </span><span style="color: #0000BB">false</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">trigger_error</span><span style="color: #007700">(</span><span style="color: #DD0000">"Unable to load class: </span><span style="color: #0000BB">$class</span><span style="color: #DD0000">"</span><span style="color: #007700">, </span><span style="color: #0000BB">E_USER_WARNING</span><span style="color: #007700">);<br /> }<br />}<br /><br />if (</span><span style="color: #0000BB">class_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'MyClass'</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$myclass </span><span style="color: #007700">= new </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">();<br />}<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.class-exists-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="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"><span class="function"><a href="interface_exists.html" class="function" rel="rdfs-seeAlso">interface_exists()</a> - 检查接口是否已被定义</span></li>
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<li class="member"><span class="function"><a href="get_declared_classes.html" class="function" rel="rdfs-seeAlso">get_declared_classes()</a> - 返回由已定义类的名字所组成的数组</span></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> |