📄 function.class-exists.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Checks if the class has been defined</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.call-user-method.html">call_user_method</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.get-class-methods.html">get_class_methods</a></div> <div class="up"><a href="ref.classobj.html">Classes/Object Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.class-exists" class="refentry"> <div class="refnamediv"> <h1 class="refname">class_exists</h1> <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">class_exists</span> — <span class="dc-title">Checks if the class has been defined</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type">bool</span> <span class="methodname"><b><b>class_exists</b></b></span> ( <span class="methodparam"><span class="type">string</span> <tt class="parameter">$class_name</tt></span> [, <span class="methodparam"><span class="type">bool</span> <tt class="parameter">$autoload</tt></span> ] )</div> <p class="para rdfs-comment"> This function checks whether or not the given class has been defined. </p> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <span class="term"><i><tt class="parameter">class_name</tt></i></span> <dd> <p class="para"> The class name. The name is matched in a case-insensitive manner. </p> </dd> </dt> <dt> <span class="term"><i><tt class="parameter">autoload</tt></i></span> <dd> <p class="para"> Whether or not to call <a href="language.oop5.autoload.html" class="link">__autoload</a> by default. Defaults to <b><tt>TRUE</tt></b>. </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> Returns <b><tt>TRUE</tt></b> if <i><tt class="parameter">class_name</tt></i> is a defined class, <b><tt>FALSE</tt></b> otherwise. </p> </div> <div class="refsect1 changelog"> <h3 class="title">ChangeLog</h3> <p class="para"> <table class="informaltable"> <colgroup> <thead valign="middle"> <tr valign="middle"> <th colspan="1">Version</th> <th colspan="1">Description</th> </tr> </thead> <tbody valign="middle" class="tbody"> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">5.0.2</td> <td colspan="1" rowspan="1" align="left"> No longer returns <b><tt>TRUE</tt></b> for defined interfaces. Use <a href="function.interface-exists.html" class="function">interface_exists()</a>. </td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">5.0.0</td> <td colspan="1" rowspan="1" align="left"> The <i><tt class="parameter">autoload</tt></i> parameter was added. </td> </tr> </tbody> </colgroup> </table> </p> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example"> <p><b>Example #1 <b>class_exists()</b> example</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Check that the class exists before trying to use it<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">$myclass </span><span style="color: #007700">= new </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> <div class="example"> <p><b>Example #2 <i><tt class="parameter">autoload</tt></i> parameter example</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">__autoload</span><span style="color: #007700">(</span><span style="color: #0000BB">$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: $class"</span><span style="color: #007700">, </span><span style="color: #0000BB">E_USER_WARNING</span><span style="color: #007700">);<br /> }<br />}<br /><br />if (</span><span style="color: #0000BB">class_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'MyClass'</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$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></span></code></div> </div> </div> </p> </div> <div class="refsect1 seealso"> <h3 class="title">See Also</h3> <p class="para"> <ul class="simplelist"> <li class="member"><a href="function.function-exists.html" class="function" rel="rdfs-seeAlso">function_exists()</a></li> <li class="member"><a href="function.interface-exists.html" class="function" rel="rdfs-seeAlso">interface_exists()</a></li> <li class="member"><a href="function.get-declared-classes.html" class="function" rel="rdfs-seeAlso">get_declared_classes()</a></li> </ul> </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.call-user-method.html">call_user_method</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.get-class-methods.html">get_class_methods</a></div> <div class="up"><a href="ref.classobj.html">Classes/Object Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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