class_exists

(PHP 4, PHP 5, PHP 7)

class_exists — 检查类是否已定义

说明

bool class_exists ( string $class_name [, bool $autoload = true ] )

检查指定的类是否已定义。

参数

class_name: 类名。名字的匹配是大小写不敏感的。
autoload: 是否默认调用 __autoload。

返回值

如果由 class_name 所指的类已经定义，此函数返回 TRUE ，否则返回 FALSE 。

更新日志

版本	说明
5.0.2	不再为已定义的 interface 返回 `TRUE` 。请使用 interface_exists() 。
5.0.0	增加参数 `autoload`。

范例

Example #1 class_exists() 例子

  <?php
 // 使用前检查类是否存在
 if ( class_exists ( 'MyClass' )) {
     $myclass  = new  MyClass ();
}

 ?>

Example #2 autoload parameter 例子

  <?php
 function  __autoload ( $class )
{
    include( $class  .  '.php' );

     // Check to see whether the include declared the class
     if (! class_exists ( $class ,  false )) {
         trigger_error ( "Unable to load class:  $class " ,  E_USER_WARNING );
    }
}

if ( class_exists ( 'MyClass' )) {
     $myclass  = new  MyClass ();
}

 ?>

参见

function_exists() - 如果给定的函数已经被定义就返回 TRUE
interface_exists() - 检查接口是否已被定义
get_declared_classes() - 返回由已定义类的名字所组成的数组

用户评论:

[#1] rn at alpha9marketing dot com [2014-04-06 17:55:57]

Beware: class_exists is case-INsensitive, as is class instantiation.

php > var_dump(class_exists("DomNode"));
bool(true)
php > var_dump(class_exists("DOMNode"));
bool(true)
php > var_dump(class_exists("DOMNodE"));
bool(true)
php > $x = new DOMNOdE();
php > var_dump(get_class($x));
string(7) "DOMNode"

(tested with PHP 5.5.10 on Linux)

This can cause some headaches in correlating class names to file names, especially on a case-sensitive file system.

[#2] spam at wikicms dot org [2013-12-09 14:43:23]

Hi guys!
Be careful and don't forget about second boolean argument $autoload (TRUE by default) when check exists class after spl_autoload_register. Propose short example
file second.php
<?php class Second {} ?>
file index.php
<?php class First { function first($class, $bool) { spl_autoload_register( function($class) { require strtolower($class) . '.php'; }); echo class_exists($class, $bool)?'Exist!!!!':'Not exist!'; } } new First($class = 'Second', $bool = true); //Exist!!!! new First($class = 'Second', $bool = false); //Not exist! ?>
Because __autoload executing much earlier than boolean returned, imho..

[#3] giunta dot gaetano at gmail dot com [2013-10-31 17:28:39]

If you are using aliasing to import namespaced classes, take care that class_exists will not work using the short, aliased class name - apparently whenever a class name is used as string, only the full-namespace version can be used

use a\namespaced\classname as coolclass;

class_exists( 'coolclass' ) => false

[#4] toocoolone at gmail dot com [2012-02-14 06:47:11]

I'm running PHP 5.3.4 on Windows 7 and had some difficulty autoloading classes using class_exists(). In my case, when I checked for the class and it didn't exist, class_exists automatically threw a system Exception. I was also throwing my own exception resulting in an uncaught exception.

<?php $include_path = array( '/include/this/dir', '/include/this/one/too' ); set_include_path( $include_path ); spl_autoload_register(); try { if( ! file_exists( 'myfile.php' ) ) { throw new MyException('Doh!'); } include( 'myfile.php' ); } catch( MyException $e ) { echo $e->getMessage(); } $classname = 'NonExistentClass'; try { if( ! class_exists( $classname ) ) { throw new MyException('Double Doh!'); } $var = new $classname(); } catch( MyException $e ) { echo $e->getMessage(); } ?>

By registering an additional autoload handler function that did nothing, I was able to stop throwing the extra Exception and only throw my own.

<?php $include_path = array( '/include/this/dir', '/include/this/one/too' ); set_include_path( $include_path ); spl_autoload_register(); spl_autoload_register( 'myAutoLoad' ); // Add these two and no worries... function myAutoLoad() {} ?>

Found this buried in some search results. I don't remember the page URL but if it would have been here it might have saved me some time!

[#5] Klaus [2010-04-28 04:21:39]

If you recursively load several classes inside an autoload function (or mix manual loading and autoloading), be aware that class_exists() (as well as get_declared_classes()) does not know about classes previously loaded during the *current* autoload invocation.

Apparently, the internal list of declared classes is only updated after the autoload function is completed.

[#6] azrael dot com at gmail dot com [2008-12-11 16:14:18]

If spl_autoload_register() had been called, then function will try autoload class if it does not exists.

Use instead
<?php in_array($class_name, get_declared_classes()); ?>

[#7] Radek @ cz [2008-05-05 18:43:05]

If you want to combat many class includes effectively, define your own autoloader function and spl_autoload_register() that autoloader.

[#8] richard at richard-sumilang dot com [2008-03-27 00:56:55]

[ >= PHP 5.3]

If you are checking if a class exists that is in a specific namespace then you have to pass in the full path to the class:

echo (class_exists("com::richardsumilang::common::MyClass")) ? "Yes" : "No";

[#9] anonymous at somewhere dot tld [2003-07-17 12:20:31]

If you have a directory of classes you want to create. (Modules in my instance)... you can do it like that

<?php if (is_dir($this->MODULE_PATH) && $dh = opendir($this->MODULE_PATH)) { while (($file = readdir($dh)) !== false) { if (preg_match("/(Mod[a-zA-Z0-9]+).php/", $file, $matches)>0) { // include and create the class require_once($this->MODULE_PATH."/".$file); $modules[] = new $matches[1](); } } } else { exit; } ?>

//---
Here the rule is that all modules are on the form
ModModulename.php and that the class has the same name as the file.
The $modules array has all the classes initialized after this code