PHP: class_exists

Description

bool class_exists ( string class_name [, bool autoload] )

This function returns TRUE if the class given by class_name has been defined, FALSE otherwise.

Example 1. class_exists() example

<?php // Check the class exists before trying to use it if (class_exists('MyClass')) { $myclass = new MyClass(); } ?>

class_exists() will attempt to call __autoload by default, if you don't want class_exists() to call __autoload, you can set the parameter autoload to FALSE.

Example 2. autoload parameter example

<?php function __autoload($class) { include($class . '.php'); // Check to see if 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(); } ?>

Note: The autoload parameter was added in PHP 5

User Contributed Notes
class_exists

andrey at php dot net
24-Oct-2004 06:43


In 5.0.0 and 5.0.1 there was no interface_exists() and in these versions class_exists() used to return TRUE for known interfaces. Starting 5.0.2 this is no more.

06-Apr-2004 07:04


Just a note that at least PHP 4.3.1 seems to crash under some situations if you call class_exists($foo) where $foo is an array (that is, the calling code is incorrect but the error recovery is far from perfect).

anonymous at somewhere dot tld
17-Jul-2003 02:20


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

cristiano at aspatech dot com dot br
24-Jun-2002 01:36


This can be veeeery usefull if you use classes that uses other classes, which can be used in your front end. In other words, when you lost the control of which classes are declared in which point of the application, that can generate the "Cannot redeclare class". Use like





<?php


if ( !class_exists( "YourClass" ) ) {





    class YourClass {


        //your code


    }


}


?>





Thats it... Resolve all your problems =)

spamless_blair at nb dot net
09-Oct-2001 03:48


I have a script that includes various class libraries depending on what is contained in the constant _INCLUDE_LIST which is a comma-delimited string.





define('_INCLUDE_LIST', 'CORE, LIB_DATA, LIB_EMAIL');





I use class_exists() to determine if a class definition has been included before creating an instance of it.





if(class_exists('CMySQLConnection')) $oData = new CMySQLConnection;





Hope it is helpful for someone!





-Jason Garber


IonZoft.com

emurano at optushome dot com dot au
09-Mar-2001 02:35


Multiple inclusion protection can be achieved in php3 and for non class related code, for example:





<?php


if(!defined("_SOME_UNIQUE_CONSTANT_")) {


define("_SOME_UNIQUE_CONSTANT_",TRUE);





// Your protected code here





}


?>





Make sure that you use a different constant for each protected piece of code.  Generally this is used on a file per file basis. Just #ifndef in C!