call_user_method
If you want to combat many class includes effectively, define your own autoloader function and spl_autoload_register() that autoloader.
class_exists
(PHP 4, PHP 5)
class_exists — Verifica se una classe è stata definita
Descrizione
bool class_exists
( string $nome_classe
[, bool $autoload
] )
Questa funzione restituisce TRUE se la classe indicata dal parametro nome_classe è stata definita, altrimenti restituisce FALSE .
Example #1 Esempio di uso di class_exists()
<?php
// Verifica se la classe esiste prima di richiamarla
if (class_exists('MyClass')) {
$myclass = new MyClass();
}
?>
class_exists(), per default, tenta di eseguire __autoload, se non si desidera che class_exists() esegua __autoload(), impostare il parametro autoload a FALSE.
Example #2 Esempio di uso di autoload
<?php
function __autoload($class)
{
include($class . '.php');
// Check to see it the include defined the class
if ( !class_exists($class, false) ) {
trigger_error("Unable to load class $class", E_USER_ERROR);
}
}
if( class_exists('MyClass') ) {
$myclass = new MyClass();
}
?>
Nota: Il parametro autoload è stato aggiunto in PHP 5
Vedere anche interface_exists() e get_declared_classes().
add a note
User Contributed Notesclass_exists
Radek @ cz
05-May-2008 06:43
05-May-2008 06:43
richard at richard-sumilang dot com
27-Mar-2008 01:56
27-Mar-2008 01:56
[ >= 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";
Frayja
01-Jun-2006 01:42
01-Jun-2006 01:42
Like someone else pointed out class_exists() is case-INsensitive.
Using in_array() which is case-sensitive, the following function is a case-sensitive version of class_exists().
<?php
function class_exists_sensitive( $classname )
{
return ( class_exists( $classname ) && in_array( $classname, get_declared_classes() ) );
}
?>
06-Apr-2004 05:04
Just a note that at least PHP 4.3.1 seems to crash under some situations if you call class_exists($foo) where $foo is an array (that is, the calling code is incorrect but the error recovery is far from perfect).
anonymous at somewhere dot tld
17-Jul-2003 12:20
17-Jul-2003 12:20
If you have a directory of classes you want to create. (Modules in my instance)... you can do it like that
<?php
if (is_dir($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 11:36
24-Jun-2002 11:36
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 01:48
09-Oct-2001 01:48
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