class_alias
It might not be obvious to some, but whenever you reference a namespace in a string, each backslash must be escaped with another backslash because of how PHP handles strings.
<?php
class_exists('\\Zend_Registry'); // return true
?>
class_exists
(PHP 4, PHP 5)
class_exists — Verifica si la clase ha sido definida
Descripción
bool class_exists
( string $class_name
[, bool $autoload = true
] )
Esta función verifica si la clase dada ha sido definida o no.
Parámetros
- class_name
-
El nombre de la clase. El nombre es coincidido de manera insensible a mayúsculas y minúsculas.
- autoload
-
Indica si ha de llamarse __autoload o no de forma predeterminada.
Valores devueltos
Devuelve TRUE si class_name es una clase definida, FALSE de lo contrario.
Historial de cambios
| Versión | Descripción |
|---|---|
| 5.0.2 | Ya no devuelve TRUE para interfaces definidas. En ese caso se debe usar interface_exists(). |
| 5.0.0 | Se añadió el parámetro autoload. |
Ejemplos
Example #1 Ejemplo de class_exists()
<?php
// Verificar que la clase exista antes de usarla
if (class_exists('MiClase')) {
$mi_clase = new MiClase();
}
?>
Example #2 Ejemplo del parámetro autoload
<?php
function __autoload($clase)
{
include($clase . '.php');
// Verificar si la sentencia include declaró la clase
if (!class_exists($clase, false)) {
trigger_error("No es posible cargar la clase: $clase", E_USER_WARNING);
}
}
if (class_exists('MiClase')) {
$mi_clase = new MiClase();
}
?>
Ver también
- function_exists() - Devuelve TRUE si la función dada ha sido definida
- interface_exists() - Comprueba si una interfaz ha sido definida
- get_declared_classes() - Devuelve una matriz con los nombres de las clases definidas
add a note
User Contributed Notes
class_exists
Anonymous
08-Mar-2011 06:21
myb at mikebevz dot com
23-Sep-2010 01:50
I've got a problem, which I can't solve.
Let's assume that class Zend_Registry exists in global namespace.
---
namespace myNs;
class SomeClass {
public function MyFunc() {
class_exists('Zend_Registry'); // return false
class_exists('\Zend_Registry'); // return false
class_exists('::Zend_Registry'); // return false
}
}
---
How would I check for a class, which exists outside of myNs?
Klaus
28-Apr-2010 11:21
If you recursively load several classes inside an autoload function (or mix manual loading and autoloading), be aware that class_exists() (as well as get_declared_classes()) does not know about classes previously loaded during the *current* autoload invocation.
Apparently, the internal list of declared classes is only updated after the autoload function is completed.
azrael dot com at gmail dot com
12-Dec-2008 12:14
If spl_autoload_register() had been called, then function will try autoload class if it does not exists.
Use instead
<?php
in_array($class_name, get_declared_classes());
?>
Anonymous
29-Nov-2008 06:27
If you planned to use utf-8 in classes or variables names, remember that locale has to be properly set firstly, e.g.
<?php
locale (LC_ALL, 'ru_RU.UTF-8');
?>
or it turn into errors.
Radek @ cz
06-May-2008 01:43
If you want to combat many class includes effectively, define your own autoloader function and spl_autoload_register() that autoloader.
richard at richard-sumilang dot com
27-Mar-2008 08:56
[ >= 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 08:42
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( $classname, get_declared_classes() ) );
}
?>
06-Apr-2004 12:04
Just a note that at least PHP 4.3.1 seems to crash under some situations if you call class_exists($foo) where $foo is an array (that is, the calling code is incorrect but the error recovery is far from perfect).
anonymous at somewhere dot tld
17-Jul-2003 07:20
If you have a directory of classes you want to create. (Modules in my instance)... you can do it like that
<?php
if (is_dir($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