PHP 5.4.33 Released

class_exists

(PHP 4, PHP 5)

class_existsChecks if the class has been defined

Description

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

This function checks whether or not the given class has been defined.

Parameters

class_name

The class name. The name is matched in a case-insensitive manner.

autoload

Whether or not to call __autoload by default.

Return Values

Returns TRUE if class_name is a defined class, FALSE otherwise.

Changelog

Version Description
5.0.2 No longer returns TRUE for defined interfaces. Use interface_exists().

Examples

Example #1 class_exists() example

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

?>

Example #2 autoload parameter example

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

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

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

?>

See Also

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User Contributed Notes 11 notes

up
5
spam at wikicms dot org
9 months ago
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..
up
2
richard at richard-sumilang dot com
6 years ago
[ >= 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";
up
1
azrael dot com at gmail dot com
5 years ago
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());
?>
up
2
rn at alpha9marketing dot com
5 months ago
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.
up
1
anonymous at somewhere dot tld
11 years ago
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
up
1
giunta dot gaetano at gmail dot com
10 months ago
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
up
1
toocoolone at gmail dot com
2 years ago
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
/**
* Set my include path here
*/
$include_path = array( '/include/this/dir', '/include/this/one/too' );
set_include_path( $include_path );
spl_autoload_register();
/**
* Assuming I have my own custom exception handler (MyException) let's
* try to see if a file exists.
*/
try {
    if( !
file_exists( 'myfile.php' ) ) {
        throw new
MyException('Doh!');
    }
    include(
'myfile.php' );
}
catch(
MyException $e ) {
    echo
$e->getMessage();
}
/**
* The above code either includes myfile.php or throws the new MyException
* as expected. No problem right? The same should be true of class_exists(),
* right? So then...
*/
$classname = 'NonExistentClass';
try {
    if( !
class_exists( $classname ) ) {
        throw new
MyException('Double Doh!');
    }
   
$var = new $classname();
}
catch(
MyException $e ) {
    echo
$e->getMessage();
}
/**
* Should throw a new instance of MyException. But instead I get an
* uncaught LogicException blah blah blah for the default Exception
* class AND MyException. I only catch MyException so we've got on
* uncaught resulting in the dreaded LogicException error.
*/
?>

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
/**
* Set my include path here
*/
$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() {}
/**
* By registering the additional custom autoload function that does nothing
* class_exists() returns only boolean and does NOT throw an uncaught Exception
*/
?>

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!
up
1
Klaus
4 years ago
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.
up
0
Anonymous
5 years ago
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.
up
0
Radek @ cz
6 years ago
If you want to combat many class includes effectively, define your own autoloader function and spl_autoload_register() that autoloader.
up
-4
Anonymous
3 years ago
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
?>
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