PHPCon Poland 2024

class_exists

(PHP 4, PHP 5, PHP 7, PHP 8)

class_existsChecks if the class has been defined

Description

class_exists(string $class, bool $autoload = true): bool

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

Parameters

class

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

autoload

Whether to autoload if not already loaded.

Return Values

Returns true if class is a defined class, false otherwise.

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
spl_autoload_register
(function ($class_name) {
include
$class_name . '.php';

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

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

?>

See Also

add a note

User Contributed Notes 9 notes

up
50
giunta dot gaetano at gmail dot com
10 years 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
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10
info at ensostudio dot ru
3 years ago
Note: class_exists() check only classes!
<?php
interface DemoInterface {};
var_dump(class_exists('DemoInterface')); // false
trait DemoTrait {};
var_dump(class_exists('DemoTrait')); // false
class DemoClass {};
var_dump(class_exists('DemoClass')); // true
?>

Common function:
<?php
/**
* Checks if the class/trait/interface has been defined.
*
* @param string $name The case-insensitive name of class/trait/interface
* @param bool $autoload Whether to call spl_autoload()
* @return bool
*/
function structure_exists(string $name, bool $autoload = true): bool
{
return
class_exists($name, $autoload)
||
interface_exists($name, $autoload)
||
trait_exists($name, $autoload);
}
?>
up
15
rn at alpha9marketing dot com
10 years 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.
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13
Klaus
14 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
12
spam at wikicms dot org
10 years 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..
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10
richard at richard-sumilang dot com
16 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";
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2
anonymous at somewhere dot tld
20 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
0
toocoolone at gmail dot com
12 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!
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-13
azrael dot com at gmail dot com
15 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());
?>
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