PHPCon Poland 2024

class_exists

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

class_exists查类是否已经定义

说明

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

该函数检查指定的类是否已经定义。

参数

class

类名。名称以不区分大小写的方式匹配。

autoload

如果尚未加载,是否自动加载

返回值

如果 class 是已经定义的类,则返回 true,否则返回 false

示例

示例 #1 class_exists() 示例

<?php
// 在尝试使用前检查类是否存在
if (class_exists('MyClass')) {
$myclass = new MyClass();
}

?>

示例 #2 autoload 参数示例

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

// 检查 include 后是否声明了类
if (!class_exists($class_name, false)) {
throw new
LogicException("Unable to load class: $class_name");
}
});

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

?>

参见

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
up
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.
up
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..
up
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";
up
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!
up
-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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