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 — クラスが定義済みかどうかを確認する
説明
bool class_exists
( string $class_name
[, bool $autoload
] )
この関数は指定したクラスが定義されているかどうかを調べます。
返り値
クラス class_name が定義されている場合に TRUE、 それ以外の場合に FALSE を返します。
変更履歴
| バージョン | 説明 |
|---|---|
| 5.0.2 | 定義済みのインターフェイスに対しては TRUE を返さないようになりました。 インターフェイスについては interface_exists() を使用します。 |
| 5.0.0 | autoload パラメータが追加されました。 |
例
例1 class_exists() の例
<?php
// クラスを使用する前に、それが存在するかどうかを調べます
if (class_exists('MyClass')) {
$myclass = new MyClass();
}
?>
例2 autoload パラメータの例
<?php
function __autoload($class)
{
include($class . '.php');
// クラス宣言を含むかどうか確認する
if (!class_exists($class, false)) {
trigger_error("Unable to load class: $class", E_USER_WARNING);
}
}
if (class_exists('MyClass')) {
$myclass = new MyClass();
}
?>
class_exists
Radek @ cz
06-May-2008 10:43
06-May-2008 10:43
richard at richard-sumilang dot com
27-Mar-2008 05:56
27-Mar-2008 05:56
[ >= 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 05:42
01-Jun-2006 05:42
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( $classname, get_declared_classes() ) );
}
?>
06-Apr-2004 09:04
Just a note that at least PHP 4.3.1 seems to crash under some situations if you call class_exists($foo) where $foo is an array (that is, the calling code is incorrect but the error recovery is far from perfect).
anonymous at somewhere dot tld
18-Jul-2003 04:20
18-Jul-2003 04:20
If you have a directory of classes you want to create. (Modules in my instance)... you can do it like that
<?php
if (is_dir($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
25-Jun-2002 03:36
25-Jun-2002 03:36
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 05:48
09-Oct-2001 05:48
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