Automatic loading of php:
Before php5, if we want to use a certain class or class method, it must include or require before it can be used. Every time a class is used, an include needs to be written, which is troublesome
php author To make it simple, it is best to reference a class. If there is no include currently, the system can automatically find the class and automatically introduce it~
So: the __autoload() function came into being.
Usually placed in the application entry class, such as discuz, placed in class_core.php.
Let’s talk about a simple example first:
The first case: the content of file A.php is as follows
<?php class A{ public function __construct(){ echo 'fff'; } } ?> 文件C.php 中内容如下: <?php function __autoload($class) { $file = $class . '.php'; if (is_file($file)) { require_once($file); } } $a = new A(); //这边会自动调用__autoload,引入A.php文件 ?>
The second case: Sometimes I hope to customize autoload and want to give a cooler name for loader, then C .php is changed to the following:
<?php function loader($class) { $file = $class . '.php'; if (is_file($file)) { require_once($file); } } spl_autoload_register('loader'); //注册一个自动加载方法,覆盖原有的__autoload $a = new A(); ?>
The third situation: I hope to be more advanced and use a class to manage automatic loading
<?php class Loader { public static function loadClass($class) { $file = $class . '.php'; if (is_file($file)) { require_once($file); } } } spl_autoload_register(array('Loader', 'loadClass')); $a = new A(); ?>
This is currently the best form.
Usually we put spl_autoload_register(*) in the entry script, that is, quoted from the beginning. For example, the method of discuz below.
if(function_exist('spl_autoload_register')){ spl_autoload_register(array('core','autoload')); //如果是php5以上,存在注册函数,则注册自己写的core类中的autoload为自动加载函数 }else{ function __autoload($class){ //如果不是,则重写php原生函数__autoload函数,让其调用自己的core中函数。 return core::autoload($class); } }
It’s great to put this paragraph at the front of the entry file~