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php's Automatic loading:
Before php5, if we wanted to use a certain class or class method, we had to include or require, it can be used later. Every time you use a class, you need to write an include. Please
The php author wants to make it simple. It is best to reference a class. If there is no include currently, the system can automatically Find this 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 situation: The content of file A.php is as follows
<?php class A{ public function construct(){ echo 'fff'; } } ?>
The content of file C.php is as follows :
<?php function autoload($class) { $file = $class . '.php'; if (is_file($file)) { require_once($file); } } $a = new A(); //这边会自动调用autoload,引入A.php文件 ?>
The second situation: Sometimes I hope to customize autoload and give a cooler name for loader, then C.php should be changed to the following:
<?php function loader($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')); $a = new A(); ?>
This is currently the best form.
Usually we put spl_autoload_register(*) in the entry script, that is, quoted from the beginning. For example, what discuz does below.
if(function_exist('spl_autoload_register')){ spl_autoload_register(array('core','autoload')); //如果是php5以上,存在注册函数,则注册自己写的core类中的autoload为自动加载函数 }else{ function autoload($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); } }
This paragraph is thrown at the front of the entry file, which is naturally excellent~
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