In-depth understanding of the automatic loading mechanism of PHP classes and deep understanding of php Loading

In-depth understanding of the automatic loading mechanism of PHP classes and deep understanding of php Loading

Php automatic loading:

Before php5, we need to use a class or class method, which must be included or require before it can be used. Every time we use a class, we need to write an include statement, which is troublesome.

The php author wants to make it simple. It is best to reference a class. If no include is included, the system can automatically find the class and introduce it automatically ~

So the :__ autoload () function came into being.

It is usually placed in the application entry class, such as discuz, and in class_core.php.

Let's give a simple example:

First case: The content in file A. php is as follows:

<?phpclass A{　　public function __construct(){　　    echo 'fff';　　}}?>

The content in file C. php is as follows:

<? Php function _ autoload ($ class) {$ file = $ class. '. php '; if (is_file ($ file) {require_once ($ file) ;}}$ a = new A (); // This will automatically call _ autoload, introduce. PHP file?>

Case 2:Sometimes I want to customize autoload and a cooler name loader, C. php is changed to the following:

<? Phpfunction loader ($ class) {$ file = $ class. '. php '; if (is_file ($ file) {require_once ($ file) ;}} spl_autoload_register ('loader'); // register an automatic loading method, overwrite the original _ autoload $ a = new A ();?>

Case 3: I want to 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();?>

The current format is the best.

Generally, we place spl_autoload_register (*) In the portal script, which is referenced from the beginning. For example, the following discuz practice.

If (function_exist ('spl _ autoload_register ') {spl_autoload_register (array ('core', 'autoload'); // if it is php5 or above, a registration function exists, then, register the autoload function in the core class you wrote as the automatic loading function} else {function _ autoload ($ class) {// if not, rewrite the php native function _ autoload function, let it call functions in its core. Return core: autoload ($ class );}}

This part is thrown at the beginning of the entrance file, which is naturally excellent ~

The above in-depth understanding of the automatic loading mechanism of PHP class is all the content shared by the editor. I hope to give you a reference and support for the help house.