An in-depth understanding of the automatic loading mechanism of PHP classes _php instance

Automatic loading of PHP:

Before PHP5, we have to use a class or class method, which must include or require, and then use, each time with a class, need to write an include, trouble

PHP authors want to be simple, it is best to reference a class, if the current does not include in, the system can automatically find the class, automatic introduction ~

So: the __autoload () function came into being.

It is usually placed inside the application entry class, such as Discuz, in the class_core.php.

Let's start with the plain examples:

In the first case : The contents of the document a.php are as follows

<?php

class a{public

function __construct () {    echo ' FFF ';

}

}

?>　　

The contents of the file c.php are as follows:

<?php  
function __autoload ($class)  
{  
$file = $class. '. php ';  
if (Is_file ($file)) {  
require_once ($file);  
}  
}  
$a = new A (); This will automatically invoke __autoload and introduce a.php files

?>

The second scenario: Sometimes I want to be able to customize AutoLoad and want to play a cooler name loader, then c.php to read as follows:

<?php
function Loader ($class)
{
$file = $class. '. php ';
if (Is_file ($file)) {
require_once ($file);
}
}

Spl_autoload_register (' loader '); Registers an automatic loading method, overwriting the original __autoload

$a = new A ();

>

A third case : I want to be tall, with 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 ();

? >

Current is the best form.

Usually we place the spl_autoload_register (*) in the entry script, which is quoted at the outset. For example, the following discuz approach.

if (function_exist (' Spl_autoload_register ')) {

spl_autoload_register (array (' core ', ' autoload '));//If it is php5 above, There is a registration function, then register the AutoLoad in the core class that you write to automatically load functions

}else{function

__autoload ($class) {     //if not, rewrite PHP native function __ AutoLoad function to call its own core middle function.　　Return

core::autoload ($class);

}

}

This paragraph is thrown at the front of the entry file, which is naturally very good.

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