PHP class automatic loading mechanism and PHP class loading mechanism

PHP class automatic loading mechanism and PHP class loading mechanism

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:

<? Php

Class {

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 to introduce the. php file.

?>

Case 2:Sometimes I want to customize autoload and a cooler name loader, 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 '); // register an automatic loading method to overwrite the original _ autoload

$ A = new ();

?>

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 ();

?>

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 php5 and above exist, register autoload in the Self-written core class as the auto-loaded function.

} Else {

Function _ autoload ($ class) {// if not, rewrite the native php function _ autoload to allow it to call its core function.

Return core: autoload ($ class );

}

}

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

Reprinted: http://www.cnblogs.com/zhongyuan/p/3583201.html