PHP class auto-loading mechanism

Auto loading of php:

Before PHP5, if we wanted to use a certain class or class method, it must include or require before it can be used. Every time we use a class, we need to write an include, which is troublesome

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 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 situation: The content in file A.php is as follows

class A{

　public function __construct(){

　　 echo 'fff';

　}

}

?>

The content of the file C.php is as follows:

function __autoload($class)
{
$file = $class . '.php';
if (is_file($file)) {
require_once($file); a = new A(); //__autoload will be automatically called here and the A.php file will be introduced

?>

Second case:

Sometimes I want to customize autoload and give a cooler name for loader, so C.php should be changed to the following:

function loader($class){

$file = $class . '.php';

if (is_file($file)) {
require_once($file);
}
}

spl_autoload_register('loader'); //Register an automatic loading method, overwriting the original __autoload

$a = new A();

?>

The third situation

: I hope to be more advanced and use a class to manage automatic loading

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();

?>

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')); //If it is php5 or above and there is a registration function, register the autoload in the core class you wrote as the automatic loading function

}else{

　function __autoload($class){ //If not, rewrite the PHP native function __autoload function and let it call its own core function.

　　return core::autoload($class);

　}

}

It’s great to put this paragraph at the front of the entry file~

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