what is php autoload class

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 &#39;fff&#39;;
　　}
}
?>

The content of file C.php is as follows :

<?php   
function autoload($class)   
{   
$file = $class . &#39;.php&#39;;   
if (is_file($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 = $class . &#39;.php&#39;;
if (is_file($file)) {
require_once($file);
}
}
spl_autoload_register(&#39;loader&#39;); //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 = $class . &#39;.php&#39;;   
if (is_file($file)) {   
require_once($file);   
}   
}   
} 
spl_autoload_register(array(&#39;Loader&#39;, &#39;loadClass&#39;));   

$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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