PHP automatic loading class __autoload() function_PHP tutorial

php automatically loads classes __autoload() function

When many developers write object-oriented applications, they create a PHP source file for the definition of each class. A big annoyance is having to write a long list of include files at the beginning of each script (one file per class).

In a software development system, it is impossible to write all classes in a PHP file. When a class declared in another file needs to be called in a PHP file, the file needs to be introduced through include. However, sometimes, in projects with many files, it is a headache to include all the files of the required classes one by one. So, can we include this class when it is used? Where to import the php file? This is what we are going to talk about here Auto-loading class.

In PHP 5, you can define an __autoload() function, which will be automatically called when trying to use a class that has not yet been defined. By calling this function, the script engine has the last chance to load what is needed before PHP fails with an error. class, one parameter received by the __autoload() function is the class name of the class you want to load, so when you are working on a project, you need to follow certain rules when organizing the file names of the defined classes. It is best to center on the class name. , you can also add a unified prefix or suffix to form the file name, such as xxx_classname.php, classname_xxx.php and classname.php, etc.

This example attempts to load the MyClass1 and MyClass2 classes from the MyClass1.php and MyClass2.php files respectively

<?php
function __autoload($classname)
{
	require_once $classname . '.php';
}

//MyClass1类不存在时，自动调用__autoload()函数，传入参数”MyClass1”
$obj = new MyClass1();

//MyClass2类不存在时，自动调用__autoload()函数，传入参数”MyClass2”
$obj2 = new MyClass2();
?>

The processing method of DiscuzX2.5 is:

<?php
if (function_exists('spl_autoload_register'))
{
	spl_autoload_register(array('core', 'autoload'));
}
else
{
	function __autoload($class)
	{
		return core::autoload($class);
	}
}

Note: __autoload() is specially designed for classes that do not exist! ! ! Many frameworks use this function to implement automatic loading of class files ! ! !

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