PHP Autoloading Classes

How to autoload a class

To develop a large scale application, which should be fully based on object-oriented. This application executes a single file, and this single creates instances & call objects of all stored object-orient program files.

So, there are needs a mechanism to call classes automatically.

The __autoload() function is used to autoload classes and interfaces, It have alternate function to autoload classes is “spl_autoload_register()”.

it's preferred to use the spl_autoload_register() function. This is because it is a more flexible alternative (enabling for any number of autoloaders to be specified in the application, such as in third-party libraries). For this reason, using __autoload() is discouraged and it may be deprecated in the future.

Note:

Prior to PHP 5.3, exceptions thrown in the __autoload() function could not be caught in the catch block and would result in a fatal error. From PHP 5.3 and upwards, this is possible provided that if a custom exception is thrown, then the custom exception class is available. The __autoload() function may be used recursively to autoload the custom exception class.
 

Note:

Autoloading is not available if using PHP in CLI interactive mode.
 

Note:

If the class name is used e.g. in call_user_func() then it can contain some dangerous characters such as ../. It is recommended to not use the user-input in such functions or at least verify the input in __autoload().
 

How to autoload a class with an example

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

<?php

spl_autoload_register(function ($class_name) {
    include $class_name . '.php';
});

$obj  = new MyClass1();
$obj2 = new MyClass2();

?>

How to autoload a class with an exception handler

This example throws an exception and demonstrates the try/catch block.

<?php

spl_autoload_register(function ($name) {
    echo "Want to load $name.\n";
    throw new Exception("Unable to load $name.pa");
});

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}

?>

Output: