What is autoloading classes in PHP ?

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In order to use a class defined in another PHP script, we can incorporate it with include or require statements. However, PHP’s autoloading feature does not need such explicit inclusion. Instead, when a class is used (for declaring its object etc.) PHP parser loads it automatically, if it is registered with spl_autoload_register() function. Any number of classes can thus be registered. This way PHP parser gets a last chance to load the class/interface before emitting an error.

Syntax:

PHP

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

Note: The class will be loaded from its corresponding “.php” file when it comes into use for the first time.

Autoloading:

Example 1: This example shows how a class is registered for autoloading.

PHP

<?php 
    spl_autoload_register(function ($class_name) { 
       include $class_name . '.php'; 
    }); 
    $obj = new test1(); 
    $obj2 = new test2(); 
    echo "objects of test1 and test2 class created successfully"; 
?>

Output:

objects of test1 and test2 class created successfully

Note: If the corresponding “.php” file having class definition is not found, the following error will be displayed.

Output:

Warning: include(test1.php): failed to open stream:

No such file or directory in /home/guest/sandbox/5efa1ebc-c366-4134-8ca9-9028c8308c9b.php on line 3

Warning: include(): Failed opening ‘test1.php’ for inclusion (include_path=’.:/usr/local/lib/php’)

in /home/guest/sandbox/5efa1ebc-c366-4134-8ca9-9028c8308c9b.php on line 3

Fatal error: Uncaught Error: Class ‘test1’ not found in

/home/guest/sandbox/5efa1ebc-c366-4134-8ca9-9028c8308c9b.php:5

Stack trace:

#0 {main}

thrown in /home/guest/sandbox/5efa1ebc-c366-4134-8ca9-9028c8308c9b.php on line 5

Autoloading with exception handling

Example 2:

PHP

<?php 
    spl_autoload_register(function($className) { 
       $file = $className . '.php'; 
       if (file_exists($file)) { 
          echo "$file included\n"; 
          include $file; 
       }  
      else { 
          throw new Exception("Unable to load $className."); 
       } 
    }); 
    try { 
       $obj1 = new test1(); 
       $obj2 = new test10(); 
    }  
    catch (Exception $e) { 
       echo $e->getMessage(), "\n"; 
    } 
?>