How to load classes in PHP ?

PHP load classes are used for declaring its object etc. in object oriented applications. PHP parser loads it automatically, if it is registered with spl_autoload_register() function. PHP parser gets the least chance to load class/interface before emitting an error.

Syntax:

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

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

Autoloading

Example:

PHP

<?php
    spl_autoload_register(function ($class_name) {
        include $class_name . '.php';
    });
    $obj = new mytest1();
    $obj2 = new mytest2();
    echo "Objects of mytest1 and mytest2 "
        + "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.

Warning: include(): Failed opening 'test10.php' for 
inclusion (include_path='C:\xampp\php\PEAR') in line 4
PHP Fatal error: Uncaught Error: Class 'test10' not found.

Autoloading with exception handling

Example:

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";
    }
?>

Output:

Unable to load test1.