php automatically load objects

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

In PHP 5, this is no longer necessary. You can define an __autoload() function that will be automatically called when trying to use a class that has not yet been defined. By calling this function, the scripting engine has a last chance to load the required classes before PHP fails with an error.

Tip

spl_autoload_register() provides a more flexible way to implement automatic loading of classes. Therefore, use of the __autoload() function is no longer recommended and may be deprecated in a future version.

Note:

Before version 5.3.0, exceptions thrown by the __autoload function cannot be caught by the catch statement block and will result in a fatal error. From 5.3.0+ onwards, exceptions thrown by the __autoload function can be caught by the catch statement block, but they need to follow a condition. If a custom exception is thrown, a corresponding custom exception class must exist. The __autoload function can automatically load custom exception classes recursively.

Note:

Autoloading is not available in PHP’s CLI interactive mode.

Example #1 Automatic loading example

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

function __autoload($class_name){
require_once $class_name.'.php';
}
$obj = new MyClass1();
$obj2 = new MyClass2();

Note: MyClass1.php and MyClass2.php need to be in the same directory as the current script to load. Go to

Example #2 Another example

This example attempts to load the interface ITest:

function __autoload($name) {
   var_dump($name);
}
class Foo implements ITest {
}
/*
string(5) "ITest"
Fatal error: Interface 'ITest' not found in ...
*/

Example #3 Automatically load exception handling in PHP 5.3.0+

This example throws an exception and uses it in the try/catch statement Demonstration in block.

function __autoload($name) {
   echo "Want to load $name.\n";
   throw new Exception("Unable to load $name.");
}
try {
   $obj = new NonLoadableClass();
} catch (Exception $e) {
   echo $e->getMessage(), "\n";
}

The above routine will output:

Want to load NonLoadableClass.
Unable to load NonLoadableClass.

Example #4 Automatic loading exception handling in PHP 5.3.0+ - no custom exception mechanism

This example will An exception was thrown to a custom exception handler that does not exist.

The above routine will output:

Want to load NonLoadableClass.
Want to load MissingException.

Fatal error: Class 'MissingException' not found in testMissingException.php on line 4