Page 251 - Beginning PHP 5.3

Chapter 8: Objects
If the PHP engine can ’ t find an __autoload() function, or if your __autoload() function fails to load
the Person class, the script exits with a “Class ‘ Person ’ not found” error.

Storing Objects as Strings

Objects that you create in PHP are stored as binary data in memory. Although you can pass objects
around using PHP variables, functions, and methods, sometimes its useful to be able to pass objects to
other applications, or via fields in Web forms, for example.

PHP provides two functions to help you with this:
❑ serialize() converts an object — properties, methods, and all — into a string of text

❑ unserialize() takes a string created by serialize() and turns it back into a usable object
The following example shows these two functions in action:

class Person {
public $age;
}

$harry = new Person();
$harry- > age = 28;
$harryString = serialize( $harry );
echo “Harry is now serialized in the following string: ‘$harryString’ < br / > ”;
echo “Converting ‘$harryString’ back to an object... < br / > ”;
$obj = unserialize( $harryString );

echo “Harry’s age is: $obj- > age < br / > ”;
This code creates a simple Person class with one property, $age . It then creates a new Person object,
$harry , and sets its $age property to 28 . It calls serialize() to convert the object to a string, which it
displays. Finally, it converts the string back into a new object, $obj , then displays its $obj - > age

property ( 28 ). Here ’ s the result of running the script:

Harry is now serialized in the following string: ‘O:6:”Person”:1:{s:3:”age”;i
:28;}’
Converting ‘O:6:”Person”:1:{s:3:”age”;i:28;}’ back to an object...
Harry’s age is: 28

You can actually use serialize() and unserialize() on any PHP value, not just objects. However,
it ’ s especially useful with objects and arrays, because these structures can be quite complex and it ’ s not
easy to convert them to strings in any other way.
What ’ s more, when you serialize an object, PHP attempts to call a method with the name __sleep()
inside the object. You can use this method to do anything that ’ s required before the object is serialized.
Similarly, you can create a __wakeup() method that is called when the object is unserialized.

__sleep() is useful for cleaning up an object prior to serializing it, in the same way that you might
clean up in a destructor method. For example, you might need to close database handles, files, and so on.
In addition, __sleep() has another trick up its sleeve. PHP expects your __sleep() method to return

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