Differences between PHP 4 and PHP 5
Differences between PHP 4 & PHP 5
If you are planning on migrating from PHP 4 to PHP 5, here are the main changes you should be aware of.
PHP 5 Object Model
PHP 5 features a greatly improved object model which brings it a lot closer to a fully fledged object orientated programming language. If you have used the PHP 4 object model in any of your applications, here are the major differences between the two.
Assignments and Object Copying
By default, in PHP 4, creating an instance of or assigning a previously instantiated object to a new variable will cause a copy of the object to be created.
PHP Code:
/* PHP 4 */
$object = new MObject; // a copy of the new instance will be assigned to $object
$object2 = $object; // $object will be copied and then assigned to $object2
$object->property = 1; // changes made to $object are not reflected in $object2
As of PHP 5, to give the programmer more flexibility, references are used by default. To obtain a copy of an object in PHP 5, you need to clone it.
PHP Code:
/* php 5 */
$object = new MObject; // a reference will be assigned to $object
$object2 = $object; // assigns the $object reference to $object2
$object->property = 1; // changes made to $object are reflected in $object2
$object3 = clone $object; // $object3 now holds a separate copy of $object
$object3->property = 3; // changes will not be reflected in $object or $object2
Constructors
Constructors in PHP 4 are created in the class template as a method of the same name as the class. As of PHP 5 you should use the __construct(), magic function.
PHP Code:
/* PHP 4 */
class Item
{
/* class constructor */
function Item() {
}
}
class Bin extends Item
{
/* class constructor */
function Bin() {
parent::Item(); // calling the super class constructor
}
}
The same in PHP 5, making it easier to call the super class constructor as you do not need to know its name:
PHP Code:
http://www.php.net/manual/en/language.oop5.typehinting.php
class Item
{
/* class constructor */
function __construct() {
}
}
class Bin extends Item
{
/* class constructor */
function __construct() {
parent::__construct(); // calling the super class constructor
}
}
The new PHP 5 object model has many new features which include:
Databases
The MySql libraries are no longer bundled with PHP 5. If you are compiling from source you will need to have the libraries installed on your system and use the configure option --with-mysql.
If you are installing PHP 5 on windows, you need to ensure that you have MySql installed and edit the php.ini file to enable the php_mysql.dll extension.
PHP 5 also has a new improved MySql extension called MySqli. For those who don't want to install a separate DBMS PHP 5 provides the SqlLite extension.
Other Information
The array_merge() function in PHP 5 now takes only variables of type array as arguments where as in PHP 4 the following code produces this output:
PHP Code:
<?php
/* PHP 4 */
$non_array = 'item4';
$array = Array('item1','item2','item3');
print_r(array_merge($array, $non_array));
?>
Output:
Code:
Array
(
[0] => item1
[1] => item2
[2] => item3
[3] => item4
)
I PHP 5 the same code would produce an error of type E_WARNING and return null. To fix incompatible code you can typcast the variables which may not be arrays:
PHP Code:
// PHP 5
print_r(array_merge((array) $array, (array) $non_array));
A List of backwards incompatible changes between PHP 4 and 5
Information on Moving to PHP 5
PHP 5's new Object Model
