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Hi, I 'm Aditya, the guy behind this website and many other. This site acts as my web playground, where I share all about me, my work and my knowledge.

I have over 8 yrs hands on experience in PHP, Mysql, JavaScript, open sources CMS like Joomla, Wordpress etc. During these 8 years, I have worked on more than 200 projects and/or websites but could not spare time for my blog.

 

 

Difference between Php4 and Php5

Backward Incompatible Changes

Although most existing PHP 4 code should work without changes, you should pay attention to the following backward incompatible changes:

  • There are some new reserved keywords.
  • strrpos() and strripos() now use the entire string as a needle.
  • Illegal use of string offsets causes E_ERROR instead of E_WARNING. An example illegal use is: $str = 'abc'; unset($str[0]);.
  • array_merge() was changed to accept only arrays. If a non-array variable is passed, a E_WARNING will be thrown for every such parameter. Be careful because your code may start emitting E_WARNING out of the blue.
  • PATH_TRANSLATED server variable is no longer set implicitly under Apache2 SAPI in contrast to the situation in PHP 4, where it is set to the same value as the SCRIPT_FILENAME server variable when it is not populated by Apache. This change was made to comply with the » CGI specification. see also the $_SERVER['PATH_TRANSLATED'] description in the manual. This issue also affects PHP versions >= 4.3.2.
  • The T_ML_COMMENT constant is no longer defined by the Tokenizer extension. If error_reporting is set to E_ALL, PHP will generate a notice. Although the T_ML_COMMENT was never used at all, it was defined in PHP 4. In both PHP 4 and PHP 5 // and /* */ are resolved as the T_COMMENT constant. However the PHPDoc style comments /** */, which starting PHP 5 are parsed by PHP, are recognized as T_DOC_COMMENT.
  • $_SERVER should be populated with argc and argv if variables_order includes "S". If you have specifically configured your system to not create $_SERVER, then of course it shouldn't be there. The change was to always make argc and argv available in the CLI version regardless of the variables_order setting. As in, the CLI version will now always populate the global $argc and $argv variables.
  • An object with no properties is no longer considered "empty".
  • In some cases classes must be declared before use. It only happens if some of the new features of PHP 5 (such as interfaces) are used. Otherwise the behaviour is the old.
  • get_class(), get_parent_class() and get_class_methods() now return the name of the classes/methods as they were declared (case-sensitive) which may lead to problems in older scripts that rely on the previous behaviour (the class/method name was always returned lowercased). A possible solution is to search for those functions in all your scripts and use strtolower(). This case sensitivity change also applies to the magical predefined constants __CLASS__, __METHOD__, and __FUNCTION__. The values are returned exactly as they're declared (case-sensitive).
  • ip2long() now returns FALSE when an invalid IP address is passed as argument to the function, and no longer -1.
  • If there are functions defined in the included file, they can be used in the main file independent if they are before return() or after. If the file is included twice, PHP 5 issues fatal error because functions were already declared, while PHP 4 doesn't complain about it. It is recommended to use include_once() instead of checking if the file was already included and conditionally return inside the included file.
  • include_once() and require_once() first normalize the path of included file on Windows so that including A.php and a.php include the file just once.
  • Passing an array to a function by value no longer resets the array's internal pointer for array accesses made within the function. In other words, in PHP 4 when you passed an array to a function, its internal pointer inside the function would be reset, while in PHP 5, when you pass an array to a function, its array pointer within the function will be wherever it was when the array was passed to the function.

New Functions

In PHP 5 there are some new functions. Here is the list of them:

Arrays:

  • array_combine() – Creates an array by using one array for keys and another for its values
  • array_diff_uassoc() – Computes the difference of arrays with additional index check which is performed by a user supplied callback function
  • array_udiff() – Computes the difference of arrays by using a callback function for data comparison
  • array_udiff_assoc() – Computes the difference of arrays with additional index check. The data is compared by using a callback function
  • array_udiff_uassoc() – Computes the difference of arrays with additional index check. The data is compared by using a callback function. The index check is done by a callback function also
  • array_walk_recursive() – Apply a user function recursively to every member of an array
  • array_uintersect_assoc() – Computes the intersection of arrays with additional index check. The data is compared by using a callback function
  • array_uintersect_uassoc() – Computes the intersection of arrays with additional index check. Both the data and the indexes are compared by using separate callback functions
  • array_uintersect() – Computes the intersection of arrays. The data is compared by using a callback function

InterBase:

iconv:

Streams:

Date and time related:

Strings:

  • str_split() – Convert a string to an array
  • strpbrk() – Search a string for any of a set of characters
  • substr_compare() – Binary safe optionally case insensitive comparison of two strings from an offset, up to length characters

Other:

New Object Model

In PHP 5 there is a new Object Model. PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).

Many PHP programmers aren't even aware of the copying quirks of the old object model and, therefore, the majority of PHP applications will work out of the box, or with very few modifications.

The new Object Model is documented at the Language Reference.

In PHP 5, function with the name of a class is called as a constructor only if defined in the same class. In PHP 4, it is called also if defined in the parent class.

See also the zend.ze1_compatibility_mode directive for compatability with PHP 4.

Passed by Reference
This is an important change. In PHP4, everything was passed by value, including objects. This has changed in PHP5 — all objects are now passed by reference.

PHP Code:
$joe = new Person();
$joe->sex = 'male';

$betty = $joe;
$betty->sex = 'female';

echo $joe->sex; // Will be 'female'
The above code fragment was common in PHP4. If you needed to duplicate an object, you simply copied it by assigning it to another variable. But in PHP5 you must use the new clone keyword.

Note that this also means you can stop using the reference operator (&). It was common practice to pass your objects around using the & operator to get around the annoying pass-by-value functionality in PHP4.

Class Constants and Static Methods/Properties
You can now create class constants that act much the same was as define()'ed constants, but are contained within a class definition and accessed with the :: operator.

Static methods and properties are also available. When you declare a class member as static, then it makes that member accessible (through the :: operator) without an instance. (Note this means within methods, the $this variable is not available)

Visibility
Class methods and properties now have visibility. PHP has 3 levels of visibility:

   1. Public is the most visible, making methods accessible to everyone and properties readable and writable by everyone.
   2. Protected makes members accessible to the class itself and any subclasses as well as any parent classes.
   3. Private makes members only available to the class itself.

Unified Constructors and Destructors
PHP5 introduces a new unified constructor/destructor names. In PHP4, a constructor was simply a method that had the same name as the class itself. This caused some headaches since if you changed the name of the class, you would have to go through and change every occurrence of that name.

In PHP5, all constructors are named __construct(). That is, the word construct prefixed by two underscores. Other then this name change, a constructor works the same way.

Also, the newly added __destruct() (destruct prefixed by two underscores) allows you to write code that will be executed when the object is destroyed.

Abstract Classes
PHP5 lets you declare a class as abstract. An abstract class cannot itself be instantiated, it is purely used to define a model where other classes extend. You must declare a class abstract if it contains any abstract methods. Any methods marked as abstract must be defined within any classes that extend the class. Note that you can also include full method definitions within an abstract class along with any abstract methods.

Interfaces
PHP5 introduces interfaces to help you design common APIs. An interface defines the methods a class must implement. Note that all the methods defined in an interface must be public. An interface is not designed as a blueprint for classes, but just a way to standardize a common API.

The one big advantage to using interfaces is that a class can implement any number of them. You can still only extend on parent class, but you can implement an unlimited number of interfaces.

Magic Methods
There are a number of "magic methods" that add an assortment to functionality to your classes. Note that PHP reserves the naming of methods prefixed with a double-underscore. Never name any of your methods with this naming scheme!

Some magic methods to take note of are __call, __get, __set and __toString. These are the ones I find most useful.

Finality
You can now use the final keyword to indicate that a method cannot be overridden by a child. You can also declare an entire class as final which prevents it from having any children at all.

Error Reporting

As of PHP 5 the error reporting constant E_STRICT is available, with the value 2048. When enabled, messages will be issued to warn you about code usage which is deprecated or which may not be future-proof.

Exceptions

PHP finally introduces exceptions! An exception is basically an error. By using an exception however, you gain more control the simple trigger_error notices we were stuck with before.

An exception is just an object. When an error occurs, you throw an exception. When an exception is thrown, the rest of the PHP code following will not be executed. When you are about to perform something "risky", surround your code with a try block. If an exception is thrown, then your following catch block is there to intercept the error and handle it accordingly. If there is no catch block, a fatal error occurs.

PHP Code:
try {
    $cache->write();
} catch (AccessDeniedException $e) {
    die('Could not write the cache, access denied.');
} catch (Exception $e) {
   die('An unknown error occurred: ' . $e->getMessage());

 

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