PHP 4 and 5 differences

Posted on: December 25, 2008

At first I would like to thank for their clear and cool documentation. Recently I’ve gone through the differences in between php4 and php5. I’ve found some interesting things by studying this topic. I think you all should have a look if you want to be a good developer. If you want a better performance and more features in your application easily then this post is appropriate for you. Happy Christmas!!

Type Hinting
PHP 5 introduces Type Hinting. Functions are now able to force parameters to be objects (by specifying the name of the class in the function prototype) or arrays (since PHP 5.1). However, if NULL is used as the default parameter value, it will be allowed as an argument for any later call.

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.

List of new Keywords
These words have special meaning in PHP. Some of them represent things which look like functions, some look like constants, and so on–but they’re not, really: they are language constructs. You cannot use any of the following words as constants, class names, function or method names. Using them as variable names is generally OK, but could lead to confusion.You will find detailed documentation on these new keywords by clicking on it.

abstract catch clone final implements interface instanceof namespace private protected public throw try


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. Please refer to » bug #23610 for further information, and 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.

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


  • 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




Date and time related:


  • 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


New Directives
There were some new php.ini directives introduced in PHP 5. Here is a list of them:

  • mail.force_extra_parameters – Force the addition of the specified parameters to be passed as extra parameters to the sendmail binary. These parameters will always replace the value of the 5th parameter to mail(), even in safe mode
  • register_long_arrays – allow/disallow PHP to register the deprecated long $HTTP_*_VARS
  • session.hash_function – select a hash function (MD5 or SHA-1)
  • session.hash_bits_per_character – define how many bits are stored in each character when converting the binary hash data to something readable (from 4 to 6)
  • zend.ze1_compatibility_mode – Enable compatibility mode with Zend Engine 1 (PHP 4)

Magic Methods
The function names __construct, __destruct, __call, __callStatic, __get, __set, __isset, __unset, __sleep, __wakeup, __toString, __set_state and __clone are magical in PHP classes. You cannot have functions with these names in any of your classes unless you want the magic functionality associated with them.

In PHP 5 there were some changes in CLI and CGI filenames. In PHP 5, the CGI version was renamed to php-cgi.exe (previously php.exe) and the CLI version now sits in the main directory (previously cli/php.exe).
In PHP 5 it was also introduced a new mode: php-win.exe. This is equal to the CLI version, except that php-win doesn’t output anything and thus provides no console (no “dos box” appears on the screen). This behavior is similar to php-gtk.
In PHP 5, the CLI version will always populate the global $argv and $argc variables regardless of any php.ini directive setting. Even having register_argc_argv set to off will have no affect in CLI.

Error Reporting
As of PHP 5 new error reporting constant E_STRICT was introduced with value 2048. It enables run-time PHP suggestions on your code interoperability and forward compatibility, that will help you to keep latest and greatest suggested method of coding. E.g. STRICT message will warn you on using deprecated functions.
Note: E_ALL does not include E_STRICT so it’s not enabled by default

There were some changes in PHP 5 regarding databases (MySQL and SQLite).
In PHP 5 the MySQL client libraries are not bundled, because of license problems and some others. For more information, read the FAQ entry.
There is also a new extension, MySQLi (Improved MySQL), which is designed to work with MySQL 4.1 and above.
Since PHP 5, the SQLite extension is built-in PHP. SQLite is an embeddable SQL database engine and is not a client library used to connect to a big database server (like MySQL or PostgreSQL). The SQLite library reads and writes directly to and from the database files on disk.


7 Responses to "PHP 4 and 5 differences"

Good post 🙂

Awasome . Nice post specially for me. We want more and more tips.. form your Blog.

Great sir 🙂 this is the best answer for differentiating between PHP4 and PHP5.

Nice post go on.

Cool post… In few words, its great 🙂

Как всегда на высоте.

Как всегда на высоте (постоянный читатель 🙂 )

Ну ты даёшь!

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I am Nurul Ferdous a Zend Certified Engineer (ZCE), serving at Bangladesh Internet Press Limited (BIPL) as programmer. I am a FOSS advocate and love RnD.


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