Migrating from PHP 4 to PHP 5.0.x 

What has changed in PHP 5.0.x ¶

PHP 5 and the integrated Zend Engine 2 have greatly improved PHP’s performance and capabilities, but great care has been taken to break as little existing code as possible. So migrating your code from PHP 4 to 5 should be very easy. Most existing PHP 4 code should be ready to run without changes, but you should still know about the few differences and take care to test your code before switching versions in production environments.
CLI and CGI ¶
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.

Migrating Configuration Files ¶

Since the ISAPI modules changed their names, from php4xxx to php5xxx, you need to make some changes in the configuration files. There were also changes in the CLI and CGI filenames. Please refer to the corresponding section for more information.
Migrating the Apache configuration is extremely easy. See the example below to check the change you need to do:
Example #1 Migrating Apache configuration files for PHP 5
# change this line:    LoadModule php4_module /php/sapi/php4apache2.dll # with this one:LoadModule php5_module /php/php5apache2.dll
If your web server is running PHP in CGI mode, you should note that the CGI version has changed its name from php.exe to php-cgi.exe. In Apache, you should do something like this:
Example #2 Migrating Apache configuration files for PHP 5, CGI mode
# change this line:    Action application/x-httpd-php “/php/php.exe”  # with this one:Action application/x-httpd-php “/php/php-cgi.exe”
In other web servers you need to change either the CGI or the ISAPI module filenames.
Databases ¶
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 and maintenance problems. MySQL is supported with the only change being that MySQL support is no longer enabled by default in PHP 5. This essentially means that PHP doesn’t include the –with-mysql option in the configure line so that you must now manually do this when compiling PHP. Windows users will need to edit php.ini and enable the php_mysql.dll DLL as in PHP 4 no such DLL existed, it was simply built into your Windows PHP binaries.
 
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.