Appendix B. Migrating from PHP 4 to PHP 5

Table of Contents
What has changed in PHP 5
Backward Incompatible Changes
CLI and CGI
Migrating Configuration Files
New Functions
New Directives
Databases
New Object Model
Error Reporting

What has changed in PHP 5

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.