How backwards compatible is php 5 with php 4?

Question

I work on a code base written in php 4. I'd like to go through the process of upgrading the code to php 5 (the latest version my host provides). I'm wondering if anyone else has gone through a similar upgrade experience and can share what gotchas/pitfalls there are, what has to change in my code, what is not backwards compatible between the two versions?

Answer 1

Take a look at the guide for migrating from PHP 4 to 5. Your existing PHP 4 code should mostly still work, though there are some backward-incompatible changes.