Part 4 of the PHP’s Source Code for PHP Developers series is up over on Nikic’s Blog. In it, he discusses how arrays are handled in PHP internals. He talks a lot about hash tables and symbol tables, and how they work together to make PHP a working language. Part 5 will be back over here, and we’ll talk about objects and classes! Enjoy!

In this third post of the PHP's Source Code for PHP Developers series, we’re going to expand on the prior posts to help understand how PHP works internally. In the first post of the series, we looked at how to view PHP’s source code, how it’s structured as well as some basic C pointers for PHP developers. The second post introduced functions into the mix. This time around, we’re going to dive into one of the most useful structures in PHP: variables.

Part 2 of the PHP’s Source Code for PHP Developers series is up over on Nikic’s Blog. In it, he discusses how internal PHP functions are defined, and how to figure out what they do. Part 3 will be back over here and will cover how variables work internally (The ZVAL). Enjoy!

As a PHP developer, I find myself referencing PHP’s source code more and more in my normal everyday work. It’s been very useful in everything from understanding what’s happening behind the scenes to figuring out weird edge-cases to see why something that should be working isn’t. And it’s also very useful in the cases when the documentation is either missing, incomplete or wrong. So, I’ve decided to share what I’ve learned in a series of posts designed to give PHP developers enough knowledge to actually read the C source code behind PHP. No prior knowledge of C should be necessary (we’ll cover some of the basics), but it will help.

This is the first post of the series. In this post, we’ll walk through the basics of the PHP application: where to find it, the general structure of the codebase and a few really fundamental concepts about the C language. To be clear, the goal of the series is to get a reading comprehension of the source code. So that means that at some points in the series, some simplifications will be made to concepts to get the point across without over-complicating things. It won’t make a significant difference for reading, but if you’re trying to write for the core, there is more that will be needed. I’ll try to point out these simplifications when I make them…

Additionally, this series is going to be based off the 5.4 codebase. The concepts should be pretty much the same from version to version, but this way there’s a defined version that we’re working against (to make it easier to follow later, when new versions come out).

So let’s kick it off, shall we?