Chapter 1. Introduction

PHP 4 is a wildly popular web programming language. Web servers on over 15,000,000 domains support PHP. PHP is the most popular Apache module by almost a 2-to-1 margin. But if PHP's so great, why do we need PHP 5?

Well, PHP 4 isn't perfect. While it makes developing web applications quick and easy, it's occasionally weighted down by its legacy baggage. This makes tackling some problems unnecessarily difficult.

In particular, PHP's version of object-oriented programming (OOP) lacks many features, the MySQL extension doesn't support the new MySQL 4.1 client protocol, and XML support is a hodgepodge.

Fortunately, PHP 5 improves on PHP 4 in three major areas:

• Object-oriented programming

• MySQL

• XML

These items have all been completely rewritten, turning them from limitations into star attractions. While these changes alone warrant a new version of PHP, PHP 5 also provides:

• SQLite for an embedded database

• Iterators

• Error handling using exceptions

• Streams

• SOAP

Some of these features, such as iterators and exceptions, are available only due to fundamental changes in PHP's core . Others, such as streams and SQLite, are PHP 4.3 features that have matured into prime-time use in PHP 5.

This book shows you how to take advantage of these new features in your applications. Additionally, it places a special emphasis on not just telling you what's new, but showing you how and why it's new.

Whenever possible, there's a direct comparison between the PHP 4 method of solving a task and the PHP 5 solution. The PHP 5 way is frequently shorter, more elegant, and provides you with greater flexibility. The before-and-after examples demonstrate in clear code what's better about PHP 5 and provide you with concrete examples to ease the transition from PHP 4 to PHP 5.

This chapter serves as a dual introduction to both PHP 5 and Upgrading to PHP 5 . It begins with a brief history of PHP that provides the motivation behind PHP 5. The next section provides a short description of all the major new features of PHP 5 and, at the same time, explains how the book is organized. This chapter ends with a discussion of how to install and configure PHP 5.