Definitely, one of the most common tasks that PHP programmers have to tackle during the development of web applications is validating user-supplied data. This fact brings up a crucial and mandatory rule: the client side is always non-trusted terrain with little or no control. Consequently, any data coming from it needs to be properly filtered and thoroughly checked before doing something useful with it.

Fortunately, the introspective capabilities offered by PHP allow you to check incoming data in a pretty straightforward way. It comes packaged with a number of native functions, which you’ve surely used hundreds of times before, that permit you to verify different data types very easily. These data types include strings and float numbers, integers, arrays and objects. This neat set of functions, along with some extra features bundled exclusively with PHP 5, such as type hinting, allow developers build libraries that can be used for checking empty strings and numeric ranges, email addresses and URLs, and so forth.

Purely aside from these other developer-built libraries, however, PHP 5 also includes by default a useful library that allows you to perform all of these types of validation tasks by means of a bunch of native filters. Yes, these rather overlooked filters will let you check for integers and float numbers, URLs, email addresses, etc., even more easily than by using your own custom functions. Best of all, they don’t require any additional configuration.

Indeed, the use of native PHP filters may contribute significantly to saving time and effort when it comes to validating input data. In this series of articles I’m going to attempt to provide you with a concise guide to how to use them, as usual by way of a decent variety of code samples.

So, now that that you know what to expect from this group of articles, it’s time to move forward and start discovering the real power that stands behind using filters in PHP 5. Let’s begin now!