Before I start explaining how to use filters in PHP 5, it’s convenient to check which of them comes with the PHP distribution. To do this, I’m going to use a pair of handy native functions called “filter_list()” and “filter_id()." The first one will return an array of the existing filters and the second one will retrieve their corresponding IDs.

A simple demonstration of how to use these functions is coded below. Take a look at the following example:

<?php

// example on using the 'filter_list()' function

foreach(filter_list() as $id => $filter)

{

echo '<p> Filter Name: ' . $filter . ' ------------- Filter ID: ' . filter_id($filter) . '</p><hr />';

}

/* displays the following

Filter Name: int ------------- Filter ID: 257

Filter Name: boolean ------------- Filter ID: 258

Filter Name: float ------------- Filter ID: 259

Filter Name: validate_regexp ------------- Filter ID: 272

Filter Name: validate_url ------------- Filter ID: 273

Filter Name: validate_email ------------- Filter ID: 274

Filter Name: validate_ip ------------- Filter ID: 275

Filter Name: string ------------- Filter ID: 513

Filter Name: stripped ------------- Filter ID: 513

Filter Name: encoded ------------- Filter ID: 514

Filter Name: special_chars ------------- Filter ID: 515

Filter Name: unsafe_raw ------------- Filter ID: 516

Filter Name: email ------------- Filter ID: 517

Filter Name: url ------------- Filter ID: 518

Filter Name: number_int ------------- Filter ID: 519

Filter Name: number_float ------------- Filter ID: 520

Filter Name: magic_quotes ------------- Filter ID: 521

Filter Name: callback ------------- Filter ID: 1024

*/

?>

As you can see in the above code sample, the combined use of the “filter_list()” and “filter_id()” functions provides useful information about the filters that are available with the PHP 5 distribution. In this particular case, the name and ID of each filter is displayed on screen via a simple “foreach” construct, which helps you understand each one's functionality. 

Of course, from the previous example it’s easy to see that there are filters available for checking integers and float numbers, Boolean values and regular expressions, URLs, email and IP addresses, strings and special characters, and so forth. However, since this will be a progressive process, I’m going to discuss  each filter in detail in successive tutorials of this series.

At this point you should have some idea of how useful PHP 5 filters can really be for validating incoming data. Therefore, it’s time to start an in-depth discussion of the first filter shown by the previous list. It is the one responsible for checking whether a given value is an integer.

This brand new PHP 5 filter will be explored in detail in the next segment. Thus, to learn how to work with it, click on the link below and read the next few lines.