PHP and MySQL for Dynamic Web Sites: Visual Quickpro Guide, Second Edition

Validating Data by Type

For the most part, the form validation I’ve demonstrated has been rather minimal, often just checking if a variable has any value at all. In many situations, this really is the best you can do. For example, there’s no clear pattern for what a valid street address is or what a user might enter into a comments field. Still, much of the data you’ll work with can be validated in stricter ways. Later in the chapter, the sophisticated concept of regular expressions will demonstrate just that. But here I’ll cover the more approachable ways you can validate some data by type.

PHP supports many types of data: strings, numbers (integers and floats), arrays, and so on. For each of these, there’s a specific function that checks if ...