3.5. Built-In Functions Versus UDFs

So far you have been introduced to functions that you create yourself by writing code specifically for a defined custom purpose. These are called user-defined functions or UDFs. Additionally, PHP includes a plethora of predefined functions that you can use within your applications. There are functions for string manipulation, array management, database connectivity, date and time information, and so on. Be sure to check your PHP resources before you create functions that may already exist. Also, keep in mind that these native, or built-in, functions are always faster than ones you may build yourself, because they are highly optimized for use within PHP. Be aware, however, that some of these functions are very specific and therefore require dependent libraries to be added to the core of PHP. For MySQL database interaction, for example, you must add the MySQL library to the PHP environment before it will work at all.