As you’ve seen, PHP ships with numerous extension libraries that combine useful functionality into distinct packages that you can access from your scripts. We covered using the gd, fpdf, and libxslt extension libraries in Chapters 9, 10, and 11.
In addition to using the extensions that ship with PHP, you
can create libraries of your own code that you can use in more than one
part of your website. The general technique is to store a collection of
related functions in a PHP file. Then, when you need to use that functionality in a page, you can
require_once() to insert the
contents of the file into your current script.
Note that there are three other inclusion type functions that
can also be employed. They are
include(). Chapter 2
discusses these functions in detail.
For example, say you have a collection of functions that help create
HTML form elements in valid HTML: one
function in your collection creates a text field or a
area (depending on
how many characters you tell it the maximum is), another creates
a series of pop-ups from which to set a date
and time, and so on. Rather than copying the code into many
pages, which is tedious, error-prone, and makes it difficult to fix any
bugs found in the functions, creating a function library is the sensible
When you are combining functions into a code library, you should be careful to maintain a balance between grouping related functions and including functions that are not often ...