Programming PHP, 2nd Edition

Code Libraries

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 9-11, and Appendix B lists a vast array of almost all of the available extensions.

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 web site. The general technique is to store a collection of related functions in a file, typically with an .inc file extension. Then, when you need to use that functionality in a page, you can use require_once( ) to insert the contents of the file into your current script.

Tip

Note that there are three other inclusion type functions that can also be employed. They are require( ), include_once( ), and include( ). Look up the idiosyncrasies of these functions and use them to their most beneficial.

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 textarea (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 choice.

When you are combining functions ...