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By now, you should have a solid understanding of the details of the PHP language and its use in a variety of common situations. Now we're going to show you some techniques that you may find useful in your PHP applications, such as code libraries, templating systems, efficient output handling, error handling, and performance tuning.
As you've seen, PHP ships with numerous extension libraries that combine useful functionality into distinct packages that you can access from your scripts. In previous chapters, we've covered using the GD, pdflib, and Sablotron extension libraries, and Appendix B lists 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 a .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.
For example, say you have a collection of functions that help create HTML form elements in valid HTML—one function 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 into a code library, you should be careful to maintain a balance between grouping related functions and including functions that are not often used. When you include a code library in a page, all of the functions in that library are parsed, whether you use them all or not. PHP's parser is quick, but not parsing a function is even faster. At the same time, you don't want to split your functions over too many libraries, so that you have to include lots of files in each page, because file access is slow.
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| 12.8. Security Redux |  | 13.2. Templating Systems |
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