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.