As you progress in your use of PHP programming, you are likely to start building a library of functions that you think you will need again. You’ll also probably start using libraries created by other programmers.
There’s no need to copy and paste these functions into your code.
You can save them in separate files and use commands to pull them in.
There are two types of commands to perform this action:
include, you can tell PHP
to fetch a particular file and load all its contents. It’s as if you
pasted the included file into the current file at the insertion point.
Example 5-6 shows how you would include a
file called library.php.
<?php include "library.php"; // Your code goes here ?>
Each time you issue the
directive, it includes the requested file again, even if you’ve already
inserted it. For instance, suppose that library.php contains a lot of useful
functions, so you include it in your file. Now suppose you also include
another library that includes library.php. Through nesting, you’ve
inadvertently included library.php
twice. This will produce error messages, because you’re trying to define
the same constant or function multiple times. To avoid this problem, use
include_once instead (see Example 5-7).
<?php include_once "library.php"; // Your code goes here ?>
Then, if another
include_once for ...