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
include 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, but 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. So you should use
include_once instead (see Example 5-7).
<?php include_once "library.php"; // Your code goes here ?>
Then, whenever another
include_once is encountered, if ...