Including and Requiring Files
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. Youâll also probably start using libraries created by other programmers.
Thereâs 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
and require
.
The include Statement
Using include
, you can tell PHP
to fetch a particular file and load all its contents. Itâs 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 ?>
Using include_once
Each time you issue the include
directive, it includes the requested file again, even if youâve 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, youâve
inadvertently included library.php
twice. This will produce error messages, because youâre 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 ...
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