PHP 101 (Part 1) - Secret Agent Man - Weapons To Die For (
Page 5 of 5 )
If you've used C
before, you're probably already familiar with the "include" directive that
appears near the beginning of every C program. PHP supports two functions which
have a similar job to do - the include() function and the require() function.
Take a look at a simple
example:
<html>
<head>
<title>Weapons Worth Dying For</title>
<style>
h1,h3,li { font-family:Verdana; }
</style>
</head>
<?php
// this time, Bond's going to need the cigarette-lighter gun...
require("./gun.php4");
// the new car-copter...
include("./car.php4");
// and of course, the gold watch with the hidden GPS locator
require("./watch.php4");
?>
<body>
<h3>So, James, here's your check list for the mission.</h3>
<ol type="a">
<li>The gun: <?php echo "$gun"; ?>
<li>The car: <?php echo "$car"; ?>
<li>The watch: <?php echo "$watch"; ?>
</ol>
<br>
<h3>Oh yes...and remember never to let them see you cry. Good luck,
007!</h3>
</body>
</html>
Now, if you try to access this page as it, you'll get a bunch
of error messages warning you about missing files. So you need to create the
files "gun.php4", "car.php4" and "watch.php4":
[gun.php4]
<?php
$gun = "AK-47";
?>
[car.php4]
<?php
$car = "BMW G8";
?>
[watch.php4]
<?php
$watch = "Rolex SAW-007";
?>
And this time, when you access the primary page, PHP should
automatically include the specified files, read the variables $gun, $watch and
$car from them, and display them on the page.
A quick note on the
difference between the include() and require() functions - the require()
function is always replaced by the contents of the file it points to, and
therefore cannot be used in a conditional statement ["if this is true, require
that file"] since the file will be read in regardless. However, the include()
function allows you to optionally include or exclude files on the basis of a
conditional test. Also, a require()d file cannot return values to the main PHP
script, while an included file can.
An important point to be noted is
that when a file is require()d or include()d, the PHP parser leaves "PHP mode"
and goes back to regular "HTML mode". Therefore, all PHP code within the
included external files needs to be enclosed within regular PHP <?...?>
tags.
A very useful and practical application of the include() function
is to use it to include a standard footer or copyright notice across all the
pages of your Web site, like this:
<html>
<head>
<title></title>
</head>
<body>
...your HTML page...
<br>
<?
include("footer.html");
?>
</body>
</html>
where "footer.html" contains
<font size=-1
face=Arial>This material copyright Melonfire, 2000. All rights
reserved.</font>
Now, this footer will appear on each and every
page that contains the include() statement above - and, if you need to change
the message, you only need to edit the single file named
"footer.html"!
And that's about it for this week. We've shown you the
basic building blocks of PHP - its variables and operators - and next time,
we'll be using those fundamental concepts to demonstrate PHP's powerful form
processing capabilities. Don't miss it!
