Lesson 3:
A Place for EverythingWelcome to the third and final lesson for this tutorial. If you've gone through Lesson 1 and Lesson 2, you
already know the essentials for installing and writing useful scripts with MySQL and PHP. We're going to
look at some useful PHP functions that should make your life a lot easier. First, let's look at include files.
We all know the basics of includes, right? Contents of an external file are referenced and imported into the
main file. It's pretty easy: You call a file and it's included. When we do this in PHP there are two functions
we need to talk about : include() and require(). The difference between these two functions is subtle but
important, so let's take a closer look. The require() function works in a XSSI-like way; files are included as
part of the original document as soon as that file is parsed, regardless of its location in the script. So if you
decide to place a require() function inside a conditional loop, the external file will be included even if that
part of the conditional loop is false.
The include() function imports the referenced file each time it is encountered. If it's not encountered, PHP
won't bother with it. This means that you can use include in loops and conditional statements, and they'll
work exactly as planned.
Finally, if you use require() and the file you're including does not exist, your script will halt and produce an
error. If you use include(), your script will generate a warning, but carry on. You can test this yourself by
trying the following script. Run the script, then replace include() with require() and compare the results.
<html>
<body>
<?php
include("emptyfile.inc");
echo "Hello World";
?>
</body>
</html>
I like to use the suffix .inc with my include files so I can separate them from normal PHP scripts. If you do
this, make sure that you set your Web server configuration file to parse .inc files as PHP files. Otherwise,
hackers might be able to guess the name of your include files and display them through the browser as text
files. This could be bad if you've got sensitive information - such as database passwords - contained in the
includes.
So what are you going to do with include files? Simple! Place information common to all pages inside them.
Things like HTML headers, footers, database connection code, and user-defined functions are all good
candidates. Paste this text into a file called header.inc.
<?php
$db = mysql_connect("localhost", "root");
mysql_select_db("mydb",$db);
?>
<html>
<head>
<title>
<?php echo $title ?>
</title>
</head>
<body>
<center><h2><?php echo $title ?></h2></center>
Then create another file called footer.txt that contains some appropriate closing text and tags.
Now let's create a third file containing the actual PHP script. Try the following code, making sure
that your MySQL server is running.
<?php
$title = "Hello World";
include("header.inc");
$result = mysql_query("SELECT * FROM employees",$db);
echo "<table border=1>\n";
echo "<tr><td>Name</td><td>Position</tr>\n";
while ($myrow = mysql_fetch_row($result)) {
printf("<tr><td>%s %s</td><td>%s</tr>\n", $myrow[1], $myrow[2], $myrow[3]);
}
echo "</table>\n";
include("footer.inc");
?>
See what happens? The include files are tossed into the main file and then the whole thing is executed by
PHP. Notice how the variable $title was defined before header.inc is referenced. Its value is made available
to the code in header.inc; hence, the title of the page is changed. You can now use header.inc across all
your PHP pages, and all you'll have to do is change the value of $title from page to page.
Using a combination of includes, HTML, conditional statements, and loops, you can create complex
variations from page to page with an absolute minimum of code. Includes become especially useful when
used with functions, as we'll see down the road.
On to the exciting world of data validation.
Posted in: PHP/MySQL Tutorial
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