PHP Advanced and Object-Oriented Programming (2013)

---

2. Add some comments discussing the nature and purpose of this page:

/*
* File name: config.inc.php
* Created by: Larry E. Ullman
* Contact: Larry@LarryUllman.com, LarryUllman.com
* Last modified: June 5, 2012
*
* Configuration file does the following things:
* - Has site settings in one location.
* - Stores URLs and URIs as constants.
* - Sets how errors will be handled.
*/

Because the configuration file is a common file, it ought to be one of the best-documented scripts in a site.

3. Set the email address to be used for errors:

$contact_email = 'address@example.com';

For live sites, I prefer to be emailed when errors occur. To that end, I declare a variable with the “to” email address for any general communications. This may be my address while developing a site but a client’s once the site goes live.

4. Determine whether the script is running on the live server or a test server:

$host = substr($_SERVER ['HTTP_HOST'], 0, 5);
if (in_array($host, array('local', '127.0', '192.1'))) {
$local = TRUE;
} else {
$local = FALSE;
}

I almost always develop on a local server and then upload the completed site to the live server. The two different environments will each have its own server-specific settings. Ideally, the configuration file ought to automatically switch the server-specific settings based on the environment.

To test if the site is running locally, I first grab a reference to the opening five characters in $_SERVER['HTTP_HOST']. I then check if that value is one of a number of possible combinations:

• The word local (as in http://localhost)

• The start of an IP address, 192.1, or 127.0, both of which indicate local networks

You’ll need to adjust this list to values that work best for your local environment.

Whether that conditional is true or not, a $local variable is assigned a Boolean value, for reference later in the script.

5. Set the server-specific constants:

if ($local) {
$debug = TRUE;
define('BASE_URI', '/path/to/html/folder/');
define('BASE_URL', 'http://localhost/directory/');
define('DB', '/path/to/mysql.inc.php');
} else {
define('BASE_URI', '/path/to/live/html/folder/');
define('BASE_URL', 'http://www.example.com/');
define('DB', '/path/to/live/mysql.inc.php');
}

I often use these three constants in my Web applications. The BASE_URI is the absolute file system path to where the site’s root folder is on the server. This constant makes it easy to use absolute references when any script includes a file. If you’re using, for example, XAMPP on Windows, this value might be C:\xampp\htdocs\ch02.

The BASE_URL constant is the host-name and directory (if applicable). On a test server, that might be just http://localhost/ch02/.

Finally, the DB constant is the absolute path to the file that contains the database connectivity information. For security purposes, it’s best to keep this stored outside of the Web directory.

Note that each constant is represented twice: once for a test server and once for the live server. If this is a test server (if $local is TRUE), I also turn on debugging, which will mean more to you shortly.

6. Set the debugging level:

if (!isset($debug)) {
$debug = FALSE;
}

I use a $debug variable to indicate how errors should be handled. If the site is being run locally, $debug will be TRUE by this point. Otherwise, debugging is disabled by default.

To debug a live site, a page would need to use the line

$debug = TRUE;

prior to including the configuration file.

7. Begin a function for handling errors:

function my_error_handler ($e_number, $e_message, $e_file, $e_line, $e_vars) {
global $debug, $contact_email;

PHP allows you to define your own function for handling errors, rather than using the built-in behavior. For more information on this process or the syntax, see the PHP manual or my PHP and MySQL for Dynamic Web Sites: Visual QuickStart Guide book (Peach-pit Press, 2012).

Two global variables will be used in this function.

8. Build up the error message:

$message = "An error occurred in script '$e_file' on line $e_line: $e_message";
$message .= print_r($e_vars, 1);

For debugging purposes, the error message should be as informative as possible. To start, it will include the name of the file where the error occurred and on what line. Then, every existing variable is added. This can be a lot of data , but that’s a good thing when you need to find and fix a problem.

How errors appear when debugging a page.

9. If debugging is turned on, print the error and a backtrace:

if ($debug) { // Show the error.
echo '<div class="error">' . $message . '</div>';
debug_print_backtrace();

If debugging is turned on, then the full message will appear in the Web browser . This is great when developing a site but a huge security flaw on a live site. This specific code will show that information within a DIV that has a class value of error, which presumably matches the corresponding CSS. You can edit this code to fit into your site’s design, whether that means creating a special DIV or whatnot.

Along with the custom error message, a backtrace is printed. A backtrace is a hierarchy of function calls to that point in the program.