March 2015 Boston PHP presentation covering the debugging chapter of PHP and MySQL for Dynamic Web Sites: Visual QuickPro Guide.

1. Debugging
David Kelleher
www.davidk.net

2. Debugging
Testing and fixing code errors can be more than
50% of development costs

3. display_errors
• Do not use display_errors in Production (Live Site)
• Use error_log instead to write errors to a file
• Trick for using on scripts with parse errors:
error_reporting(E_ALL);
ini_set("display_errors", 1);
include 'file_with_error.php';

4. Spelling Errors
Use consistent capitalization
• PHP Class names: Capitalized
• PHP Variable & Object names: camelCase
• PHP Constants: UPPERCASE
• MySQL Tables & Fields: lowercase_with_underscores

5. Punctuation Errors
Wordpress Example:
http://uglycode.com/tag/ugly-names/
$Fname =
sanitize_title_with_dashes(substr(
$Fid, $fQ+1, strpos($Fid,'"',$fQ+1)-
$fQ-1 ));

6. Unbalanced Quotations
Use syntax highlighting to spot missing quotes

7. Unbalanced Curly Braces
Unexpected $end
Unexpected }
• These types of parse errors occur when you have
extra curly braces, missing curly braces, or ones
in the wrong places.
• Format your code with standard indenting is more
readable and makes spotting these errors easier.

8. Headers Already Sent
Warning: Cannot modify header information -
headers already sent
<?php
// The extra space causes an error.
header('Location: http://test.com');

9. Logic Errors
Solve with pencil and paper
• Flowcharts
• State Diagrams

10. Debugging
David Kelleher
www.davidk.net