8.19. Logging Debugging Information
Problem
You want to make debugging easier by adding statements to print out variables. But, you want to easily be able to switch back and forth from production and debug modes.
Solution
Put a function that conditionally prints out messages based on a
defined constant in a page included using the
auto_prepend_file
configuration setting.
Save the following code to debug.php:
// turn debugging on define('DEBUG',true); // generic debugging function function pc_debug($message) { if (defined('DEBUG') && DEBUG) { error_log($message); } }
Set the auto_prepend_file
directive in
php.ini:
auto_prepend_file=debug.php
Now call pc_debug( )
from your code to print out debugging
information:
$sql = 'SELECT color, shape, smell FROM vegetables'; pc_debug("[sql: $sql]"); // only printed if DEBUG is true $r = mysql_query($sql);
Discussion
Debugging code is a necessary side-effect of writing code. There are a variety of techniques to help you quickly locate and squash your bugs. Many of these involve including scaffolding that helps ensure the correctness of your code. The more complicated the program, the more scaffolding needed. Fred Brooks, in The Mythical Man-Month, guesses that there’s “half as much code in scaffolding as there is in product.” Proper planning ahead of time allows you to integrate the scaffolding into your programming logic in a clean and efficient fashion. This requires you to think out beforehand what you want to measure and record and how you ...
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