PHP Errors, Warnings, and Notices
Enabling WP_DEBUG will cause all PHP errors, notices and warnings to be displayed. This is likely to modify the default behavior of PHP which only displays fatal errors and/or shows a white screen of death when errors are reached.
Showing all PHP notices and warnings often results in error messages for things that don't seem broken, but do not follow proper data validation conventions inside PHP. These warnings are easy to fix once the relevant code has been identified, and the resulting code is almost always more bug-resistant and easier to maintain.
Deprecated Functions and Arguments
Enabling WP_DEBUG will also cause notices about deprecated functions and arguments within WordPress that are being used on your site. These are functions or function arguments that have not been removed from the core code yet but are slated for deletion in the near future. Deprecation notices often indicate the new function that should be used instead.
WP_DEBUG_LOG
WP_DEBUG_LOG is a companion to
WP_DEBUG that causes all errors to also be saved to a
debug.log log file inside the
/wp-content/ directory. This is useful if you want to review all notices later or need to view notices generated off-screen (e.g. during an
AJAX request or
wp-cron run).
Note that this allows you to write to /wp-content/debug.log using PHP's built in error_log() function, which can be useful for instance when debugging AJAX events.
define( 'WP_DEBUG_LOG', true );
Note: for WP_DEBUG_LOG to do anything, WP_DEBUG must be enabled (true). Remember you can turn off WP_DEBUG_DISPLAYindependently.
WP_DEBUG_DISPLAY
WP_DEBUG_DISPLAY is another companion to WP_DEBUG that controls whether debug messages are shown inside the HTML of pages or not. The default is 'true' which shows errors and warnings as they are generated. Setting this to false will hide all errors. This should be used in conjunction with WP_DEBUG_LOG so that errors can be reviewed later.
define( 'WP_DEBUG_DISPLAY', false );
Note: for WP_DEBUG_DISPLAY to do anything, WP_DEBUG must be enabled (true). Remember you can control WP_DEBUG_LOGindependently.
SCRIPT_DEBUG
SCRIPT_DEBUG is a related constant that will force WordPress to use the "dev" versions of core CSS and JavaScript files rather than the minified versions that are normally loaded. This is useful when you are testing modifications to any built-in .js or .css files. Default is false.
define( 'SCRIPT_DEBUG', true );
SAVEQUERIES
The SAVEQUERIES definition saves the database queries to an array and that array can be displayed to help analyze those queries. The constant defined as true causes each query to be saved, how long that query took to execute, and what function called it.
define( 'SAVEQUERIES', true );
The array is stored in the global $wpdb->queries.
NOTE: This will have a performance impact on your site, so make sure to turn this off when you aren't debugging.
Example wp-config.php for Debugging
The following code, inserted in your
wp-config.php file, will log all errors, notices, and warnings to a file called debug.log in the wp-content directory. It will also hide the errors so they do not interrupt page generation.
// Enable WP_DEBUG mode
define( 'WP_DEBUG', true );
// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );
// Disable display of errors and warnings
define( 'WP_DEBUG_DISPLAY', false );
@ini_set( 'display_errors', 0 );
// Use dev versions of core JS and CSS files (only needed if you are modifying these core files)
define( 'SCRIPT_DEBUG', true );
NOTE: You must insert this
BEFORE /* That's all, stop editing! Happy blogging. */ in the
wp-config.php file
