How can I use error_log() with WordPress?

Question

I'm trying to use error_log() in a custom WordPress plugin I am building but for some reason, I can't.

When I use error_log() my site just breaks, but I'm not seeing any errors in debug.log.

I have setup debugging in my wp_config.php file like this:

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);

Stranegly, if I use error_log() in my theme, the site doesn't break, but nothing is output to debug.log either.

What do I need to do to be able to use error_log() in my WordPress plugin and theme?

I'm using WordPress 3.9.1.

Answer 1

According to the Codex, WP_DEBUG_DISPLAY should be set to true by default, but it would seem that was not the case.

Adding define('WP_DEBUG_DISPLAY', true); to wp_config.php fixed the error logging.

Setting WP_DEBUG_DISPLAY to false removed the errors from the browser but allowed them to be output in the log.

It would seem that Wordpress requires define('WP_DEBUG_DISPLAY'); to output errors to the log whether you set it to be true or false.