If you are developing a plugin on WordPress, you will need to debug your code as you go.

To enable debugging, go to your wp-config.php file.

Find the line…
[source language=“php“]define(‚WP_DEBUG‘, false);[/source]

Replace the line above with the following…
[source language=“php“]
// Turns WordPress debugging on
define(‚WP_DEBUG‘, true);

// Tells WordPress to log everything to the /wp-content/debug.log file
define(‚WP_DEBUG_LOG‘, true);

// Doesn’t force the PHP ‚display_errors‘ variable to be on
define(‚WP_DEBUG_DISPLAY‘, false);

// Hides errors from being displayed on-screen
@ini_set(‚display_errors‘, 0);
[/source]

Now you all warnings and errors will show up in the /wp-content/debug.log file, including WordPress warnings of deprecated functions.

You can write directly to this log from your plugin using the error_log() function.

Typically…
[source language=“php“]
//output some debug string
error_log( ‚this works yo‘ );

//output some array/object
error_log( print_r( $some_obj_or_array, 1 ) );
[/source]

Kudos to this post. It has some good plugin development tips, including how to enable debugging on WordPress.