Wordpress Change Default Display Name Publicy As for all existing users

Question

does anyone know of way I can change the existing display name publicly as for all users. I want to have firstname lastname as the default because this will reflect in the forum

Answer 1

use this code in function.php this code juste for change display_name and replace with first_name plus first letter for last_name in step the new user or update info for user .

//Change the publicly displayed name on comments
	add_filter('pre_user_display_name','default_display_name');
		function default_display_name($name) {
			 global $current_user;
     		 get_currentuserinfo();
			
		 $lastname=mb_substr($current_user->user_lastname, 0, 1, "UTF-8");
			$name =  ucfirst($current_user->user_firstname) .' '.ucfirst($lastname). '.';
			return $name;
		}