Wordpress Function for Functions.php, Get The Current Username from Anywhere

functions.php

// get the current user name from anywhere
// paste into functions.php
if ( ! function_exists( 'get_user_name' ) ) {
	function get_user_name() {
		global $current_user;
		get_currentuserinfo();//populates current user var/object
		$current_visible_name = $current_user->user_firstname;
		if($current_visible_name == '') {
			$current_visible_name = $current_user->display_name;
		};
		echo $current_visible_name;
	}
}
add_action("get_current_user_name","get_user_name");