Working Through a Book - Undefined Variable

[BorysSokolov]

I'm working through an example in the book Pro PHP and jQuery by Jason Lengstorf, and keep receiving the error

Notice: Undefined variable: db in ...\sys\class\class.db_connect.inc.php on line 30

I do know why I am receiving the error, but I am not sure how to go about solving it. I'm not exactly sure what the author meant to do with the variable db.

 

Here's the code:

class DB_Connect {
	/**
	 * Stores a database object
	 *
	 * @var object A database object
	 */
	protected $db;
	 
	/**
	 * Checks for a DB object or creates one if one isn't found
	 *
	 * @param object $dbo A database object
	 */
	protected function __construct($dbo=NULL)//assigns $dbo a default value
	{
		if(is_object($db)){
			$this->db = $db;
		}else{
			//Constants are defined in /sys/config/db-cred.inc.php
			$dsn = 'mysql:host=' . DB_HOST . ';dbname=' . DB_NAME;
			try{
				$this->db = new PDO($dsn, DB_USER, DB_PASS);
			}catch(Exception $e){
				//If the DB connection fails, output the error
				die($e->getMessage());
			}
		}
	}
}

Nowhere in the code is the variable ever assigned a value, or even declared, prior to making the check, so I'm not even sure what's it supposed to do. I double-checked that I haven't missed any code, but surely I must have omitted something...

 

Can anyone figure it out?

[Jessica]

The function parameter is $dbo. Then you look for $db.

[BorysSokolov]

I changed the parameter from $dbo to $db, and now everything works fine. I suppose I should have reviewed the code before posting.