Referencing one class within another

Hi

I'm trying to get my head around this with classes. What I'm trying to do is use one class's functions within another class. Probably easier if I just show some code:

class DB
{
var $prefix;

function DB($host, $db_user, $db_pswd, $db_name, $db_prefix)
{
// Connect
$open = mysql_connect($host, $db_user, $db_pswd)
or die('Unable to connect');
$db = mysql_select_db($db_name, $open);

// Set the prefix var
$this->prefix = $db_prefix;
}
}

class Test
{
function hello()
{
return $db->prefix; // Here lies the problem!
}
}

And my index file looks like this at the top:

$db = new DB($host, $db_user, $db_pswd, $db_name, $db_prefix);
$test = new Test();

echo $db->prefix; // Works!
echo $test->hello(); // Does not work!


Now, I can access the DB class just fine, everything works alright with the $db variable etc, but what I don't understand is how I can use DB within my new Test class. The error generated is a "Call to a member function on a non-object" on the row where I try to do this.

Confused!

2 ways, , actually 3 depends on your situation which you will use

<?php
class Test{
function test(&$db){
$this->db=$db;
}

function hello(){
return $this->db->prefix;
}
}
$db = new DB($host, $db_user, $db_pswd, $db_name, $db_prefix);
$test = new Test($db);
echo $test->hello(); // should work
?>

OR you can aggregate the db class within test... though to avoid passing connection parameters around you are better off calling a static instance of your DB class...

<?
class Test{
function test(){
$this->db=new static_instance_of_db();
}

function hello(){
return $this->db->prefix;
}
}
?>

?>
or you can just make $db global :(

google for `singleton` or `static instance` (easier in PHP5 than 4)

Thank you, that first method works great. And I understand it as well! :) Much appreciated.