Memcached不在php中工作

I can't make memcache work. I followed this tutorial and when I try the example from the last part of the tutorial I don't get any output.

Here's the code from the tutorial.

$m = new Memcached();
$m->addServer('localhost', 11211);
$m->set('key', 'hello world');
var_dump($m->get('key'));

When I load it to my webpage I don't get any output. It says error. What's wrong with my server? I installed it correctly and checked my phpinfo and found it there. why can't I make it work?

UPDATE:

I'm using virtualbox.. and debian is my guest os. and everything is working in php it's just that i can't make it work for memcached

Start memcached daemon in the terminal like so:

memcached -vv -m64 -l127.0.0.1