Add rewrite rules doesn't work

Hi. I want rewrite an URL:
http://localhost/?post_type=cd&cd=cdname&singers=singername to http://localhost/cd/cdname-singername

So I wrote this code:
add_rewrite_rule('cd/([^/]*)-([^/]*)$','index.php?post_type=cd&cd=$matches[1]&singers=$matches[2]','top');
But it doesn’t work.

If I wrote:
^cd/([^/]*)/([^/]*)? instead ^cd/([^/]*)-([^/]*)? ( http://localhost/cd/cdname/singername instead http://localhost/cd/cdname-singername ) it works…

How can I resolve? Thanks.