在Windows中使用或不使用域登录用户名

Is there a direct API to get the currently logged in user's name with the domain? So, it would return something like "domain\user" when a machine is on the domain, but at the same time it would return "user" when the machine is not on the domain? If there's not, what's the best way to get this information?Is there a direct API to get the currently logg