How to work with a DATE type in a COM/ATL project

I've got an ATL method that takes a DATE type, which is really a double. I ca开发者_高级运维n't find the class/functions for this type. Does anyone know how to operate on this type? I just need to make it into something I can get into boost::gregorian::date (yyyy/mm/dd). Also, I would really like to know what this double represents. Thanks.

With ATL use COleDateTime for VT_DATE variants.