Process wider date range than COleDateTime

I have a ULONGLONG variable uDate which express the number of dates starting from 0001-01-01, up to 9999-12-31. Now I want to convert it into a string like this

‘yyyy-mm-dd’.

However, the COleDateTime can only express the date from 100 to 9999, smaller than what I need. So are there any third-party classes or libraries that can express this. Or make the conversion from uDate to CString?

Thanks

AFAIK COleDateTime's underlying object type is DATE (which is double, not ULONGLONG)
So where does your ULONGLONG date come from? And how are date parts stored there?