To Find missing dates in data-gridview.

Question

reg_date	dcotor_name	patient_name	reg_no	Kin_name
1/1/2014	rahul	manmohan	12534	sonia
3/1/2014	narendra	abc	54896	lalu
4/1/2014
10/1/2014

I have two datetimepickers in c# windows form application, when I select date as 01/01/2014 to 31/01/2014 it shows me the date on which doctor was present and other details in datgridview.I have inner join 3-4 tables to get above data. My is how to get missing dates i.e 2/1/2014,5/1/2014 and so on in which doctor was not present.