Get short date for System Nullable datetime (datetime ?) in C#

You need to use .Value first (Since it's nullable).

var shortString = yourDate.Value.ToShortDateString();

But also check that yourDate has a value:

if (yourDate.HasValue) {
   var shortString = yourDate.Value.ToShortDateString();
}

string.Format("{0:d}", dt); works:

DateTime? dt = (DateTime?)DateTime.Now;
string dateToday = string.Format("{0:d}", dt);

Demo

If the DateTime? is null this returns an empty string.

Note that the "d" custom format specifier is identical to ToShortDateString.

That function is absolutely available within the DateTime class. Please refer to the MSDN documentation for the class: http://msdn.microsoft.com/en-us/library/system.datetime.toshortdatestring.aspx

Since Nullable is a generic on top of the DateTime class you will need to use the .Value property of the DateTime? instance to call the underlying class methods as seen below:

DateTime? date;
String shortDateString;
shortDateString = date.Value.ToShortDateString();

Just be aware that if you attempt this while date is null an exception will be thrown.