Checking to see if a DateTime variable has had a value assigned

Question

Is there an easy way within C# to check to see if a DateTime instance has been assigned a value or not?

Answer 1

The only way of having a variable which hasn't been assigned a value in C# is for it to be a local variable - in which case at compile-time you can tell that it isn't definitely assigned by trying to read from it :)

I suspect you really want Nullable<DateTime> (or DateTime? with the C# syntactic sugar) - make it null to start with and then assign a normal DateTime value (which will be converted appropriately). Then you can just compare with null (or use the HasValue property) to see whether a "real" value has been set.

Answer 2

Use Nullable<DateTime> if possible.

Answer 3

DateTime is value type, so it can not never be null. If you think DateTime? ( Nullable ) you can use:

DateTime? something = GetDateTime();
bool isNull = (something == null);
bool isNull2 = !something.HasValue;

Answer 4

do you mean like so:

DateTime datetime = new DateTime();

if (datetime == DateTime.MinValue)
{
    //unassigned
}

or you could use Nullable

DateTime? datetime = null;

 if (!datetime.HasValue)
 {
     //unassigned
 }

Answer 5

Thanks guys, sorry I cant give you all the 'answer' token :)

Answer 6

I generally prefer, where possible, to use the default value of value types to determine whether they've been set. This obviously isn't possible all the time, especially with ints - but for DateTimes, I think reserving the MinValue to signify that it hasn't been changed is fair enough. The benefit of this over nullables is that there's one less place where you'll get a null reference exception (and probably lots of places where you don't have to check for null before accessing it!)