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

Question

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
 }

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.

put this somewhere:

public static class DateTimeUtil //or whatever name
{
    public static bool IsEmpty(this DateTime dateTime)
    {
        return dateTime == default(DateTime);
    }
}

then:

DateTime datetime = ...;

if (datetime.IsEmpty())
{
    //unassigned
}

I just found out that GetHashCode() for an unassigned datetime is always zero. I am not sure if this is a good way to check for null datetime, because, I can't find any documentation on why this behavior is displayed.

if(dt.GetHashCode()==0)
{
    Console.WriteLine("DateTime is unassigned"); 
} 

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;