Null value for DateTime in C#

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Hi, i want to reset DateTime values for my database in a C# program but it seems DateTime can't be nulled. Any advice on how to do it or if not how to reset the DateTime value? Thanks in advance.

Posted 22-Oct-13 20:17pm

YourAverageCoder

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Thanks7872 23-Oct-13 2:23am

What do you mean by "reset DateTime value"?

Timberbird 23-Oct-13 2:25am

DateTime is a structure, so yes, it can't be nulled. You could try using DateTime.MinValue as a special "non-defined date and time" value

YourAverageCoder 23-Oct-13 2:26am

Thanks. I would have rated your answer but i can't since it's posted as a comment.

Sergey Alexandrovich Kryukov 23-Oct-13 2:35am

I'm sure this is a wrong answer. Please see my comment.
—SA

Timberbird 23-Oct-13 2:40am

Glad I could help. It's just the first thing that came to my mind - possibly there's a better solution (like using nullable DateTime, i.e. "DateTime?" - it's possile, but I'm not sure which is more suitable for you)

Sergey Alexandrovich Kryukov 23-Oct-13 2:35am

Not quite so. I don't know about such "non-defined" value. I think it does not exist. (Do you think I'm wrong? Then, please, give us a link.)

Right approach is using nullable DateTime. All non-nullable types can be used as a base of a nullable type. Please see my answer.

—SA

Timberbird 23-Oct-13 2:45am

Oh, I posted the second comment about nullable DateTime before I saw your comment and solution. I didn't mean there's a special "non-defined" value in .NET Framework, it just can be considered so by program logic - some kind of magic number

Sergey Alexandrovich Kryukov 23-Oct-13 2:49am

"Magic numbers" is evil, should be avoided. I think what I explained in my answer is the real way to go.

—SA

Timberbird 23-Oct-13 2:58am

Absolutely agree about avoiding the magic numbers, but some are quite popular - how often do you see usage of String.Empty (or plain "") when it's not truly necessary? :) Using DateTime.MinValue adds the same - maybe questionable - advantages: for example, you can call methods like .Equals() or .ToString() of the object without extra checks and a danger of getting NullReferenceException

Sergey Alexandrovich Kryukov 23-Oct-13 3:07am

Nullable is conceptually better. And the "danger" of this exception is fully balanced by the possibility of checking up for null, which is the ultimate purpose of nullable. One cannot enjoy some feature and blame this feature at the same time.
Your example of "special" values are much more legitimate then default(DateTime) or DateTime.MinValue, which are quite legitimate nothing special points in time...
—SA

Timberbird 23-Oct-13 3:23am

And the same goes for empty strings, since it rarely matters if string value is empty or null, though conceptually these are different values with different meaning and must be differentiated at all times. The main problem with DateTime.MinValue I see is the common problem with all magic numbers - these can't be told from actual business data (if user indeed tries to enter minimal DateTime value possible, why should we restrict him?). In that sense I totally agree with you - nullable types are better

Sergey Alexandrovich Kryukov 23-Oct-13 12:02pm

That's the point: an attempt to force the developer/user to tread minimal value as "special", "not time" would be the restriction, so adding one extra value (null) is beneficial.
—SA

2 solutions

Solution 2

Hi ,

You can send a value to data base using

C#

DateTime.MinValue

Thanks,
Nani.

Posted 22-Oct-13 20:42pm

Nani Babu

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-10-22T20:33:00

This is a structure, a value type and hence is not nullable. You can make a member or a variable of System.DateType nullable if you use the type System.DateType? instead:

C#

System.DateType? myTime = null;

//...

if (myTime == null) //...

Please see: http://msdn.microsoft.com/en-us/library/1t3y8s4s%28v=vs.90%29.aspx[^].

Semantically, it looks like you complement the value set of any non-nullable type with one extra point: null value, that's all. I don't advise to try to use "reset value" (like default(System.DateTime)). The default value is a valid point of time, it cannot be considered as "no time". Don't use it, better use the nullable type.

—SA