Can a DateTime be null? [duplicate]

问题:

Possible Duplicate:
DateTime “null” value

is it possible to set datetime object to null?

回答1:

DateTime is a value type, which, just like int and double, has no meaningful null value.

In VB.NET, you can write this:

Dim d As DateTime = Nothing

But all this does is to set d to the default DateTime value. In C# the equivalent code would be this:

DateTime d = default(DateTime);

...which is equivalent to DateTime.MinValue.

That said, there is the Nullable<T> type, which is used to provide a null value for any value type T. The shorthand for Nullable<DateTime> in C# is DateTime?.

回答2:

DateTime? myDate = null;

The question mark will give you a nullable type. The one that can either be set to its native value or to null.

DateTime itself is a value type. It cannot be null.

回答3:

Nope, you cannot for DateTime is a value type.

You might want to look at Nullable<DateTime> though (or DateTime? in short)

回答4:

No -- DateTime is a struct in C# and structs (value types) can not be null.

You can, however, use Nullable<DateTime>.

回答5:

No, its a structure not a class. Either make it a nullable type, e.g. System.DateTime? myValue; or use the System.DateTime.MinValue as a sentinel.

回答6:

Normally DateTime cannot be null, since is a Value Type, but using the nullable operator introduced in C# 2, you can accomplish this