CODEWITHSUNDEEP
c#datetimenullable
user5299399
user5299399

Reputation:

Nullable DateTime setting it getting invalid argument with cannot convert to long

Why do I need to set DateTime as Nullable like this?

DateTime? Err_Rpt_Tm = new DateTime?(DateTime.Now);

Console.WriteLine(Err_Rpt_Tm);

Because I find it odd that in Linqpad when I do this

DateTime Err_Rpt_Tm = new DateTime(DateTime.Now);

I get this error

The best overloaded method match for 'System.DateTime.DateTime(long)' has some invalid arguments

Argument 1: cannot convert from 'System.DateTime' to 'long'

  1. DateTime.Now is never going to be null, so I don't understand the need for nullable DateTime?
  2. convert System.DateTime to long??? I'm explicitly setting DateTime variable "Err_Rpt_Tm"

Upvotes: 0

Views: 328

Answers (2)

Adil
Adil

Reputation: 148150

No DateTime constructor accepts DateTime object although it has constructor for long i.e. DateTime(long ticks) and error is suggesting that constructor to be used.

You can directly assign DateTime.Now to DateTime object and do not need a constructor for this.

DateTime Err_Rpt_Tm = DateTime.Now;

To assign to Nullable DateTime

DateTime? Err_Rpt_Tm = DateTime.Now;

Upvotes: 0

dotnetom
dotnetom

Reputation: 24916

DateTime? is a short-hand for Nullable<DateTime>. Let's look at documentation on MSDN. In constructors section the only available constructor is Nullable<T>(T). This explains why first part of your code compiles.

In second case you are trying to initialize DateTime, and MSDN clearly states that there is no constructor, that accepts single parameter of type DateTime. This is why you get a compile error in second case.

To fix the issue you can use much simpler form of initialization:

DateTime? Err_Rpt_Tm = DateTime.Now;
DateTime Err_Rpt_Tm2 = DateTime.Now;

This is possible because Nullable<T> implements operators for converting nullable type to / from actual type.

Upvotes: 2

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