DateTime.hasvalue vs datetime == null, which one is better and why

Question

i'd like to ask a question about controlling null value of a datetime.

if (mydatetime != null)

or

if(mydatetime.hasvalue)

which one is better, or proper and why?

thank you.

They are not exactly equivalent. `HasValue` is only if the var is a Nullable — Ňɏssa Pøngjǣrdenlarp, Jun 27 '16 at 15:18
The first is true if it has a value, the second is true if it has no value. There is probably a `!` too much. — René Vogt, Jun 27 '16 at 15:19
mine is nullable datetime (datetime? my datetime=null), in this case is there any difference? — Aurora, Jun 27 '16 at 15:19

sujith karivelil · Answer 1 · 2019-07-17T14:08:16.290

The First comparison with !=null is a valid comparison, whereas the second can be used only if the variable is declared as Nullable, Or in other words comparison with .HasValue can only be used when the DateTime variable is declared as Nullable

For example :

DateTime dateInput; 
// Will set the value dynamically
if (dateInput != null)
{ 
   // Is a valid comparison         
}
if (dateInput.HasValue)
{ 
   // Is not a valid comparison this time        
}

Where as

DateTime? dateInput; // nullable declaration
// Will set the value dynamically
if (dateInput != null)
{ 
   // Is a valid comparison         
}
if (dateInput.HasValue)
{ 
   // Is also valid comparison this time        
}

score 3 · Answer 2 · edited May 24 '21 at 14:47

If you ask

if (mydatetime != null)

you are checking whether the variable has been instantiated.

If it actually is not instantiated the following statement will give you a NullReferenceException

if(!mydatetime.hasvalue)

because you are trying to access a property of an object that is null

Only if you declare the DateTime as Nullable will it display the same behaviour.

Nullable<DateTime> mydatetime = null;

Console.WriteLine(mydatetime.HasValue);

DateTime.hasvalue vs datetime == null, which one is better and why

2 Answers2