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I was looking through some code the other day and I saw something like (int?) and I dont think Ive ever see that before. What does it mean when you use a ? after a type?

Leroy Jenkins
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7 Answers7

13

It is short for Nullable<T>.

Nullable types in C#

This is a generic struct that can wrap a value-type to add the value null. To make the use of this type more convenient C# adds quite a bit of compiler-magic. Such as the short-name T?, lifted operators,...

The following thread on SO is interesting too: ? (nullable) operator in C#

Community
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CodesInChaos
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  • And the parenthesis is for casting, but you probably knew that. – Svish Mar 09 '11 at 13:12
  • I thought the OP used the parentheses as a kind of quotation-marks. But casting makes sense too. To decide that we'd need more context. – CodesInChaos Mar 09 '11 at 13:14
  • I understand casting, thats not a problem (obviously you didnt know I knew that) so I apologize if I was a bit vague. My main concern was in fact the Nullable portion. The "syntactic sugar" is so difficult to google. Thanks again. – Leroy Jenkins Mar 09 '11 at 13:38
  • I agree. Not being able to search for them makes even otherwise trivial problems annoying. – CodesInChaos Mar 09 '11 at 13:58
6

It's a variation/alternative of the Nullable<Type>. Have seen it used a lot with DateTime to avoid the default DateTime value which gives an error in DB columns related to dates. Quite useful actually.

gnikolaropoulos
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5

int? is syntactic sugar for Nullable<int>.

CheeZe5
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4

That is the shorthand syntax for Nullable<T> (or in your case Nullable<int>).

This is used when you need value types to be null, such as int, Boolean and DateTime.

Daniel Hilgarth
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alexn
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3

it means Nullable, so our value-type variable can be null

Andrey
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3

the ? after the type implies that the type can have null value besides its normal values.

I've seen the use mostly for database related types where you have Nullable columns

Maverik
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3

As other people have said int? is short for Nullable<int>.

This article is a couple of years old now but it's a good explanation of nullable types

Fermin
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