Explain the '?' in: int? a = null;

[moondaddy]

I'm learning c# and see a code example where a value of null is assigned to
a variable:

int? a = null;

I could not find this in the docs. can someone please explain exactly what
the '?' is? and where-all it can be used?

Thanks.


--
moondaddy@nospa m.nospam

[José Joye]

Re: Explain the '?' in: int? a = null;

You should search for "nullable types" in documentation.

In short this allow value types to have null assigned to them. It is a
shorthand for creating a variable of the generic System.Nullable <T>
structure type.

-José


"moondaddy" <moondaddy@nosp am.nospam> wrote in message
news:Ok$jWLcPGH A.1216@TK2MSFTN GP14.phx.gbl...[color=blue]
> I'm learning c# and see a code example where a value of null is assigned[/color]
to[color=blue]
> a variable:
>
> int? a = null;
>
> I could not find this in the docs. can someone please explain exactly[/color]
what[color=blue]
> the '?' is? and where-all it can be used?
>
> Thanks.
>
>
> --
> moondaddy@nospa m.nospam
>
>[/color]

[Kevin Yu [MSFT]]

RE: Explain the '?' in: int? a = null;

Hi moondaddy,

The question mark means that variable is a nullable type. Nullable types
represent value-type variables that can be assigned the value of null. You
cannot create a nullable type based on a reference type. (Reference types
already support the null value.)

You can check the following link for more information:

http://msdn2.microsoft.com/en-us/library/1t3y8s4s.aspx

Kevin Yu
=======
"This posting is provided "AS IS" with no warranties, and confers no
rights."

[Jon Skeet [C# MVP]]

Re: Explain the '?' in: int? a = null;

moondaddy wrote:[color=blue]
> I'm learning c# and see a code example where a value of null is assigned to
> a variable:
>
> int? a = null;
>
> I could not find this in the docs. can someone please explain exactly what
> the '?' is? and where-all it can be used?[/color]

It's a new feature in C# 2.0. See
http://www.pobox.com/~skeet/csharp/c.../nullable.html for more
information.

Jon

[moondaddy]

Re: Explain the '?' in: int? a = null;

Thanks to all that replied. This helps and the links were good too!

--
moondaddy@nospa m.nospam
"Jon Skeet [C# MVP]" <skeet@pobox.co m> wrote in message
news:1141287167 .592468.87380@z 34g2000cwc.goog legroups.com...[color=blue]
> moondaddy wrote:[color=green]
>> I'm learning c# and see a code example where a value of null is assigned
>> to
>> a variable:
>>
>> int? a = null;
>>
>> I could not find this in the docs. can someone please explain exactly
>> what
>> the '?' is? and where-all it can be used?[/color]
>
> It's a new feature in C# 2.0. See
> http://www.pobox.com/~skeet/csharp/c.../nullable.html for more
> information.
>
> Jon
>[/color]