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.
--
mo*******@nospam.nospam

[José Joye]

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" <mo*******@nospam.nospam> wrote in message
news:Ok**************@TK2MSFTNGP14.phx.gbl...

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.
--
mo*******@nospam.nospam

[Kevin Yu [MSFT]]

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]]

moondaddy wrote:

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?

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

Jon

[moondaddy]

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

--
mo*******@nospam.nospam
"Jon Skeet [C# MVP]" <sk***@pobox.com> wrote in message
news:11*********************@z34g2000cwc.googlegro ups.com...

moondaddy wrote:

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?

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

Jon