C# enum - is it null?

Question

I have the following code in a User Control:

public partial class MyControl : System.Web.UI.UserControl
{    
    public Enums.InformationSubCategory SubCategory { get; set; }

    ...omitted code
}

Enums.InformationSubCategory is an enum I have defined elsewhere, with the idea being that I can do this:

Example 1. <my:MyControl runat="server" SubCategory="Food" ...... />
Example 2. <my:MyControl runat="server" ...... />

If I don't specify a value at all for SubCategory, what will the value of SubCategory be in the code-behind for MyControl? Is it null or does a default value get applied to it? I noticed that with int properties, it defaults to zero.

CodesInChaos · Accepted Answer · 2011-10-07 12:26:49Z

2

Fields get initialized to default(T). The easy way to remember what the default value of some type is that it corresponds to binary zero in the obvious implementation.

For an enum this means that the underlying integer type is set to 0. By default this corresponds to the first value defined in the enum.

That's why it's common to name the first value in an enum None.

edited Oct 7, 2011 at 12:26

answered Oct 7, 2011 at 11:59

CodesInChaos

109k26 gold badges224 silver badges267 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Jakub Konecki Over a year ago

'the first value defined in the enum' - assuming no explicit value has been assigned, ie. enum Foo { Bar = 1, None = 0 }

CodesInChaos Over a year ago

Yes, that's why I said "By default".

Arj Over a year ago

@CodeInChaos What if I have assigned non-zero integers to all of the enum members?

CodesInChaos Over a year ago

Then it will still become 0. It's an unnamed value. Enums can have all values of the underlying integer type, even those that have no name.

Alon Adler · Accepted Answer · 2011-10-07 12:01:14Z

0

The default underlying type of the enumeration elements is int. By default, the first enumerator has the value 0, and the value of each successive enumerator is increased by 1. For example:

enum Days {Sat, Sun, Mon, Tue, Wed, Thu, Fri};

In this enumeration, Sat is 0, Sun is 1, Mon is 2, and so forth. Enumerators can have initializers to override the default values.

enum Days {Sat=1, Sun, Mon, Tue, Wed, Thu, Fri};

In this enumeration, the sequence of elements is forced to start from 1 instead of 0.

answered Oct 7, 2011 at 12:01

Alon Adler

4,0345 gold badges34 silver badges45 bronze badges

1 Comment

Arj Over a year ago

Great explanation on enums but doesn't answer the question!

Jakub Konecki · Accepted Answer · 2011-10-07 12:26:48Z

0

It will be 0, as your enum is by default based on Int32.

edited Oct 7, 2011 at 12:26

answered Oct 7, 2011 at 11:58

Jakub Konecki

46.1k8 gold badges92 silver badges128 bronze badges

3 Comments

Henk Holterman Over a year ago

It will be 0 but it could be a byte or short.

Jakub Konecki Over a year ago

@Henk - That's why I said 'by default'.

Henk Holterman Over a year ago

Yes, you're right. I thought the compiler was free to choose. msdn.microsoft.com/en-us/library/cc138362.aspx

Collectives™ on Stack Overflow

C# enum - is it null?

3 Answers 3

4 Comments

1 Comment

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

1 Comment

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related