Create an constant array in c#

Strictly speaking you can not, since the constellation can only be applied to a field or local whose value is known at compile time.

In both the lines below, the right-hand is not a constant expression (not in C#).

1. const int [] constIntArray = newint [] {2, 3, 4};
2. // error CS0133: The expression being assigned to 'constIntArray' must be constant
3. const int [] constIntArrayAnother = {2, 3, 4};
4. // error CS0623: Array initializers can only be used in a variable or field
5. //               initializer. Try using a new expression instead.

However, there are some workarounds, depending on what it is you want to achieve.

If want a proper .NET array (System.Array) that cannot be reassigned, then static readonly will do for you.

static readonly int [ ] constIntArray = new int[] {1, 2, 3};

The constIntArray field will be initialized before it its first use.

If, however, requires a constant set of values (such as an argument to an attribute constructor), then - if you may be limited to integral types - an enum would serve well.

For example:

1. [Flags]
2. public enum Role
3. {
4.     Administrator = 1,
5.     BackupOperator = 2,
6.     // etc.
7. }
8.  
9. public class RoleAttribute : Attribute
10. {
11.     public RoleAttribute()
12.     {
13.         CreateRole = DefaultRole;
14.     }
15.  
16.     public RoleAttribute(Role role)
17.     {
18.         CreateRole = role;
19.     }
20.  
21.     public Role CreateRole
22.     {
23.         get { return this.createRole; }
24.         set { this.createRole = value; }
25.     }
26.  
27.     private Role createRole = 0;
28.     public const Role DefaultRole = Role.Administrator
29.      | Role.BackupOperator;
30. }
31.  
32. [RoleAttribute(RoleAttribute.DefaultRole)]
33. public class DatabaseAccount
34. {
35.     //..............
36. }

RoleAttribute, instead of taking a series, only have a single argument of the flags (appropriately or-ed). If the underlying type of the list is long or ulong paper, which offers 64 different functions.