Read-only and Constant

Akshay Teotia

14y2.3kVisual Basic .NET

Hi Friends

Can anybody differenciate between the term Read-only and Constant?

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vineet Kumar Saini14y ago
Hi Akshay.....

Const – Compile-Time Constant Values
Readonly - Runtime Constant References

The difference is that the value of readonly field is set at run time, so it can have a different value for different executions of the program. However, the value of a const field is set to a compile time constant.

A const field can only be initialized at the declaration of the field. A readonly field can be initialized either at the declaration or in a constructor.
When using const, the value has to be set before compiling, and can not be changed.
when using readonly, the value is set when the instance is created. This means that you can specify the value of the readonly in the constructor of your class.
Another difference between const and readonly, is that const are static by default, where with readonly, you must define it as static (if you want it to be).

Thanks.....
Vulpes14y ago
The difference is that a constant field is evaluated statically at compile time but a readonly field is evaluated dynamically at runtime.

This means in practice that constant fields are limited to the pre-defined types (int, bool, char, double, string etc) which support literal values but readonly fields are not limited in this way.

Whereas constants always need to be defined where they're declared, readonly fields can either be defined in this way or from within a constructor.

Constants are implcitly static, but readonly fields can either be instance or static.

Also, you can declare constants which are local to a method or property but you can't do this with readonly values.
Karthik Agarwal14y ago
Check the following link

http://blogs.msdn.com/b/csharpfaq/archive/2004/12/03/274791.aspx