Read-only and Constant

Question

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

Vineet Kumar Saini · Answer

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.....

Vulpes · Answer

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 Agarwal · Answer

Check the following link http://blogs.msdn.com/b/csharpfaq/archive/2004/12/03/274791.aspx