Chandradev's Blog

Hi

Const and readonly perform a similar function on data members, but they have a few important differences.

Const

A constant member is defined at compile time and cannot be changed at runtime. Constants are declared as a field, using the const keyword and must be initialized as they are declared. For example;

public class MyClass
{
public const double PI = 3.14159;
}

PI cannot be changed in the application anywhere else in the code as this will cause a compiler error.

Constants can be marked as public, private, protected, internal, or protected internal.

ReadOnly

A read only member is like a constant in that it represents an unchanging value. The difference is that a readonly member can be initialized at runtime, in a constructor as well being able to be initialized as they are declared. For example:

public class MyClass
{
public readonly double PI = 3.14159;
}

or

public class MyClass
{
public readonly double PI;

public MyClass()
{
PI = 3.14159;
}
}