Difference Between Readonly And Constant in C#
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Difference Between Readonly And Constant in C#

Editorial Team
Editorial Team

A question that several new C# developers ask me a lot is the difference between readonly and constant keyword. In this post, I'll explain the difference between these two keywords.

Declaring constant and Readonly fields

In C#, constants can be declared with the const keyword and read-only fields can be declared using the readonly keyword.

class Person
	public const string Planet = "Earth";
	public readonly string Name;

Understanding The Difference

Now, let us try to understand the difference between const and readonly.

Difference 1: Constants should be initialized with a value.

The first difference between a constant and a readonly variable is that a constant should be initialized with a value when it is created and readonly fields can be declared without providing a value.

So, the correct way to declare a constant is:

Difference 2: Constants are static by default

The second difference is that the constant fields are static by default. Therefore, we cannot access a constant field of the class in the context of an object.

Difference 3: The value of a readonly member can be changed from the constructor.

Unlike constants, whose value cannot be changed, once created, the value of a readonly member can be assigned from the constructor of a class.

These are the main difference between constants and readonly fields in C#. If I missed any other important points, let me know in the comments below.

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