What is the difference between `Fields` and `Properties` in C#?

Question

Edit, as per these comments:

Do you mean "Property" vs "Field"? public String S1; vs public String S2 { get; set; } – dana

Exactly dana, i mean the same. – Asad

Asad: you really need to try to use some other term to describe what you mean so that we can better understand your question. C# does not have global variables. The fields you can define in C# are not global - they are members of the class type. – dthorpe

Hi fellas,

Need your expert views over the difference between Field and Property. As in my project, I have used certain global variables which later on i changed to 'Properties' . My manager is asking what is the benefit of using Properties of variables instead of Fields.

Although I have replied him that Property provides a kind of secure/safe/indirect access to Field instead of modifying them directly if they are declared public or protected. But Please provide me with some more convincing arguments.

Thanks and Regards

@Asad: You should get your terminology right: Fields are not Global Variables, C# does not have global variables (as a few commenters mentioned: you can simulate global variables, but you should not do that).

Answer 1

The main advantage is that you can attach all sorts of functionality to a property such as validation, synchronization etc. You can't do that for a class field. For example, a field can throw BCL exceptions on assignment but it can't throw an exception that make sense with logic in your problem domain.

Also imagine trying to protect a field for thread synchronization. You have to write extra code in all the places in your code where the field is accessed. To do that with a property you can simply wrap the getter and setter with a lock in one place. (But beware! The ease of using lock in property getters and setters can give you a false sense of security if you're working with mutable types. See the accepted answer in this post.)

Now, you might think that validation and synchronization are not important to you for this particular value, and they may never be for this particular instance. But by using properties instead of direct field access is making your application much more maintainable in the future. (Suppose the value of an integer field suddenly needs to come from a source different from the original implementation and it needs to be converted from a string to an int. If you use properties to wrap the field then you make the change in one place and all the client code that uses that property does not need to change at all!)

Also, for managing information shared across many classes (global) take a look at the singleton pattern. But beware! Even though it looks neat and clean you can still get into trouble with it. Though if you really need global data you should use properties contained in a singleton. If nothing else, it's a good organization strategy.

To avoid issues with singletons or "global" data take a look at dependency injection as a much better alternative.

Answer 2

C# syntax doesn't have a "global variable" declaration. It has properties and fields, and static properties and fields.

If by "global variable" you mean a static field or static property, that is different from a property or field in that the static field or property is not stored in the object instance data, it is stored in global memory. The value assigned to a static field or property is accessible to all instances of that class, and all instances see the same value. A static field is the closest thing C# has to the notion of "global variable" found in other programming languages.

A non-static property or field stores its data in the object instance data, so each instance of the object has its own local copy. Modifying object1.A property will not affect the value of object2.A property.

Answer 3

Have a look at Properties (C# Programming Guide)

A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field. Properties can be used as if they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily and still helps promote the safety and flexibility of methods.

• Properties enable a class to expose a public way of getting and setting values, while hiding implementation or verification code.
• A get property accessor is used to return the property value, and a set accessor is used to assign a new value. These accessors can have different access levels.
• Properties that do not implement a set accessor are read only.

Answer 4

I prefer properties because then when I use them in code I know exactly which class was used to call them (ex. class.property = value). Public class variables can become a real pain and waste of time when you are trying to figure out where they came from during debugging.