Question

Whenever I tried to search about differences between classes and structs in C# or .net, I ended up with the conceptual overview of the two things like value type or the reference type, where the variables are allocated etc. But I need some practical differences. I have found some like different behavior of assignment operator, having constructors etc. Can anybody provide some more practical differences which will be directly useful while coding? Like the things works with one but not with other or same operation showing different behavior. And some common mistakes regarding these two.

Also please suggest where to consider using a struct instead of a class. And where the structs should not be used.

Edit:
Do I have to call the constructor explicitly or just declaring a struct type variable will suffice?(Should I make it a new question?)

Answer 1

OK, here are a few specific, practical differences:

• A variable can be null if it’s a class, but is never null if it’s a struct.

• default(T) is null for a class, but for a struct actually constructs a value (consisting of lots of binary zeros).

• A struct can be made nullable by using Nullable<T> or T?. A class cannot be used for the T in Nullable<T> or T?.

• A struct always has a public default constructor (a constructor with zero parameters). The programmer cannot override this constructor with a custom implementation — it is basically “set in stone”. A class allows the programmer to have no default constructor (or a private one).

• The fields in a class can have default values declared on them. In a struct they can’t.

• A class can inherit from another class, but a struct cannot be declared to derive from anything (it implicitly derives from System.ValueType).

• It makes sense to use a class in object.ReferenceEquals(), but using a struct variable will always yield false.

• It makes sense to use a class in a lock() statement, but using a struct variable will cause very subtle failure. The code will not be locked.

• On a 32-bit system, you can theoretically allocate an array of up to 536,870,912 references to a class, but for a struct you need to take the size of the struct into account because you are allocating actual instances.