Comparision between Structures and Classes

Structures and Class Differences:
1.Classes are reference types and structs are value types.
Since classes are reference type, a class variable can be assigned null.But we cannot assign null to a struct variable, since structs are value type.

Example:

namespace SampleStruct { struct Test { public int add(int a, int b) { return a + b; } public void Display() { Console.WriteLine("Hi from Structure Declaration"); Console.ReadLine(); } } class Program { static void Main(string[] args) { Program p = null; //No Error Test t = null;//Error Occurred(Cannot convert null to ‘SampleStruct.Test’because it is a value type) } } }

2. When you instantiate a class, it will be allocated on the heap.When you instantiate a struct, it gets created on the stack.

3. You will always be dealing with reference to an object ( instance ) of a class. But you will not be dealing with references to an instance of a struct ( but dealing directly with them ).

4. When passing a class to a method, it is passed by reference. When passing a struct to a method, it's passed by value instead of as a reference.

5. You cannot have instance Field initializers in structs.But classes can have initializers.

Example:

namespace ConsoleApplication9 { class Program { int y = 34; public void Show() { Console.WriteLine("Hi from Structure"); Console.ReadLine(); } static void Main(string[] args) { Test t; t.Show(); } } struct Test { int x = 10;//Error: 'ConsoleApplication9.Test.x': cannot have instance field initializers in structs public void Show() { Console.WriteLine("Hello from structure"); Console.ReadLine(); } } }

6. Classes can have explicit parameterless constructors. But structs cannot have explicit parameterless constructors.

Example:

namespace ConsoleApplication9 { class Program { int y = 34; public Program()// No Error { Console.WriteLine("Class Constructor"); Console.ReadLine(); } public void Show() { Console.WriteLine("Hi from Structure"); Console.ReadLine(); } static void Main(string[] args) { Program pgm = new Program(); Test t; t.Show(); } } struct Test { //int x = 10; public void Show() { Console.WriteLine("Hello from structure"); Console.ReadLine(); } public Test()//Error: Structs cannot contain explicit parameterless constructors { Console.WriteLine("Structure Destructor"); Console.ReadLine(); } } }

7. Classes must be instantiated using the new operator. But structs can be instantiated without using the new operator.

Example:

namespace ConsoleApplication9 { class Program { int y = 34; public Program() { Console.WriteLine("Class Constructor"); Console.ReadLine(); } public void Show() { Console.WriteLine("Hi from Structure"); Console.ReadLine(); } static void Main(string[] args) { Program pgm; pgm.Show();//Error: Use of unassigned local variable 'pgm' Test t; t.Show(); } } struct Test { public void Show() { Console.WriteLine("Hello from structure"); Console.ReadLine(); } } }

8. Classes support inheritance.But there is no inheritance for structs.( structs don't support inheritance polymorphism ). So we cannot have a base structure and a derived structure.

Example:

namespace ConsoleApplication9 { class Program:Test//Error: 'ConsoleApplication9.Program': cannot derive from sealed type { int y = 34; public Program() { Console.WriteLine("Class Constructor"); Console.ReadLine(); } public void Show() { Console.WriteLine("Hi from Structure"); Console.ReadLine(); } static void Main(string[] args) { Test t; t.Show(); } } struct Test:Program//Error: Type 'Program' in interface list is not an interface { public void Show() { Console.WriteLine("Hello from structure"); Console.ReadLine(); } } }

Note : Like classes, structures can implement interfaces

9. Since struct does not support inheritance, access modifier of a member of a struct cannot be protected or protected internal.

10. It is not mandatory to initialize all Fields inside the constructor of a class.But all the Fields of a struct must be fully initialized inside the constructor.

Example:

namespace ConsoleApplication9 { class Program { int y; public Program(int y) { Console.WriteLine("Class Constructor"); Console.ReadLine(); } public void Show() { Console.WriteLine("Hi from Structure"); Console.ReadLine(); } static void Main(string[] args) { } } struct Test { int a; public Test(int a)//Error: Field 'ConsoleApplication9.Test.a' must be fully assigned before control leaves the constructor { } public void Show() { Console.WriteLine("Hello from structure"); Console.ReadLine(); } } }

11. A class is permitted to declare a destructor.But a struct is not permitted to declare a destructor.

12. classes are used for complex and large set data. structs are simple to use.
structs are useful whenever you need a type that will be used often and is mostly just a piece of data.

13. The modifiers namely abstract and sealed are not permitted in struct. But it is permitted in class.