C# Struct Instances vs. Class Instances

In this chapter you will learn:

What are the difference between struct and class
struct with value types and ref types

Struct vs Class

Classes are reference types. A variable of a class object holds a reference to the object. Two class variables may refer to the same object. Instances of classes are created by using the new operator.

In the following example, Person is the type and person1 and person2 are instances, or objects, of that type.


using System;/*from  ww w. jav  a 2  s . com*/

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }
    //Other properties, methods, events...
}

class Program
{
    static void Main()
    {
        Person person1 = new Person("Jack", 6);
        Console.WriteLine("person1 Name = {0} Age = {1}", person1.Name, person1.Age);

        // Declare  new person, assign person1 to it.
        Person person2 = person1;

        //Change the name of person2, and person1 also changes.
        person2.Name = "Tom";
        person2.Age = 16;

        Console.WriteLine("person2 Name = {0} Age = {1}", person2.Name, person2.Age);
        Console.WriteLine("person1 Name = {0} Age = {1}", person1.Name, person1.Age);

    }
}

The output:

Structs are value types. A variable of a struct object holds a copy of the entire object. Instances of structs can also be created by using the new operator, but this is not required.


using System;/*from   w  w  w. j  av a  2 s  .c  o m*/

public struct Person
{
    public string Name;
    public int Age;
    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }
}

public class Application
{
    static void Main()
    {
        // Create struct instance and initialize by using "new".
        Person p1 = new Person("Jack", 9);
        Console.WriteLine("p1 Name = {0} Age = {1}", p1.Name, p1.Age);

        // Create new struct object. 
        Person p2 = p1;

        // Assign values to p2 members.
        p2.Name = "Tom";
        p2.Age = 7;
        Console.WriteLine("p2 Name = {0} Age = {1}", p2.Name, p2.Age);

        // p1 values remain unchanged because p2 is  copy.
        Console.WriteLine("p1 Name = {0} Age = {1}", p1.Name, p1.Age);

    }
}

The output:

Example 2

struct with value types and ref types


using System;//from   w  w  w .j  a  v  a2s . c o m

class MyClass
{
  public string x;
  public MyClass(string s)  {
      x = s;
  }
}

struct MyStruct
{
  public MyClass refType;   // Ref type.
  public int valueType;     // Val type

  public MyStruct(string s)
  {
    refType = new MyClass(s);
    valueType = 9;
  }
}

class MainClass
{
  public static void Main(string[] args)
  {
    MyStruct valWithRef = new MyStruct("Initial value");
    valWithRef.valueType = 6;

    MyStruct valWithRef2;
    valWithRef2 = valWithRef;

    valWithRef2.refType.x = "I am NEW!";
    valWithRef2.valueType = 7;

    Console.WriteLine("Values after change:");
    Console.WriteLine("valWithRef.refType.x is {0}", valWithRef.refType.x);
    Console.WriteLine("valWithRef2.refType.x is {0}", valWithRef2.refType.x);
    Console.WriteLine("valWithRef.valueType is {0}", valWithRef.valueType);
    Console.WriteLine("valWithRef2.valueType is {0}", valWithRef2.valueType);
  }
}

The code above generates the following result.

Next chapter...

What you will learn in the next chapter:

Home »
  C# Tutorial »
    C# Types »
      C# Struct

C# Structs

C# Struct Instances vs. Class Instances

C# struct Constructor
C# struct equality
C# Generic struct