C# 类与结构的区别
类与结构的区别
C++中结构与类的唯一区别是在于默认的访问级别，但是C#中的区别就稍微多了点，C#中如下
(1)类是引用类型，结构是值类型。
类中：

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }
}


class Program
{
    static void Main()
    {
        Person person1 = new Person("Leopold", 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 = "Molly";
        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);


        // Keep the console open in debug mode.
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();


    }
}

    Output:
    person1 Name = Leopold Age = 6
    person2 Name = Molly Age = 16
    person1 Name = Molly Age = 16

结构中：

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".
        // Memory is allocated on thread stack.
        Person p1 = new Person("Alex", 9);
        Console.WriteLine("p1 Name = {0} Age = {1}", p1.Name, p1.Age);


        // Create  new struct object. Note that  struct can be initialized
        // without using "new".
        Person p2 = p1;


        // Assign values to p2 members.
        p2.Name = "Spencer";
        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);


        // Keep the console open in debug mode.
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey();
    }
}

  Output:
    p1 Name = Alex Age = 9
    p2 Name = Spencer Age = 7
    p1 Name = Alex Age = 9
(2)结构中可以包含构造函数，但是构造函数必须对全部字段赋值，因此结构没有默认构造函数
(3)结构不能被继承，但是结构可以实现接口
(4)结构直接继承自 System.ValueType，类继承自 System.Object
(5)结构中除非是const或者static变量，或者不能直接对变量初始化

namespace ConsoleApplication5
{
    struct struct1
    {
        //int x = 10;		//error
        int x;
        string str;


        //struct1(){}		//error


        //struct1(int _x)	//error
        //{ x = _x; }


        struct1(int _x, string _str)
        {
            x = _x;
            str = _str;
        }


        const int y = 10;	//OK
        static int z = 100;	//OK
    }
}

(6)结构可以是Nullable类型
所谓的Nullable类型就是System.Nullable<T>的实例，它的取值范围是值类型T可以表达的所有有效值 外加一个null值。
Nullable存在的意义：值类型必须初始化后才能使用，为了让值类型不用初始化，就诞生了这个类型了。