readonly

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class C1
    {
        public readonly  int myvalue=1;
        public readonly static  int  value = 2;
        public C1()
        { myvalue = 3; 
            //value = 4;//无法对静态只读字段赋值(静态构造函数或变量初始值中除外)

        }
        static  C1()
        {
            //myvalue = 3;//非静态的字段、方法或属性“ConsoleApplication1.C1.myvalue”要求对象引用

            value = 4;

        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            C1 C = new C1();
            Console.WriteLine("myvalue:{0}", C.myvalue);
            //C.myvalue = 20;//无法对只读的字段赋值(构造函数或变量初始值指定项中除外)
            //C1.value = 20;//无法对只读的字段赋值(构造函数或变量初始值指定项中除外)
            Console.WriteLine("value:{0}", C1.value);
            Console.ReadLine();

        }
    }
}
//const字段只能在编译的时候决定，也就是说只能在字段声明的语句中初始化。而readonly字段可以在静态构造函数中完成的！
//readonly字段的值只能在字段的声明语句中和类的任何构造函数中设置