----------------------------------------------主程序

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication4{    class Program    {        static void Main(string[] args)        {            //自定义格式化字符串            Voctor v = new Voctor(3d, 4d, 5d);            Console.WriteLine("{0:zhang}", v);//Zhang:(3,4,5)            Console.WriteLine("{0:liu}", v);//Liu:(3,4,5)            Console.ReadKey();        }    }}

----------------------------------------------Voctor.cs

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ConsoleApplication4{    //自定义格式化字符串类或结构必须实现IFormattable接口    public class Voctor : IFormattable    {        double x, y, z;        public Voctor(double d1, double d2, double d3)        {            this.x = d1;            this.y = d2;            this.z = d3;        }        //format表示传递的说明符，例如N(不用考虑formatProvider)        public string ToString(string format, IFormatProvider formatProvider)        {            if (format == null)            {                return ToString();            }            //不区分大小写            string formatUpper = format.ToUpper();            switch (formatUpper)            {                case "ZHANG":                    return "Zhang:" + ToString();                case "LIU":                    return "Liu:" + ToString();                default:                    return ToString();            }        }        public override string ToString()        {            return string.Format("({0},{1},{2})", x, y, z);        }    }}