C#重定向输入输出

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {;
            StreamReader Reader;
            TextReader OldIn = Console.In;
            try
            {
                FileStream fs = new FileStream("./read.txt", FileMode.Open);
                Reader = new StreamReader(fs, Encoding.Default);
            }
            catch (Exception e)
            {
                Console.WriteLine("Cannot open read.txt for writing");
                Console.WriteLine(e.Message);
                return;
            }
            Console.SetIn(Reader);
            string a;
            a = Console.ReadLine();
        }
    }
}