怎么删除原有TXT文件中的记录或者把要输入的记录覆盖带原有的记录

Question

我把原来文档中的记录读出来后对其做完增删改后，再存回去会直接加在后面。。原有的记录还在。。我不想原有记录还存在，怎么把原有记录删除啊

Answer 1

还有怎么写hashtable的散列函数啊，是重载GetHashCode()这个方法么，如果我要用二次探查法，GetHashCode()的重载方法中该怎么写？

Answer 2

代码是这样的using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Collections;
namespace 学生信息管理系统
{
    class studentinfo
    {        public string Name;
        public int Id;
        public bool Sex;
        public int Age;
        public override string ToString()
        {
            return Id + " " + Name + " " + Sex + " " + Age;
        }
        static void menu()
        {
            Console.WriteLine("1.插入学生信息");
            Console.WriteLine("2.查看学生信息");
            Console.WriteLine("3.删除学生信息");
            Console.WriteLine("4.退出");
        }
        public void add()
        {
            Console.Write("请输入学号：");
            Id = Convert.ToInt32(Console.ReadLine());
            Console.Write("请输入名字：");
            Name = Console.ReadLine();
            Console.Write("请输入性别（true为男，女为false）：");
            Sex = Convert.ToBoolean(Console.ReadLine());
            Console.Write("请输入年龄：");
            Age = Convert.ToInt32(Console.ReadLine());
        }
        static void Main(string[] args)
        {
            int choice;
            string str="y";
            string s1 = null;
            string s2 = null;
            int a;
            int b;
            FileStream fs = new FileStream("stuinfo.txt",FileMode.OpenOrCreate,FileAccess.ReadWrite);
            StreamWriter w = new StreamWriter(fs);
            StreamReader sr = new StreamReader(fs);
            StreamReader r1 = new StreamReader(fs);
            StreamReader r2 = new StreamReader(fs);
            Hashtable h = new Hashtable(10);
            while ((s1 = r1.ReadLine()) != null)
            {
                a = Convert.ToInt32(s1[0] + "" + s1[1] + "" + s1[2] + "" + s1[3] + "" + s1[4] + "" + s1[5] + "" + s1[6] + "" + s1[7]);
                h.Add(a, s1);
            }
            while (true)
            {
                menu();
                Console.WriteLine("请选择操作编号：");
                choice = Convert.ToInt32(Console.ReadLine());
                switch (choice)
                {
                    case 1:
                        {                           
                            while (str=="y")
                            {
                                studentinfo stu = new studentinfo();
                                stu.add();
                                h.Add(stu.Id, stu);
                                Console.Write("还要继续插入么？y/n: ");
                                str=Console.ReadLine();
                            }
                        }
                        break;
                    case 2:
                        {
                            foreach (object value in h.Values)
                            {
                                Console.WriteLine(value.ToString());
                            }
                        }
                        break;
                    case 3:
                        {
                            while ((s2 = r1.ReadLine()) != null)
                            {
                                b = Convert.ToInt32(s2[0] + "" + s2[1] + "" + s2[2] + "" + s2[3] + "" + s2[4] + "" + s2[5] + "" + s2[6] + "" + s2[7]);
                                h.Add(b, s1);
                            }
                            Console.Write("请输入要删除的学生信息的学生学号：");
                            int key = Convert.ToInt32(Console.ReadLine());
                            h.Remove(key);
                        }
                        break;
                    case 4:
                        foreach (object value in h.Values)
                            {
                                w.WriteLine(value.ToString());
                            }
                            w.Close();
                        return;
                }
            }
        }
    }
}

Answer 3

FileStream.Seek(0, SeekOrigin.Begin)

Answer 4

新建一个文件名一样的Text文件存储，就会自动覆盖