在没有任何数据时进行无效的读取尝试

Question

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            SqlConnection conn = new SqlConnection(@"Server=LEON\MATER;database=test;Uid=sa;Pwd=sa");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                Console.Write("连接成功！");            }
            else
                Console.Write("连接失败！");
            //while (true)
            //{
                        using (SqlCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = "SELECT * FROM dbo.qwe";
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    Console.WriteLine("请输入用户名！");
                    string name = Console.ReadLine();
                    if (name == reader.GetString(reader.GetOrdinal("name")))
                    {
                        Console.WriteLine("请输入密码！");
                        string password = Console.ReadLine();
                        if (password == reader.GetString(reader.GetOrdinal("password")))
                        {
                            Console.WriteLine("欢迎进入系统！");
                        }
                        else
                        {
                            Console.WriteLine("密码错误！");
                        }                    }
                    else
                    {
                        Console.WriteLine("用户名不存在！");
                    }
                }                //}
            }            Console.ReadLine();
            Console.WriteLine("good");        }
    }
}在下面这句出错
 using (SqlDataReader reader = cmd.ExecuteReader())

Answer 1

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            SqlConnection conn = new SqlConnection(@"Server=LEON\MATER;database=test;Uid=sa;Pwd=sa");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                Console.Write("连接成功！");            }
            else
                Console.Write("连接失败！");
            //while (true)
            //{
                        using (SqlCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = "SELECT * FROM dbo.qwe";
                cmd.Connection = conn;  //缺少这一句
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    Console.WriteLine("请输入用户名！");
                    string name = Console.ReadLine();
                    if (name == reader.GetString(reader.GetOrdinal("name")))
                    {
                        Console.WriteLine("请输入密码！");
                        string password = Console.ReadLine();
                        if (password == reader.GetString(reader.GetOrdinal("password")))
                        {
                            Console.WriteLine("欢迎进入系统！");
                        }
                        else
                        {
                            Console.WriteLine("密码错误！");
                        }                    }
                    else
                    {
                        Console.WriteLine("用户名不存在！");
                    }
                }                //}
            }            Console.ReadLine();
            Console.WriteLine("good");        }
    }
}

Answer 2

using (SqlDataReader reader = cmd.ExecuteReader())
  {
reader.Read();

Answer 3

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            using (SqlConnection conn = new SqlConnection(@"Server=LEON\MATER;database=test;Uid=sa;Pwd=sa"))
            {
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                Console.Write("连接成功！");            }
            else
                Console.Write("连接失败！");
            //while (true)
            //{            Console.WriteLine("请输入用户名！");
            string name = Console.ReadLine();
           
            using (SqlCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = "SELECT * FROM dbo.qwe ";
                
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    reader.Read();
                    if (name == reader.GetString(reader.GetOrdinal("name")))
                    {
                        Console.WriteLine("请输入密码！");
                        string password = Console.ReadLine();
                        if (password == reader.GetString(reader.GetOrdinal("password")))
                        {
                            Console.WriteLine("欢迎进入系统！");
                        }
                        else
                        {
                            Console.WriteLine("密码错误！");
                        }                    }
                    else
                    {
                        Console.WriteLine("用户名不存在！");
                    }
                }                }
            }            Console.ReadLine();
            Console.WriteLine("good");        }
    }
}除了要加reader.Read();密码的输入也出了问题，不过我把密码在数据库的数据类型改为nvarchar就好了最后说一下read，这个只有在执行后才会读数

Answer 4

using等同于while循环
可以在using之前对ExecuteReader（）的返回数进行判断，是否大于零。