C#编程和网络编程

一、C#简单helloworld程序

1.用C#编写一个命令行/控制台hello world程序，实现如下功能：在屏幕上连续输出50行“hello cqjtu！重交物联2018级”；

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

namespace helloworld控制台
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 0; i < 50; i++)
            {
                Console.WriteLine("hello cqjtu!重交物联2018级");
            }
            Console.ReadKey();
        }
    }
}

2.创建一个server服务器和client进行通信编程

服务器代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Sockets;
using System.Net;

namespace server
{
    class Program
    {
        static void Main(string[] args)
        {
            UdpClient udpRec = new UdpClient(8888);
            Console.WriteLine("服务器已开启！");
            try
            {
                while (true)
                {
                    IPEndPoint remoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);
                    byte[] recBytes = udpRec.Receive(ref remoteIpEndPoint);
                    string returnData = Encoding.Default.GetString(recBytes);
                    Console.WriteLine("接收到的数据是:" + returnData);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }
            finally
            {
                udpRec.Close();
            }
        }
    }
}

客户端代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Sockets;
using System.Net;


namespace client
{
    class Program
    {
        static void Main(string[] args)
        {
            int j = 0;
            while (j < 50)
            {
                Console.WriteLine("hello cqjtu!重交物联2018级");
                j++;
            }
            UdpClient client = new UdpClient("127.0.0.1", 8888);
            Console.WriteLine("正在准备发送数据！");
            try
            {
                while (j>0)
                {
                    string str = "hello cqjtu!重交物联2018级";
                    byte[] sendBytes = Encoding.Default.GetBytes(str);
                    client.Send(sendBytes, sendBytes.Length);
                    j--;  
                }
            }
           
            catch (Exception e)
            {
                
                Console.WriteLine(e);
            }
            finally
            {
                client.Close();
            }
            Console.WriteLine("数据发送成功！");
            Console.Read();
        }
    }
}

二、写一个Form窗口程序

用VS2015/2017 的C#编写一个简单的Form窗口程序，有一个文本框 textEdit和一个发送按钮button，运行程序后，可以在文本框里输入文字，如“hello cqjtu物联18!”，点击button，将这些文字发送给室友电脑或树莓派，采用UDP套接字；

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;
using System.Threading;


namespace Server
{
    public partial class Form1 : Form
    {
        private UdpClient receiveUdpClient;//接收用
        private UdpClient sendUdpClient;//发送用
        private const int port = 8888;//和本机绑定的端口号
        IPAddress ip;//本机ip
        IPAddress remoteip;//=IPAddress.Parse("");远程主机ip
        public Form1()
        {
            InitializeComponent();
            CheckForIllegalCrossThreadCalls = false;
            //获取本机可用IP地址
            IPAddress[] ips = Dns.GetHostAddresses(Dns.GetHostName());
            foreach (IPAddress ipa in ips)
            {
                if (ipa.AddressFamily == AddressFamily.InterNetwork)
                {
                    ip = ipa;
                    break;
                }
            }
            //为了在同一台机器调试，此IP也作为默认远程IP
             remoteip = ip;

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //创建一个线程接收远程主机发来的信息
            Thread myThread = new Thread(ReceiveData);
            myThread.IsBackground = true;
            myThread.Start();
        }

        //接收数据
        private void ReceiveData()
        {
            IPEndPoint local = new IPEndPoint(ip, port);
            receiveUdpClient = new UdpClient(local);
            IPEndPoint remote = new IPEndPoint(IPAddress.Any, 0);
            while (true)
            {
                try
                {
                    //关闭udpClient 时此句会产生异常
                    byte[] receiveBytes = receiveUdpClient.Receive(ref remote);
                    string receiveMessage = Encoding.Unicode.GetString(
                        receiveBytes, 0, receiveBytes.Length);
                    listBox1.Items.Add("收到的消息:" + receiveMessage);
                }
                catch
                {
                    break;
                }
            }
        }
        //点击发送按钮发送数据
        private void button1_Click(object sender, EventArgs e)
        {
            //remoteip = IPAddress.Parse(txt_IPAddress.Text);
            Thread myThread = new Thread(SendMessage);
            myThread.IsBackground = true;
            myThread.Start(textBox2.Text);
        }
        //发送消息
        private void SendMessage(object obj)
        {
            string message = (string)obj;
            sendUdpClient = new UdpClient(0);
            byte[] bytes = Encoding.Unicode.GetBytes(message);
            IPEndPoint iep = new IPEndPoint(remoteip, port);
            try
            {
                sendUdpClient.Send(bytes, bytes.Length, iep);
                listBox1.Items.Add("发送的消息:" + message);
                textBox2.Clear();
            }
            catch (Exception ex)
            {
                listBox1.Items.Add("发送出错:" + ex.Message);
            }
        }
        delegate void AddItemDelegate(ListBox listbox, string text);
        private void AddItem(ListBox listbox, string text)
        {
            if (listbox.InvokeRequired)
            {
                AddItemDelegate d = AddItem;
                //Control.Invoke 方法 (Delegate, Object[]):
                //在拥有控件的基础窗口句柄的线程上，用指定的参数列表执行指定委托。
                listbox.Invoke(d, new object[] { listbox, text });
            }
            else
            {
                //Add：动态的添加列表框中的项
                listbox.Items.Add(text);

                //SelectedIndex属性获取单项选择ListBox中当前选定项的位置
                //Count：列表框中条目的总数
                listbox.SelectedIndex = listbox.Items.Count - 1;

                //调用此方法等效于将 SelectedIndex 属性设置为-1。 
                //可以使用此方法快速取消选择列表中的所有项。
                listbox.ClearSelected();
            }
        }
        delegate void ClearTextBoxDelegate();
        private void ClearTextBox()
        {
            if (textBox2.InvokeRequired)
            {
                ClearTextBoxDelegate d = ClearTextBox;
                textBox2.Invoke(d);
            }
            else
            {
                textBox2.Clear();
                textBox2.Focus();
            }
        }

        private void label2_Click(object sender, EventArgs e)
        {

        }

        private void label2_Click_1(object sender, EventArgs e)
        {

        }
    }
}

三、wirshark

安装wireshark 抓包软件，抓取上述程序发送的网络包，对数据帧结构进行分析
前四行分别为源端口，目的端口，长度，校验和。
每一个各占2byte，一共8byte。
发送的消息为：“你好，重庆交通大学”，一共9个字符，18byte，18+8=26，即长度。