#include"winsock2.h"

 #include<iostream>

 using namespace std;

 //This line is very important

 #pragma comment(lib,"ws2_32.lib")

 int main()

 {

     WSADATA              wsaData;

     SOCKET               ReceivingSocket;

     SOCKADDR_IN          ReceiverAddr;

     int                  Port = ;

     char                 ReceiveBuf[];

     int                  BufLength = ;

     SOCKADDR_IN          SenderAddr;

     int                  SenderAddrSize = sizeof(SenderAddr);

     int                  Ret;

     if ((Ret = WSAStartup(MAKEWORD(,), &wsaData)) != )

     {

         cout<<"WSAStartup failed with error "<<Ret<<endl;

         //here no WSACleanup，because we do not create anything;

         return -;

     }

     // Create a new socket to listening for client connections.

     //Note the difference with TCP

     ReceivingSocket = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);

     if ( INVALID_SOCKET == ReceivingSocket)

     {

         cout<<"Socket failed with error "<<WSAGetLastError()<<endl;

         WSACleanup();

         return -;

     }

     ReceiverAddr.sin_family = AF_INET;

     ReceiverAddr.sin_addr.s_addr = htonl(INADDR_ANY);

     ReceiverAddr.sin_port = htons(Port);

     //to bind

     if (bind(ReceivingSocket, (SOCKADDR *)&ReceiverAddr, sizeof(ReceiverAddr)) == SOCKET_ERROR)

     {

         cout<<"Binding failed with error "<<WSAGetLastError()<<endl;

         closesocket(ReceivingSocket);

         WSACleanup();

         return -;

     }

     // Listen for client connections. We used a backlog of 5 which is

     // normal for many applications.

     cout<<"** We are ready to receive 1 datagram from any interface on port "<<Port<<"**"<<endl;

     //accep a connection when one arrives

     cout<<"** We are waiting for data...**\n";

     //SenderAddrSize = sizeof(SenderAddr);

     Ret = recvfrom(ReceivingSocket,ReceiveBuf,BufLength,,(SOCKADDR *)&SenderAddr,&SenderAddrSize);

     if (SOCKET_ERROR == Ret)

     {

         cout<<"Recvfrom failed with error "<<WSAGetLastError()<<endl;

         closesocket(ReceivingSocket);

         WSACleanup();

         return -;

     }

     cout<<"**We have successfully recieve "<<Ret<<" Byte(s) data!**\n";

     cout<<"**We are going to close the client connection...**\n";

     closesocket(ReceivingSocket);

     WSACleanup();

     return ;

 }

 #include"winsock2.h"

 #include<iostream>

  #include <time.h>

 using namespace std;

 //This line is very important

 #pragma comment(lib,"ws2_32.lib")

 int main(int argc, char **argv)

 {

     WSADATA              wsaData;

     SOCKET               SendingSocket;

     SOCKADDR_IN          ReceiverAddr;

     int                  Port = ;

     int                  Ret;

     if (argc <= )

     {

         cout<<"USAGE: udpclient <Server IP address>.\n";

         return -;

     }

     // Initialize Winsock version 2.2

     if ((Ret = WSAStartup(MAKEWORD(,), &wsaData)) != )

     {

         cout<<"WSAStartup failed with error "<<Ret<<endl;

         return -;

     }

     // Create a new socket to make a client connection.

     SendingSocket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);//Note the difference with TCP

     if (INVALID_SOCKET == SendingSocket)

     {

         cout << "socket failed with error " << WSAGetLastError()<<endl;

         WSACleanup();

         return -;

     }

     ReceiverAddr.sin_family = AF_INET;

     ReceiverAddr.sin_port = htons(Port);

     ReceiverAddr.sin_addr.s_addr = inet_addr(argv[]);

     // Make a connection to the server with socket s.

     cout<< "We are trying to connect to " << inet_ntoa(ReceiverAddr.sin_addr)

         << ":" << htons(ReceiverAddr.sin_port) << "...\n";

     cout << "We will now try to send a hello message.\n";

     if ((Ret = sendto(SendingSocket, "Hello", , , (SOCKADDR *)&ReceiverAddr,sizeof(ReceiverAddr))) == SOCKET_ERROR)

     {

         cout << "Sendto failed with error " << WSAGetLastError()<<endl;

         closesocket(SendingSocket);

         WSACleanup();

         return -;

     }

     cout << "We successfully sent " << Ret << " byte(s).\n";

     // When you are finished sending and receiving data on socket s,

     // you should close the socket.

     cout << "We are closing the connection.\n";

     closesocket(SendingSocket);

     // When your application is finished handling the connection, call

     // WSACleanup.

     WSACleanup();

     return ;

 }