一個最基本的UDP通信代碼例子

小例子代碼實現了基於udp 的socket通信。完成的功能如下：

1、          利用socket編程建立服務器與客戶端之間的UDP連接。

2、          完成C/S之間的數據通信，具體包括4點：

        ①  Client通過給定的Server IP和端口號向Server端發送請求。請求來自cmd命令行用戶輸入。

        ② Server端保持監聽狀態，收到Client端請求後，將請求內容輸出到命令行。

        ③ Server端每接收一次請求數據，即向發出請求的客戶端發送“OK”字符串，表示該請求已經Received。

        ④ Client端接收到“OK”字符串後即將其輸出到命令行。

服務器端代碼如下：

//chang. exercise of UDP socket.
// Implements the function of send info between server and client.
//When this server is listening and a client send an request, it's will print the info on the cmd and reply a data:"OK".
//server.
#include "stdio.h"
#include "Winsock2.h"
#include "iostream"
#include "string"
//should add the under line if not add lib in the project.(appendicular dependent)
//#pragma comment(lib, "ws2_32.lib")

//define host IP and usable port.
#define HOST_IP 127.0.0.1
#define HOST_PORT 8080
#define OK_STR "OK"

void main(){
    //the version bit of Winsock
    int version_a = 1;//low bit
    int version_b = 1;//high bit

    //makeword
    WORD versionRequest = MAKEWORD(version_a,version_b);
    WSAData wsaData;
    int err;
    //wsa startup
    err = WSAStartup(versionRequest, &wsaData);

    if(err != 0 ){
        printf("ERROR!");
        return;
    }
    //check whether the version is 1.1, if not print the error and cleanup wsa?
    if (LOBYTE(wsaData.wVersion)  != 1 || HIBYTE(wsaData.wVersion) != 1)
    {
        printf("WRONG WINSOCK VERSION!");
        WSACleanup();
        return;
    }

    /*
    *build the socket
    *first param is protocol family, generally AF_INET for IP internet.
    *second param is type of socket, SOCK_DGRAM is for Data Gram（UDP）, and SOCK_STREAM is for TCP.
    *the last param is communicate protocol. Generally is zero.
    */
    SOCKET socServer = socket(AF_INET, SOCK_DGRAM,0);
    //infomation of address, always NOT being operated directly.
    SOCKADDR_IN addr_Srv;
    //Struct sin_addr is  used to defind IP address,  it's a property of addr_in.
    //It's nest three structs as S_un_b, S_un_w and S-un.(union)
    addr_Srv.sin_addr.S_un.S_addr = htonl(INADDR_ANY);
    //set protocol family
    addr_Srv.sin_family = AF_INET;
    //set host port
    addr_Srv.sin_port = htons(HOST_PORT);

    //bind socket to  the host
    bind(socServer,( SOCKADDR*) &addr_Srv, sizeof(SOCKADDR));

    //address  of a client
    SOCKADDR_IN addr_Clt;
    char recvBuf[100];

    int fromlen = sizeof(SOCKADDR);
    // while() to listen all the time
    while(true){
        //receive data function of server
        recvfrom(socServer, recvBuf, 100, 0,  (SOCKADDR*) &addr_Clt, &fromlen);
        //output the data received to cmd
        std::cout<<recvBuf<<std::endl;
        //send "OK" to the from_client to indicates that data have been received.
        //send function is used by server, while sendto function is used by client. NOT sure.
//      send(addr_Clt, OK_STR,  strlen(OK_STR)+1, 0);
        sendto(socServer, OK_STR, strlen(OK_STR)+1, 0, (SOCKADDR*)&addr_Clt, sizeof(SOCKADDR));
    }

    // at last close the socket.
    closesocket(socServer);
    //cleanup WSAData
    WSACleanup();}

客戶端代碼如下：

//chang. exercise of UDP socket.
// Implements the function of send info between server and client.
//When this server is listening and a client send an request, it's will print the info on the cmd and reply a data:"OK".
//client.
#include "Winsock2.h"
#include "iostream"
#include "stdio.h"
#pragma comment(lib, "ws2_32.lib")


#define HOST_IP "127.0.0.1"
#define HOST_PORT 8080

void main(){
    //the version bit of Winsock
    int version_a = 1;//low bit
    int version_b = 1;//high bit

    //makeword
    WORD versionRequest = MAKEWORD(version_a,version_b);
    WSAData wsaData;
    int error;
    error = WSAStartup(versionRequest, &wsaData);

    if(error != 0   ){
        printf("ERROR!");
        return;
    }
    //check whether the version is 1.1, if not print the error and cleanup wsa?
    if (LOBYTE(wsaData.wVersion)  != 1 || HIBYTE(wsaData.wVersion) != 1)
    {
        printf("WRONG WINSOCK VERSION!");
        WSACleanup();
        return;
    }


    //request info obtained by user's input
    char requestStr[100];

    //build a sockeet
    SOCKET socClient = socket(AF_INET, SOCK_DGRAM, 0);
    SOCKADDR_IN addrSrv;        // a instance of SOCKADDR_IN, which is used in format of SOCKADDR.
    addrSrv.sin_addr.S_un.S_addr=inet_addr("127.0.0.1");        //set the host IP
    addrSrv.sin_family=AF_INET;     //set the protocol family
    addrSrv.sin_port=htons(HOST_PORT);      //set the port number

    // array to store the data that server feedback.
    char cRecvBuf[100];
//  int len=sizeof(SOCKADDR);

    //while
    while(true){
            // gain info that user input
        std::cin>>requestStr;
        //sendto function is used to send programe data to the server
        sendto(socClient, requestStr, strlen(requestStr)+1, 0, (SOCKADDR*) &addrSrv, sizeof(SOCKADDR));

        //receive the feedback info from server
        //recv function is used in client.
        recv(socClient, cRecvBuf, strlen(cRecvBuf)+1, 0);
        //output the cRecvBuf to cmd
        std::cout<< cRecvBuf << std::endl;
    }

    //close the socket and cleanup the wsadata
    closesocket(socClient);
    WSACleanup();

//  return 0;
}