udp广播

#include <iostream>
#include <WinSock2.h>
#include <stdio.h>
#include <iostream>
using namespace std;
#pragma comment(lib, "ws2_32.lib")
const int MAX_BUF_LEN = 255;
#pragma package(smart_init)
#pragma resource "*.dfm"


class CInitSock
{
public:
    CInitSock(BYTE minorVer = 2, BYTE major = 2)      //载入Winsock库
    {
        WSADATA wsaData;
        WORD sockVersion = MAKEWORD(minorVer, major);
        if (::WSAStartup(sockVersion, &wsaData) != 0)
        {
            return;
        }
    }
    ~CInitSock()
    {
        ::WSACleanup(); //释放Winsock库
    }
};


String GetIpAddress()
{


    char cHost[256] = { 0 };
    ::gethostname(cHost, 256);  //取得本地主机名
    hostent* pHost = ::gethostbyname(cHost);    //通过主机名得到地址信息

    //打印本机Ip地址
    in_addr addr;
    char* p = pHost->h_addr_list[0];
    if (p == NULL)
    {
        return "";
    }
    memcpy(&addr.S_un.S_addr, p, pHost->h_length);
    char* cIp = ::inet_ntoa(addr);
    cout << "本机IP:" << cIp << endl;
    String s = cIp;
    return s;
}
void broadcast_ip(String s)
{
      // 创建socket
    SOCKET connect_socket;
    connect_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (INVALID_SOCKET == connect_socket)
    {
        int err = WSAGetLastError();
        printf("socket  error! error code is %d/n", err);
        return ;
    }

    SOCKADDR_IN sin;
    sin.sin_family = AF_INET;
    sin.sin_port = htons(3779);
    sin.sin_addr.s_addr = INADDR_BROADCAST;

    bool bOpt = true;
    //设置该套接字为广播类型
    setsockopt(connect_socket, SOL_SOCKET, SO_BROADCAST, (char*)&bOpt, sizeof(bOpt));

    int nAddrLen = sizeof(SOCKADDR);

    char buff[MAX_BUF_LEN] = "";
    int nLoop = 0;
    while (1)
    {
        nLoop++;
        sprintf(buff, "%s", s.c_str());

        // 发送数据
        int nSendSize = sendto(connect_socket, buff, strlen(buff), 0, (SOCKADDR*)&sin, nAddrLen);
        if (SOCKET_ERROR == nSendSize)
        {
            int err = WSAGetLastError();
            printf("sendto  error!, error code is %d/n", err);
            return ;
        }
        printf("Send: %s/n", buff);
        Sleep(500);
    }
}

int get_serverip()
{
  

    // 创建socket
    SOCKET connect_socket;
    connect_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (INVALID_SOCKET == connect_socket)
    {
        err = WSAGetLastError();
        printf("socket error! error code is %d/n", err);
        return -1;
    }

    // 用来绑定套接字
    SOCKADDR_IN sin;
    sin.sin_family = AF_INET;
    sin.sin_port = htons(3779);
    sin.sin_addr.s_addr = 0;

    // 用来从网络上的广播地址接收数据
    SOCKADDR_IN sin_from;
    sin_from.sin_family = AF_INET;
    sin_from.sin_port = htons(3779);
    sin_from.sin_addr.s_addr = INADDR_BROADCAST;

    //设置该套接字为广播类型，
    bool bOpt = true;
    setsockopt(connect_socket, SOL_SOCKET, SO_BROADCAST, (char*)&bOpt, sizeof(bOpt));

    
　　

struct timeval tv_out;
         tv_out.tv_sec = 1000;//等待1秒
         tv_out.tv_usec = 0;
setsockopt(

connect_socket

,SOL_SOCKET,SO_RCVTIMEO,&tv_out, sizeof(tv_out));

// 绑定套接字
    err = bind(connect_socket, (SOCKADDR*)&sin, sizeof(SOCKADDR));
    if (SOCKET_ERROR == err)
    {
        err = WSAGetLastError();
        printf("bind  error! error code is %d/n", err);
        return -1;
    }

    int nAddrLen = sizeof(SOCKADDR);
    char buff[MAX_BUF_LEN] = "";
    int nLoop = 0;
         while (1)
    {
        // 接收数据
        int nSendSize = recvfrom(connect_socket, buff, MAX_BUF_LEN, 0, (SOCKADDR*)&sin_from, &nAddrLen);
        if (SOCKET_ERROR == nSendSize)
        {
            err = WSAGetLastError();
            printf("recvfrom error! error code is %d/n", err);
            return -1;
        }
        buff[nSendSize] = '\0';
                String s = buff;
        ShowMessage(s);
                break;
    }
}

线程函数

DWORD WINAPI ThreadFunc(LPVOID lpParam)
{
  CInitSock intSock;
  if(get_serverip()!="")
{
ShowMessage("在局域网里面已存在服务器");
}    
broadcast_ip(GetIpAddress());
} 

 

工程测试代码

// 启动服务器
//初始化Winsock库
    CInitSock initSock;


    //打印本机Ip地址
    String s = GetIpAddress();
        broadcast_ip(s);


// 客户端
CInitSock initSock;
get_serverip();


void __fastcall TForm1::FormCreate(TObject *Sender)

//初始化Winsock库
    CInitSock initSock;


    //打印本机Ip地址
    String s = GetIpAddress();
if(s!=""){
// 不能启动服务器
}