[转贴] C++ 判断主机是否处于联网状态下

直接让本机访问一个网站，如果成功的话，就说明成功联网，没有访问成功，则说明没有联网！！！

#include<iostream>
#include <WINSOCK2.H>
#pragma comment(lib,"ws2_32.lib")
#define LEN 1024    //接收数据的大小
using namespace std;


int main()
{
    //加载套接字库
    WORD wVersionRequested;
    WSADATA wsaData;
    int err;

    wVersionRequested = MAKEWORD( 1, 1 );    //初始化Socket动态连接库,请求1.1版本的winsocket库

    err = WSAStartup( wVersionRequested, &wsaData );
    if ( err != 0 ) {
        return 0;
    }

    if ( LOBYTE( wsaData.wVersion ) != 1 ||   //判断请求的winsocket是不是1.1的版本
        HIBYTE( wsaData.wVersion ) != 1 ) {
        WSACleanup( );          //清盘
        return 0;                   //终止对winsocket使用
    }
    //WSADATA ws;
    //WSAStartup(MAKEWORD(2,2),&ws);//
    char http[60] = "www.google.com";           //访问谷歌网页
    SOCKET sock = socket(AF_INET,SOCK_STREAM,0);//建立socket
    if (sock == INVALID_SOCKET)
    {
        cout<<"建立访问socket套接字失败!"<<endl;
        return 0;
    }
    sockaddr_in hostadd;
    hostent* host = gethostbyname(http);//取得主机的IP地址
    if(host==NULL)
    {
        cout<<"主机处于没有联网状态;"<<endl;
        return 0;
    }
    cout<<"主机处于联网状态，现在可以进行通信!"<<endl;
    memcpy(&hostadd,host->h_addr,sizeof(hostadd));//将返回的IP信息Copy到地址结构
    hostadd.sin_family = AF_INET;
    hostadd.sin_port = htons(80);


    char buf[LEN]="GET / HTTP/1.1\r\nHost: ";//构造Http请求数据包
    strcat(buf,inet_ntoa(hostadd.sin_addr));
    strcat(buf," \r\nContent-Length: 10\r\n\r\n");
    strcat(buf,"Connection:close");


    int time = 1000;    //超时时间
    setsockopt(sock,SOL_SOCKET,SO_RCVTIMEO,(char*)&time,sizeof(time));


    if (connect(sock,(sockaddr*)&hostadd,sizeof(hostadd)) == SOCKET_ERROR)//连接请求
    {
        cout<<"与网页建立连接失败!"<<endl;
        return 0;
    }
    if (SOCKET_ERROR == send(sock,buf,strlen(buf)+1,0))//发送构造好的Http请求包
    {
        cout<<"发送数据包失败!"<<endl;
        return 0;
    }
    memset(buf,0,LEN);
    recv(sock,buf,LEN,0);               //接收返回的数据
    cout<<"从网页中获取的数据为:"<<buf;
    closesocket(sock);
    WSACleanup();
return 0;
}