socket连接超时判断

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select 方式

判断m_server的m_port端口是否可以连上，超时限制为nTimeOut秒

BOOL ConnectTest(char * m_server,int m_port)
{

        struct hostent* host = NULL;
        struct sockaddr_in saddr;
        unsigned int s = 0;
        BOOL  ret;
        time_t start;
        int error;
        host = gethostbyname (m_server);
        if (host==NULL)return  FALSE;

        saddr.sin_family = AF_INET;
        saddr.sin_port = htons(m_port);
        saddr.sin_addr = *((struct in_addr*)host->h_addr);

        if( (s=socket(AF_INET, SOCK_STREAM, 0))<0){
                return FALSE;
        }

        fcntl(s,F_SETFL, O_NONBLOCK);

        if(connect(s,(struct sockaddr*)&saddr, sizeof(saddr)) == -1) {
                if (errno == EINPROGRESS){// it is in the connect process
                        struct timeval tv;
                        fd_set writefds;
                        tv.tv_sec = m_nTimeOut;
                        tv.tv_usec = 0;
                        FD_ZERO(&writefds);
                        FD_SET(s, &writefds);
                        if(select(s+1,NULL,&writefds,NULL,&tv)>0){
                                int len=sizeof(int);
                               //下面的一句一定要，主要针对防火墙
                                getsockopt(s, SOL_SOCKET, SO_ERROR, &error, &len);
                                if(error==0) ret=TRUE;
                                else ret=FALSE;
                        }else   ret=FALSE;//timeout or error happen
                }else ret=FALSE;
        }
        else    ret=TRUE;

        close(s);
        return ret;
}