使用curl报couldn't connect to host异常

//发送post请求function _xpost($url,$p){    $f='';    $data='';    foreach($p as $k=>$v)    {        $data.=$f.$k.'='.urlencode($v);        //$data.=$f.$k.'='.$v;        $f='&';    }    //echo $data.'</br>';    $curl = curl_init($url);    curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, 1);      curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);      curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);    curl_setopt($curl, CURLOPT_POST, 1);    curl_setopt($curl, CURLOPT_POSTFIELDS, $data);    $res = curl_exec($curl);    if(curl_errno($curl))    {        echo 'Curl error: ' . curl_error($curl);    }    curl_close($curl);    return $res;}