使用curl报couldn'tconnecttohost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.'
';

    $curl = curl_init($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;
}