curl 请求https内容，返回空

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL,$api); 
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);//禁止直接显示获取的内容 重要
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); //不验证证书下同
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false); //
   
    $json = curl_exec($ch); //获取
    curl_close($ch);