file_get_contents获取不到网页内容的解决方法

 <?php
$url = "http://jb51.net/index.html";
$ch = curl_init();
$timeout = 5;
curl_setopt($ch, curlopt_url, $url);
curl_setopt($ch, curlopt_returntransfer, 1);
curl_setopt($ch, curlopt_connecttimeout, $timeout);
//在需要用户检测的网页里需要增加下面两行
//curl_setopt($ch, curlopt_httpauth, curlauth_any);
//curl_setopt($ch, curlopt_userpwd, us_name.":".us_pwd);
$contents = curl_exec($ch);
curl_close($ch);
echo $contents;
?>