php強制用戶轉向www域名

本文主要介紹了php強制使用者轉向www域名的方法，可實現模擬301重定向的功能，並且針對無法head重定向的情況輸出連結。本文實例講述了php強制使用者轉向www域名的方法。分享給大家供大家參考。

具體分析如下：

有時候網站的www域名和非www域名都能訪問網站，但是這樣不利於搜尋引擎的收錄，會分散網頁的權重，所以希望用戶訪問非www的域名時透過301永久重定向到www域名，例如用戶訪問php.cn會直接轉向www.php.cn，本php代碼考慮了無法透過head重定向的情況，會在頁面上輸出鏈接，讓用戶點擊。

// Install info.:
// Copy and paste these lines into your default index.php or
// the file that get's called if a visitor comes on your 
// website...
// read the host from the server environment
$host = $_SERVER["HTTP_HOST"];
// fix host name - we never now... ;-)
$host = strtolower($host);
$host = trim($host);
// This is important: 
// Webbrowsers like Firefox are doing their request without
// the port number like "www.php.cn" but some other 
// applications send host names like "www.php.cn:80" 
$host = str_replace(':80', '', $host);
$host = trim($host);
// if the host is not starting with www. redirect the 
// user to the same URL but with www :-)
if ($host != 'www.php.cn'){
  // You an also change the "!=" to "==", if you want to force 
  // the user to use the domain name without the www. 
  // send status header, so that search engines or other services
  // detect that this is a permanent redirect and not a temporary
  header('HTTP/1.1 301 Moved Permanently');
  // read the URL the user requested:
  $url = isset($_SERVER["REQUEST_URI"]) ? $_SERVER["REQUEST_URI"] : '';
  // redirect the user to the new destination:
  header('Location: http://www.php.cn' . $url);
  // Convert "special" chars -- cause we never now... ;-)
  $url = htmlspecialchars($url);
  // "fallback" link, if the browser is not supporting header redirects
  print &#39;<a href="http://www.php.cn&#39; . $url.&#39;">Please click here</a>&#39;;
  // stop the script execution here
  exit;
}
// If the domain is www.php.cn then go on with your PHP code 
// of with your website...
// BTW: You need to replace php.cn trough your own domain :-D

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