php自动给网址加上链接的方法，自动匹配页面里的网址，包含http、ftp等，自动给网址加上链接。

function text2links($str='') {
  if($str=='' or !preg_match('/(http|www\.|@)/i', $str)) { return $str; }
  $lines = explode("\n", $str); $new_text = '';
  while (list($k,$l) = each($lines)) {
    // replace links:
    $l = preg_replace("/([ \t]|^)www\./i", "\\1http://www.", $l);
    $l = preg_replace("/([ \t]|^)ftp\./i", "\\1ftp://ftp.", $l);
    $l = preg_replace("/(http:\/\/[^ )\r\n!]+)/i",
      "<a href=\"\\1\">\\1</a>", $l);
    $l = preg_replace("/(https:\/\/[^ )\r\n!]+)/i",
      "<a href=\"\\1\">\\1</a>", $l);
    $l = preg_replace("/(ftp:\/\/[^ )\r\n!]+)/i",
      "<a href=\"\\1\">\\1</a>", $l);
    $l = preg_replace(
      "/([-a-z0-9_]+(\.[_a-z0-9-]+)*@([a-z0-9-]+(\.[a-z0-9-]+)+))/i",
      "<a href=\"mailto:\\1\">\\1</a>", $l);
    $new_text .= $l."\n";
  }
  return $new_text;
}
  
//使用范例：
$text = "Welcome www.youkud.com:-)";
print text2links($text);