/**
 * is_external_link 檢測字符串是否包含外鏈
 * @param string $text 文字
 * @param string $host 域名
 * @return boolean    false 有外鏈 true 無外鏈
 * /
function all_external_link($text = '', $host = '') {
  if (empty($host)) $host = $_SERVER['HTTP_HOST'];
  $reg = '/http(?:s?):\/\/((?:[A-za-z0-9-]+\.)+[A-za-z]{2,4})/';
  preg_match_all($reg, $text, $data);
  $math = $data[1];
  foreach ($math as $value) {
    if($value != $host) return false;
  }
  return true;
}