php 符转换为 HTML 实体

function d_htmlspecialchars($string) {
 if(is_array($string)) {
  foreach($string as $key => $val) {
   $string[$key] = d_htmlspecialchars($val);
  }
 } else {
  $string = str_replace('&', '&', $string);
  $string = str_replace('"', '"', $string);
  $string = str_replace(''', ''', $string);
  $string = str_replace('<', '<', $string);
  $string = str_replace('>', '>', $string);
  $string = preg_replace('/&(#d;)/', '&1', $string);
 }
 return $string;
}