title: Error when using function preg_replace() in php of wampserver
body: <p>I have a function:</p>
  
  <pre><code>function filter($str) { 
              $str = preg_replace("/(à|á|ạ|ả|ã|â|ầ|ấ|ậ|ẩ|ẫ|ă|ằ|ắ|ặ|ẳ|ẵ)/", 'a', $str); 
              $str = preg_replace("/(è|é|ẹ|ẻ|ẽ|ê|ề|ế|ệ|ể|ễ)/", 'e', $str); 
              $str = preg_replace("/(ì|í|ị|ỉ|ĩ)/", 'i', $str); 
              $str = preg_replace("/(ò|ó|ọ|ỏ|õ|ô|ồ|ố|ộ|ổ|ỗ|ơ|ờ|ớ|ợ|ở|ỡ)/", 'o', $str); 
              $str = preg_replace("/(ù|ú|ụ|ủ|ũ|ư|ừ|ứ|ự|ử|ữ)/", 'u', $str); 
              $str = preg_replace("/(ỳ|ý|ỵ|ỷ|ỹ)/", 'y', $str); 
              $str = preg_replace("/(đ)/", 'd', $str); 
              $str = preg_replace("/(À|Á|Ạ|Ả|Ã|Â|Ầ|Ấ|Ậ|Ẩ|Ẫ|Ă|Ằ|Ắ|Ặ|Ẳ|Ẵ)/", 'A', $str); 
              $str = preg_replace("/(È|É|Ẹ|Ẻ|Ẽ|Ê|Ề|Ế|Ệ|Ể|Ễ)/", 'E', $str); 
              $str = preg_replace("/(Ì|Í|Ị|Ỉ|Ĩ)/", 'I', $str); 
              $str = preg_replace("/(Ò|Ó|Ọ|Ỏ|Õ|Ô|Ồ|Ố|Ộ|Ổ|Ỗ|Ơ|Ờ|Ớ|Ợ|Ở|Ỡ)/", 'O', $str); 
              $str = preg_replace("/(Ù|Ú|Ụ|Ủ|Ũ|Ư|Ừ|Ứ|Ự|Ử|Ữ)/", 'U', $str); 
              $str = preg_replace("/(Ỳ|Ý|Ỵ|Ỷ|Ỹ)/", 'Y', $str); 
              $str = preg_replace("/(Đ)/", 'D', $str); 
              $str = preg_replace("/(–)/", ' ', $str); 
              $str = str_replace(" ", "-", str_replace("&amp;*#39;","",$str)); 
              return $str; 
          }
  $test = "Chào thế giới";
  echo filter($test);
  </code></pre>
  
  <p>I using wampserver, when run code is error:</p>
  
  <pre><code>Warning: preg_replace() [function.preg-replace]: Compilation failed: nothing to repeat at offset 5 in C:\wamp\www\xxx.php on line xx
  </code></pre>
  
  <p>How to config this error, if result exactly <code>is chao-the-gioi</code> </p>