#region 过滤非法字符
public static string encoding(string src)
{
  if (src == null)
   return "";
  StringBuilder result = new StringBuilder();
  if (src != null)
  {
   src = src.Trim();
   for (int pos = 0; pos < src.Length; pos++)
   {
    switch (src[pos])
    {
     case '\"': result.Append("''"); break;
     case '<': result.Append("<"); break;
     case '>': result.Append(">"); break;
     case '\'': result.Append("'"); break;
     case '&': result.Append("&"); break;
     case '%': result.Append("&pc;"); break;
     case '_': result.Append("&ul;"); break;
     case '#': result.Append("&shap;"); break;
     case '?': result.Append("&ques;"); break;
     default: result.Append(src[pos]); break;
    }
   }
  }
  return result.ToString();
}
#endregion