XML 十六进制值 是无效的字符错误 解决方法之一

/// <summary>
/// 过滤非打印字符
/// </summary>
/// <param name="tmp">待过滤</param>
/// <returns>过滤好的</returns>
private string ReplaceLowOrderASCIICharacters(string tmp)
{
StringBuilder info = new StringBuilder();
foreach (char cc in tmp)
{
int ss = (int)cc;
if (((ss >= 0) && (ss <= 8)) || ((ss >= 11) && (ss <= 12)) || ((ss >= 14) && (ss <= 32)))
info.AppendFormat(" ", ss);
else info.Append(cc);
}
return info.ToString();
}