取得文件扩展名

   /// <summary>    /// 取得文件扩展名    /// </summary>    /// <param name="filename">文件名</param>    /// <returns>扩展名</returns>    public static string GetFileEXT(string filename)    {        if (string.IsNullOrEmpty(filename))        {            return "";        }        if (filename.IndexOf(@".") == -1)        {            return "";        }        int pos = -1;        if (!(filename.IndexOf(@"\") == -1))        {            pos = filename.LastIndexOf(@"\");        }        string[] s = filename.Substring(pos + 1).Split('.');        return s[1];    }