C#中的字串截取(位元組數)

        ///<summary>
        ///功能:精確的按要求截取指定長度的字串
        ///中文算2個英文算一個
        ///參數:str 待截取字元,len 截取長度 symbol 表示字元(....)
        ///</summary>
        public static string GotTopic(string str, int len, string symbol)
        {
            int count = 0;
            string strTemp = "";
            str = NoHTML(str);
            for (int i = 0; i < str.Length; i++)
            {
                if (Math.Abs(((int)(str.Substring(i, 1).ToCharArray())[0])) > 255)
                {
                    count += 2;
                }
                else
                {
                    count += 1;
                }
                if (count <= len)
                {
                    strTemp += str.Substring(i, 1);
                }
                else
                {
                    return strTemp + symbol;
                }

            }
            return str;
        }
        /// <summary>
        /// 過濾掉HTML標籤
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string NoHTML(string str)
        {
            str = Regex.Replace(str, @"(/<.[^/<]*/>)", " ", RegexOptions.IgnorePatternWhitespace | RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"(/<//[^/<]*/>)", " ", RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);
            return str;
        }