c# 判斷字元是否是全形, 擷取字串的位元組數 , 擷取字串指定長度位元組數的字串

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1 Encoding.Default.GetByteCount(checkString);  =2 全形 =1 半形

        /// <summary>        /// 擷取字串的位元組長度        /// </summary>        /// <param name="str"></param>        /// <returns></returns>        public static int GetStringByteLength(this string str)        {             int j = 0;            foreach (char c in str)            {                string checkString = c + "";                j += Encoding.Default.GetByteCount(checkString);            }            return j;     }

        /// <summary>        /// 根據位元組數截取字串        /// </summary>        /// <param name="s">輸入的字串</param>        /// <param name="length">要截取的位元組長度</param>        /// <returns></returns>        public static string bSubstring(this string s, int length)        {            if (length>=s.GetStringByteLength())            {                return s;            }            string outStr="";            int j = 0;            foreach (char c in s)            {                string checkString = c + "";                j += Encoding.Default.GetByteCount(checkString);                outStr += c;                if (j>=length) break;            }           return outStr;        }