C# 按不同的字节编码，通过字节数去截取字符串

 

        /// <summary>
        /// 按不同的字节编码，通过字节数去截取字符串
        /// 数据库utf-8 1个数字、字母、英文符号算1个长度 1个中文、中文符号算3个长度
        /// </summary>
        /// <param name="origstr">需截取的字符串</param>
        /// <param name="byteslength">需截取的字节长度</param>
        /// <param name="dstencoding">截取的字节编码类型</param>
        /// <returns></returns>
        public static string getsubstring(string origstr, int byteslength, encoding dstencoding)
        {
            if (origstr == null || origstr.length == 0 || byteslength < 0)
                return "";
            int bytescount = dstencoding.getbytecount(origstr);
            if (bytescount > byteslength)
            {
                int readylength = 0;
                int bytelength;
                for (int i = 0; i < origstr.length; i++)
                {
                    bytelength = dstencoding.getbytecount(new char[] { origstr[i] });
                    readylength += bytelength;
                    if (readylength == byteslength)
                    {
                        origstr = origstr.substring(0, i + 1);// + "..."; 加省略号
                        break;
                    }
                    else if (readylength > byteslength)
                    {
                        origstr = origstr.substring(0, i);// + "..."; 加省略号
                        break;
                    }
                }
            }
            return origstr;
        }

 

sting newstr = getsubstring(origstr, byteslength, encoding.utf8);