C#截取字符串

    public class SubStrHelper
    {
        /// <summary>
        /// 截取字符串长度，中文二字节
        /// </summary>
        /// <param name="str"></param>
        /// <param name="length">字节长度</param>
        /// <returns></returns>
        public static string GetSubString(string str, int byteLength, string moreTag = "...")
        {
            string temp = str;
            int j = 0;
            int k = 0;
            for (int i = 0; i < temp.Length; i++)
            {
                // if (Regex.IsMatch(temp.Substring(i, 1), @"[\u4e00-\u9fa5]+"))            //匹配中文
                if (Regex.IsMatch(temp.Substring(i, 1), @"[^\x00-\xff]+"))                  //匹配双字节字符（包括中文）
                {
                    j += 2;
                }
                else
                {
                    j += 1;
                }
                if (j <= byteLength)
                {
                    k += 1;
                }
                if (j > byteLength)
                {
                    return string.Format("{0}{1}", temp.Substring(0, k), moreTag);
                }
            }
            return temp;
        }
    }