字符串二次处理，补位+截取

需求：字符串A，处理成字符串B

输出结果要求：将字符串处理成icount长度的字符串，

如果字符串A的长度大于icount则依据字符串B进行截取；

如果字符串的长度小于icount的长度则进行补位。

        /// <summary>
        /// 数字纠正，补全11位:
        /// 如果位数大于11位则进行截取；
        /// 如果长度小于（11-basenum长度）则进行补位；
        /// </summary>
        /// <param name="strnum">原始字符</param>
        /// <param name="basenum">填补字符串</param>
        /// <param name="icount">长度</param>
        /// <returns>补位后的字符串</returns>
        private string NumCorrect(string strnum, string basenum, int icount = 11)
        {
            string newnnum = strnum;
            int strnumlength = strnum.Length;
            if (strnumlength == icount)
            {
                return newnnum;
            }

            int idex = strnum.IndexOf(basenum);

            if (idex >= 0)
            {
                newnnum = strnum.Substring(idex, icount);
            }
            else
            {

                int basenumlength = basenum.Length;
                int iadd = strnumlength + basenumlength;

                if (strnumlength < icount && iadd >= icount)
                {
                    int difference = icount - strnumlength;
                    newnnum = basenum.Substring(0,difference) + strnum;

                }
            }
            return newnnum;
        }