将指定字符串按指定长度进行剪切

        ///  <summary>

       /// 将指定字符串按指定长度进行剪切  

        /// </summary>      

       /// <param name="oldStr">需要截断的字符串</param>    

       /// <param name="maxLength">字符串的最大长度</param>      

      /// <param name="endWith">超过长度的后缀</param>      

      /// <returns>如果超过长度，返回截断后的新字符加上后缀，否则返回原字符串</returns>     

      public static string Stringtruncat(string oldStr,int maxLength, string endWith){        

      if (string.IsNullOrEmpty(oldStr))             

       //throw new  NullReferenceException("原字符串不能为空")           

       return oldStr + endWith;      

            if  ( maxLength<1 )             

             throw new Exception ("返回的字符串长度必须大于[0]");

          if (oldStr.Length >maxLength  )         

             {           string strtmp = oldStr.Substring(0, maxLength);        

                 if (string.IsNullOrEmpty(endWith))                

                     return strtmp;     

                else return strtmp + endWith;           }          

           return oldStr;

      }