C#截取字符串长度方法

方法一、

        /// <summary>

        /// 截取指定长度的字符串

        /// </summary>

        /// <param name="str">要截取的字符串</param>

        /// <param name="len">要截取的长度</param>

        /// <param name="flag">截取后是否加省略号(true加,false不加)</param>

        /// <returns></returns>

        public static string CutString(string str, int len, bool flag)

        {

            string _outString = "";

            int _len = 0;

            for (int i = 0; i < str.Length; i++)

            {

                if (Char.ConvertToUtf32(str, i) >= Convert.ToInt32("4e00", 16) && Char.ConvertToUtf32(str, i) <= Convert.ToInt32("9fff", 16))

                {

                    _len += 2;

                    if (_len > len)//截取的长度若是最后一个占两个字节，则不截取

                    {

                        break;

                    }

                }

                else

                {

                    _len++;

                }





                try

                {

                    _outString += str.Substring(i, 1);

                }

                catch

                {

                    break;

                }

                if (_len >= len)

                {

                    break;

                }

            }

            if (str != _outString && flag == true)//判断是否添加省略号

            {

                _outString += "...";

            }

            return _outString;

        }

 

方法二、

        /// <summary>

        /// 截取指定长度的字符串

        /// </summary>

        /// <param name="str">要截取的字符串</param>

        /// <param name="len">要截取的长度</param>

        /// <param name="flag">截取后是否加省略号(true加,false不加)</param>

        /// <returns></returns>

        public static string CutString(string str, int len, bool flag)

        {

            System.Text.ASCIIEncoding ascii = new System.Text.ASCIIEncoding();

            byte[] bts = ascii.GetBytes(str);

            int _len = 0;

            string _outString = "";

            for (int i = 0; i < bts.Length; i++)

            {

                if ((int)bts[i] == 63)//两个字符

                {

                    len += 2;

                    if (_len > len)//截取的长度若是最后一个占两个字节，则不截取

                    {

                        break;

                    }

                }

                else

                {

                    len += 1;

                }



                try

                {

                    _outString += str.Substring(i, 1);

                }

                catch

                {

                    break;

                }



                if (_len >= len)

                {

                    break;

                }

            }

            if (str != _outString && flag == true)//判断是否添加省略号

            {

                _outString += "...";

            }

            return _outString;

        }

 

方法三、

        /// <summary>

        /// 截取指定长度的字符串

        /// </summary>

        /// <param name="str">要截取的字符串</param>

        /// <param name="len">要截取的长度</param>

        /// <param name="flag">截取后是否加省略号(true加,false不加)</param>

        /// <returns></returns>

        public static string CutString(string str, int len, bool flag)

        {

            if (str == null || str.Length == 0 || len <= 0)

            {

                return string.Empty;

            }



            int l = str.Length;



            #region 计算长度

            int clen = 0;

            while (clen < len && clen < l)

            {

                //每遇到一个中文，则将目标长度减一。

                if ((int)str[clen] > 128)

                {

                    len--;

                }

                clen++;

            }

            #endregion



            if (clen < l)

            {

                return flag ? str.Substring(0, clen) + "..." : str.Substring(0, clen);

            }

            else

            {

                return str;

            }

        }