C#中英文混合字符串截取函数

/// <summary>
    /// 截断字符串
    /// </summary>
    /// <param name="maxlength">最大长度</param>
    /// <param name="str">原字符串</param>
    /// <returns></returns>
    public static string cutstr(int maxlength, string str)
    {
      string temp = str;
      if (regex.replace(temp, "[\u4e00-\u9fa5]", "zz", regexoptions.ignorecase).length <= maxlength)
      {
        return temp;
      }
      for (int i = temp.length; i >= 0; i--)
      {
        temp = temp.substring(0, i);
        if (regex.replace(temp, "[\u4e00-\u9fa5]", "zz", regexoptions.ignorecase).length <= maxlength - 3)
        {
          return temp + "...";
        }
      }
      return "...";
    }

private string getbytestring(string center, int maxlen, string endstr)
    {
      string temp = center.substring(0, (center.length < maxlen + 1) ? center.length : maxlen + 1);
      byte[] encodedbytes = system.text.asciiencoding.ascii.getbytes(temp);
      string outputstr = "";
      int count = 0;
      for (int i = 0; i < temp.length; i++)
      {
        if ((int)encodedbytes[i] == 63)
          count += 2;
        else
          count += 1;

        if (count <= maxlen - endstr.length)
          outputstr += temp.substring(i, 1);
        else if (count > maxlen)
          break;
      }
      if (count <= maxlen)
      {
        outputstr = temp;
        endstr = "";
      }
      outputstr += endstr;
      return outputstr;
    }