按字节长度截取字符串

 /// <summary>
    /// 获取指定字节长度的字符串
    /// </summary>
    /// <param name="text">要截取的字符串</param>
    /// <param name="startIndex">开始位置</param>
    /// <param name="length">结束位置</param>
    /// <returns></returns>
    public static string SubstringByte(string text, int startIndex, int length)
    {
        Encoding _encoding = System.Text.Encoding.GetEncoding("GB2312");
        byte[] bytes = _encoding.GetBytes(text);
        try
        {
            return _encoding.GetString(bytes, startIndex, length);
        }
        catch
        {
            return text;
        }
    }