Serialize DateTime to least number of characters for storage

Question

I have a limit of 255 characters in a field of a persistent store. In those 255 characters I would like to store the maximum number of Date and time values which could then be deserialized successfully in an application. Would converting them to an int as mentioned here be my only option?

How much precision do you need to store? (seconds? milliseconds? nanoseconds? time zone?) Does the string need to be printable? — SLaks, Dec 06 '12 at 04:01
@SLaks Forgot to mention.. upto minutes only no timezone info required. Non-printable is fine as well. — Raghu, Dec 06 '12 at 04:02
Do you need to encode only the 21st century so far? That only takes four bits for a year. — John Saunders, Dec 06 '12 at 04:07
@JohnSaunders Yes 21st Century only, don't think this app would endure 87 more years. Not to forget the world may end Dec 21 this year. — Raghu, Dec 06 '12 at 04:38

SLaks · Accepted Answer · 2012-12-06T04:08:36.010

1

First, convert each DateTime into an integer value in as few bytes as possible (probably 5 – 8, depending on what you want to preserve).
If you only need to store minutes, 3 bytes will cover 31 years and 4 bytes will cover 8,166 years.

Pack those bytes into a byte array, then convert that byte array to Base64. This will store one date every 6 characters.

Alternatively, pick a non-Unicode encoding and convert the byte array directly to a string This will store one date every 4 non-printable printable characters.

edited Dec 06 '12 at 04:08

answered Dec 06 '12 at 04:02

SLaks

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@Jeroen: I wrote that before he mentioned non-printability. – SLaks Dec 06 '12 at 04:07
@SLaks I just posted a code sample as per your recommendation !! – Raghu Dec 06 '12 at 06:36

score 1 · Answer 2 · answered Dec 06 '12 at 06:35

Thanks @SLaks, Is this how you suggested I go about it (if I did want printable chars):

        [Test]
        public void DateTimeTest()
        {
            var dateTime = new DateTime(2012, 12, 12, 12, 12, 0);
            int intDateTime = Int32.Parse(dateTime.ToString("yymmddHHMM", CultureInfo.CurrentCulture));
            byte[] bytesDateTime = BitConverter.GetBytes(intDateTime);
            string base64 = Convert.ToBase64String(bytesDateTime);

            Debug.WriteLine(base64);    // Prints fIA/SA==

            byte[] newBytesDateTime = Convert.FromBase64String(base64);
            int newIntDateTime = BitConverter.ToInt32(newBytesDateTime, 0);
            var newDateTime = DateTime.ParseExact(newIntDateTime.ToString(), "yymmddHHMM", CultureInfo.CurrentCulture);

            Assert.AreEqual( dateTime, newDateTime );
        }

Instead of using string parsing, you should store the number of minutes since some fixed base date. — SLaks, Dec 06 '12 at 14:55

Serialize DateTime to least number of characters for storage

2 Answers2