Date 2030 becoming 1930 after conversion

Question

I have some legacy code which we are seeing some issues. For example, if we have,

var dt2030 = new DateTime(2030, 01, 01);
var dt1 = Convert.ToDateTime(dt2030.ToString("dd/MM/yy"));

The dt1 here denotes 1930. Is there any fixed format for yy? I mean if it is 10 years different from current then take older else take a newer year?

ToString should probably be `ToString("dd/MM/yyyy")`. See formats [here](https://learn.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings). — Cicero, Jun 14 '20 at 08:13
I can't reproduce it, get back 2030. Did you check your OS date and time settings? — Pavel Anikhouski, Jun 14 '20 at 08:15
@user960567 Please refer to the remarks section of [`TwoDigitYearMax`](https://learn.microsoft.com/en-us/dotnet/api/system.globalization.gregoriancalendar.twodigityearmax?view=netcore-3.1#remarks) property. _The initial value of this property is derived from the settings in the regional and language options portion of Control Panel_ So, as I already told you, you should check your regional settings — Pavel Anikhouski, Jun 14 '20 at 08:33
Can you talk us through why you have a date which you then convert to a string and **back to a date**? — mjwills, Jun 14 '20 at 11:09
@mjwills, it's all about the legacy code which recently found that some developer doing this. My current challenge is MRZ which just have 2 digits for year https://en.wikipedia.org/wiki/Machine-readable_passport — Imran Qadir Baksh - Baloch, Jun 14 '20 at 11:21
Fundamentally, if you store a 4 digit number in a 2 digit number then you are bound to have issues. ;) — mjwills, Jun 14 '20 at 13:28
This sample code may not be reproducible depending on the OS and the calendar settings, see https://stackoverflow.com/questions/58508724/parsing-12-25-35-to-a-date-using-invariantculture-2-digit-year — manuc66, Jun 17 '22 at 11:49

score 3 · Accepted Answer · answered Jun 14 '20 at 08:24

3

The default calendar goes from 1930 to 2029, hence if you ask it to parse a date of the year 30 it can't be anything else than 1930, by default.

A possible solution is to use CultureInfo and expand the range, then when parsing the date also passing the CultureInfo as parameter, in:

    CultureInfo ci = new CultureInfo(CultureInfo.CurrentCulture.LCID);
    ci.Calendar.TwoDigitYearMax = 2099;

    var dt2030 = new DateTime(2030, 01, 01);
    var dt1 = Convert.ToDateTime(dt2030.ToString("dd/MM/yy"), ci);

    Console.WriteLine(dt1);

answered Jun 14 '20 at 08:24

Balastrong

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[Remarks](https://learn.microsoft.com/en-us/dotnet/api/system.globalization.gregoriancalendar.twodigityearmax?view=netcore-3.1#remarks) section of `TwoDigitYearMax` tells that initial value is derived from region settings – Pavel Anikhouski Jun 14 '20 at 08:31
Mine case TwoDigitYearMax is 2029. So the rule says when 2029 passed we used old century? – Imran Qadir Baksh - Baloch Jun 14 '20 at 08:32
If your years go from 1930 to 2029, if I ask you which year ends with 30 the answer is 1930 :) – Balastrong Jun 14 '20 at 08:35
You can also value using `CultureInfo.CurrentCulture.DateTimeFormat.Calendar.TwoDigitYearMax = 2049;`, without creating a `CultureInfo` – Pavel Anikhouski Jun 14 '20 at 08:37
@PavelAnikhouski and Balastrong the challenge is MRZ(https://en.wikipedia.org/wiki/Machine-readable_passport) where we have 2 digits now what should I put for TwoDigitYearMax? – Imran Qadir Baksh - Baloch Jun 14 '20 at 09:10

score 3 · Answer 2 · answered Jun 14 '20 at 08:29

3

The issue in your code is yy. You have to use yyyy. You should use the correct format yyyy.

var dt2030 = new DateTime(2030, 01, 01);
var dt1 = Convert.ToDateTime(dt2030.ToString("dd/MM/yyyy"));
Console.WriteLine(dt1);

answered Jun 14 '20 at 08:29

Mei

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Yup this is not the intent. Tryiong to understand this – Imran Qadir Baksh - Baloch Jun 14 '20 at 08:29

Date 2030 becoming 1930 after conversion

2 Answers2