How can I parse a date with a two-digit year?

[Danny Tuppeny]

I've got a string like this that I need to parse:

01/02/16 12:11:12

The format is dd/MM/yy hh:mm:ss. I'm parsing it like this:

import 'package:intl/intl.dart';

final dateFormat = new DateFormat("d/M/y H:m:s");

main() {

  date = dateFormat.parse("01/02/16 12:11:12");

}

However the year comes out at 0016. I can't find any option to parse a two digit year, I can't manipulate the year property of what comes back (year on DateTime is readonly) and the add method takes a duration which only accepts days, no years! :-(

[Günter Zöchbauer]

It's better to use a custom parser instead of package:intl

There should be a few similar (closed) issues in the intl github repo with similar answers.

[Bigluis Vargas]

Shouldn't you use yy:

import 'package:intl/intl.dart';

final dateFormat = new DateFormat("d/M/yy H:m:s");

[Alan Knight]

"yy" probably ought to parse 2-digit years correctly, as that's what it produces. But it doesn't seem to, so that looks like a bug.

But the larger issue is that DateFormat is providing a mechanism for locale-dependent parsing of dates and times. If you just want to parse a fixed format it will be faster and more reliable to use a custom mechanism.

 

On Thursday, August 25, 2016 at 6:46:03 AM UTC-4, Danny Tuppeny wrote:

I've got a string like this that I need to parse:

01/02/16 12:11:12

The format is dd/MM/yy hh:mm:ss. I'm parsing it like this:

import 'package:intl/intl.dart';

final dateFormat = new DateFormat("d/M/y H:m:s");

main() {

  date = dateFormat.parse("01/02/16 12:11:12");

}

However the year comes out at 0016. I can't find any option to parse a two digit year, I can't manipulate the year property of what comes back (year on DateTime is readonly) and the add method takes a duration which only accepts days, no years! :-(

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[Danny Tuppeny]

On Fri, 26 Aug 2016 at 17:36 'Alan Knight' via Dart Misc <mi...@dartlang.org> wrote:

"yy" probably ought to parse 2-digit years correctly, as that's what it produces. But it doesn't seem to, so that looks like a bug.

Should I raise this somewhere?

 

But the larger issue is that DateFormat is providing a mechanism for locale-dependent parsing of dates and times. If you just want to parse a fixed format it will be faster and more reliable to use a custom mechanism.

What do you mean by a "custom mechanism"? Performance is not an issue for this little script, but I'd be interested to know the recommended way of parsing a date in a known format.

Thanks!

[Alan Knight]

On Fri, Aug 26, 2016 at 12:31 PM Danny Tuppeny <da...@tuppeny.com> wrote:

On Fri, 26 Aug 2016 at 17:36 'Alan Knight' via Dart Misc <mi...@dartlang.org> wrote:

"yy" probably ought to parse 2-digit years correctly, as that's what it produces. But it doesn't seem to, so that looks like a bug.

Should I raise this somewhere?

 

Yes, please file a bug.

 

But the larger issue is that DateFormat is providing a mechanism for locale-dependent parsing of dates and times. If you just want to parse a fixed format it will be faster and more reliable to use a custom mechanism.

What do you mean by a "custom mechanism"? Performance is not an issue for this little script, but I'd be interested to know the recommended way of parsing a date in a known format.

There are probably lots of libraries available, but if you have a strictly fixed format, e.g. coming from a log or a known API, where you don't have to worry about the number of digits or invalid formats then it's pretty easy to just read the numbers out of it. e.g. https://dartpad.dartlang.org/daa484eac791be07f9f9687380c9ed65

 

Thanks!

[Danny Tuppeny]

On Fri, 26 Aug 2016 at 20:59 'Alan Knight' via Dart Misc <mi...@dartlang.org> wrote:

Should I raise this somewhere?

 

Yes, please file a bug.

Done!

https://github.com/dart-lang/intl/issues/123

What do you mean by a "custom mechanism"? Performance is not an issue for this little script, but I'd be interested to know the recommended way of parsing a date in a known format.

There are probably lots of libraries available, but if you have a strictly fixed format, e.g. coming from a log or a known API, where you don't have to worry about the number of digits or invalid formats then it's pretty easy to just read the numbers out of it. e.g. https://dartpad.dartlang.org/daa484eac791be07f9f9687380c9ed65

I originally wrote a regex and then I thought "what am I doing, this is crazy, I only want to parse a date in a well described format"! I figured date would've been one of the included batteries :(

[Alan Knight]

On Fri, Aug 26, 2016 at 1:04 PM Danny Tuppeny <da...@tuppeny.com> wrote:

On Fri, 26 Aug 2016 at 20:59 'Alan Knight' via Dart Misc <mi...@dartlang.org> wrote:

Should I raise this somewhere?

 

Yes, please file a bug.

Done!

https://github.com/dart-lang/intl/issues/123

Thanks.

 

What do you mean by a "custom mechanism"? Performance is not an issue for this little script, but I'd be interested to know the recommended way of parsing a date in a known format.

There are probably lots of libraries available, but if you have a strictly fixed format, e.g. coming from a log or a known API, where you don't have to worry about the number of digits or invalid formats then it's pretty easy to just read the numbers out of it. e.g. https://dartpad.dartlang.org/daa484eac791be07f9f9687380c9ed65

I originally wrote a regex and then I thought "what am I doing, this is crazy, I only want to parse a date in a well described format"! I figured date would've been one of the included batteries :(

If you don't want two problems, it's also pretty easy to write as a few substring operations.

Parsing a date in any particular well-described format, where we don't have to deal with variations in the input is pretty easy. But there are a lot of formats, and describing the format to the system is almost as much work as extracting the information. Parsing more ambiguous formats gets ugly very quickly and introduces a lot of overhead.

After all, parsing a Date in a well-described format is included. It's in Date.parse. It just isn't the format you want.