[dart-misc] 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.

Post by Danny Tuppeny
01/02/16 12:11:12
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! :-(

[Bigluis Vargas]

Shouldn't you use *yy*:

import 'package:intl/intl.dart';

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

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

Post by Danny Tuppeny
01/02/16 12:11:12
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! :-(

['Alan Knight' via Dart Misc]

"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.

Post by Danny Tuppeny
import 'package:intl/intl.dart';
final dateFormat = new DateFormat("d/M/yy H:m:s");
main() {
date = dateFormat.parse("01/02/16 12:11:12");
}

Post by Danny Tuppeny
01/02/16 12:11:12
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]

Post by 'Alan Knight' via Dart Misc
"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

Post by 'Alan Knight' via Dart Misc
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' via Dart Misc]

On Fri, 26 Aug 2016 at 17:36 'Alan Knight' via Dart Misc <

Post by 'Alan Knight' via Dart Misc
"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

Post by 'Alan Knight' via Dart Misc
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!
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[Danny Tuppeny]

Post by Danny Tuppeny
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

Post by Danny Tuppeny

Post by Danny Tuppeny
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' via Dart Misc]

On Fri, 26 Aug 2016 at 20:59 'Alan Knight' via Dart Misc <

Post by Danny Tuppeny
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

Post by Danny Tuppeny

Post by Danny Tuppeny
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.
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