3. Match Dates, Lab: Regular Expressions C#

Eminem 0 Точки

3. Match Dates, Lab: Regular Expressions C#

Привет Колеги!

За задачата Match Dates имам три възможни регекса. Първият е мой, вторият е на колега а третия е показан от Софтуни в документа със задачата. Онлайн(в Regex101 и RegXr) и трите регекса работят перфектно, мачват си всичко както трябва. Докато след имплементацията им във C#, работи само първия а вторите два не мачват нищо. Ето ги въпросните регекси:

1. Моя: @"\b(?<day>[0-3][0-9])(?:(-)|(.)|(\/))(?<month>[A-Z][a-z]{2})(\1|\2|\3)(?<year>[0-9]{4})\b";

2. На колегата: @"\b(?<day>[\d]{2})([-\/.])(?<month>[A-Z][a-z]{2})\2(?<year>[0-9]{4})\b";

3. Показан от Softuni: @"\b(?<day>\d{2})([-.\/])(?<month>[A-Z][a-z]{2})\2(?<year>\d{4})\b";

Ето го и input-a:

13/Jul/1928, 10-Nov-1934, , 01/Jan-1951,f 25.Dec.1937 23/09/1973, 1/Feb/2016

При един и същ Input, онлайн работят и трите регекса а във Visual Studio само първия.

Има ли някой, който може да обясни разликата в поведението?

Благодаря предварително!

Тагове:

31/07/2019 15:43:23 Fundamentals Module 31/07/2019 15:44:15

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Axiomatik 2422 Точки

Additional explanation given in the SoftUni Regex Lab-exercises for numbering backreferences with named and un-named groups in C# (page 6):

First off, we’re going to put our RegEx in a variable and get a MatchCollection from the string:

@"\b(?<day>\d{2})([-.\/])(?<month>[A-Z][a-z]{2})\2(?<year>\d{4})\b";

Since RegEx works differently across different languages, before we continue, we’re going to set our backreference from \2 to \1. This is because C# backreferences don’t count named capture groups for backreferences. So, change it before we continue.

-This should work without a problem:

@"\b(?<day>\d{2})([-.\/])(?<month>[A-Z][a-z]{2})\1(?<year>\d{4})\b";

-Regex 2 works because there are only two named groups before the backreference occurs.

-Regex 3 doesn't work if not changed because there are two named groups and one un-named group before the backreference.

26/07/2020 13:03:33

Elena123456 235 Точки

Thanks!

I have already understand: in C# group 1 is the first group without name, group 2 is the second group without name..., but all groups with name are after tha last group without name in order from left to the right.

By the way does https://regex101.com/ has the option to set the regex to work correctly for C#?

20/11/2020 14:27:38

Axiomatik 2422 Точки

Not that I know of unfortunately, I always had to double-check when I used some Regex for my C# code (same thing with https://regexr.com). Basically, you only had to be carefull with how groups were being interpreted by C# (named, unnamed, ...). The practise exams will show you what to watch out for and when you get an RunTime error then just check your Regex (https://www.regular-expressions.info/named.html for some additional reading-help).

Best,

20/11/2020 17:08:09 20/11/2020 17:08:37

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