c# Regex Valid Dates (without following digits )

Posted on 2014-02-26
Last Modified: 2014-02-26
I am using Regex Magic but I cannot isolate the Valid Dates.
 My regular expression for this is
(?:3[01]|[12][0-9]|0?[1-9])[/.-](?:1[0-2]|0?[1-9])|(?:1[0-2]|0?[1-9])[/.-](?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)|(?:3[01]|[12][0-9]|0?[1-9])[ \t]+(?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)

This was enough for me if I had not the following issue

1.95 with my regex returns 1.9 but this is not valid date for me because has a digit following it. I think there is a way to prevent this but I cannot get there!
Question by:novreisb
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Expert Comment

ID: 39890760
LVL 35

Accepted Solution

Terry Woods earned 500 total points
ID: 39890770
Added a negative lookahead (?!\d) after the numeric month pattern:
(?:3[01]|[12][0-9]|0?[1-9])[/.-](?:1[0-2]|0?[1-9])(?!\d)|(?:1[0-2]|0?[1-9])[/.-](?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)|(?:3[01]|[12][0-9]|0?[1-9])[ \t]+(?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)

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You may want to ensure there's no number preceding it either, with a negative lookbehind:
(?!<\d)(?:3[01]|[12][0-9]|0?[1-9])[/.-](?:1[0-2]|0?[1-9])(?!\d)|(?:1[0-2]|0?[1-9])[/.-](?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)|(?:3[01]|[12][0-9]|0?[1-9])[ \t]+(?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)

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This should cover you for data like:

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where 23.10 would match without the addition to the pattern.

Author Closing Comment

ID: 39890785
Yes, it was not only the following digits but also the precedent ones.  it works perfect!
 Thks Terry
 (ozo, thks, but Terry answer is more complete as you can understand)
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Author Comment

ID: 39890798
Sorry Terry, but the look behind not working! Can you try it?
LVL 35

Expert Comment

by:Terry Woods
ID: 39890818
It's only included for the dates with format:

If you have format:
123 October

Then you'll need a modified pattern. Is that the case you're talking about?

If not, then which case is failing?

Author Comment

ID: 39890827
123.10 is failing! I removed the <  in the (?!<\d)  and it works apparently!
LVL 35

Expert Comment

by:Terry Woods
ID: 39890831
Apologies; I got the < and ! the wrong way around. It's corrected here:
(?<!\d)(?:3[01]|[12][0-9]|0?[1-9])[/.-](?:1[0-2]|0?[1-9])(?!\d)|(?:1[0-2]|0?[1-9])[/.-](?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)|(?:3[01]|[12][0-9]|0?[1-9])[ \t]+(?:Jan|January|Feb|February|Mar|March|Apr|April|May|May|Jun|June|Jul|July|Aug|August|Sep|September|Oct|October|Nov|November|Dec|December)

Open in new window


Author Comment

ID: 39890838
Excellent! Now is Ok! Have a good day that in Portugal is 3.00  AM and go sleep!

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