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Re: [perl #124256] Regex loop for \K in lookbehind

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Karl Williamson
April 28, 2015 22:15
Re: [perl #124256] Regex loop for \K in lookbehind
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On 4/28/2015 3:26 PM, demerphq wrote:
> On 28 April 2015 at 22:28, Karl Williamson <> wrote:
>> On 04/28/2015 06:40 AM, demerphq wrote:
>>> On 28 April 2015 at 13:14,  <> wrote:
>>>> On Mon, 27 Apr 2015, James E Keenan via RT wrote:
>>>>>> I think this is a similar bug to the one I have just
>>>>>> fixed in PCRE.
>>>>> Can you provide a link to that fix?
>>>>> Thank you very much.
>>>> Not very easily (I'd have to check the SVN manual to figure out how to
>>>> search for stuff - I'm a very simple user) and in any case the fix was
>>>> different for PCRE1 and PCRE2. The bug was in the test programs pcretest
>>>> and pcre2test rather than in the library itself (which only does single
>>>> matches). Here is a comment from pcre2test.c:
>>>>       However, even after matching a non-empty string, there is still one
>>>>       tricky case. If a pattern contains \K within a lookbehind assertion
>>>> at the
>>>>       start, the end of the matched string can be at the offset where the
>>>> match
>>>>       started. In the case of a normal /g iteration without special
>>>> action, this
>>>>       leads to a loop that keeps on returning the same substring.
>>>> The code now checks for this case and advances the /g loop by one
>>>> character, just as it does for matching an empty string.
>>> Sounds like we have the same problem in Perl.
>>> Karl, if you dont see a way to fix this then let me know and I will pick
>>> it up.
>>> Cheers,
>>> yves
>> I haven't ever looked at the \K code; I was hoping someone else would look
>> at this.
> Ok, then I will try to find time to address this.

Note that this is a 5.23 item, so there isn't a real urgency

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