Re: [Boost-users] boost::xpressive - Regex stack space exhausted

Subject: Re: [Boost-users] boost::xpressive - Regex stack space exhausted
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2010-07-21 21:12:47

On Wed, Jul 21, 2010 at 5:25 PM, Pavol Supa <pavol.supa_at_[hidden]> wrote:
> Thanks Eric for the info. I already saw the "Beware Nested
> Quantifiers" chapter, but in fact, even if i do not use quantifier
> inside the parentheses, it overflows the stack. Regarding the "keep",
> i tried many combinations of putting the subexpressions into keep(), i
> will try this one if it helps

Please do not top post...

You might think of trying Boost.Spirit.Qi, it is a PEG parser (where
xpressive is a Regex parser).  PEG does not explode like regex does
since it is purely greedy and it runs a great deal faster too.

On Wed, Jul 21, 2010 at 5:25 PM, Pavol Supa <pavol.supa_at_[hidden]> wrote:
> On Wed, Jul 21, 2010 at 10:52 PM, Eric Niebler <eric_at_[hidden]> wrote:
>> On 7/21/2010 2:39 PM, Pavol Supa wrote:
>>> Hi,
>>>
>>> I need to match a hex-written byte array, optionally separated with
>>> spaces. So i tried:
>>>
>>> boost::xpressive::sregex r = * ( * blank >> repeat<2,2> (xdigit));
>>> smatch match;
>>> regex_match (input, match, r);
>>>
>>> when i use input of approx. 150 hex pairs, i get an exception "Regex
>>> stack space exhausted" (i use default stack size by Visual studio
>>> 2008)
>>>
>>> This pattern looks quite simple, so I'd like to know, if there is some
>>> fundamental problem with this expressions.
>>
>> Yes. See
>> http://www.boost.org/doc/libs/1_43_0/doc/html/xpressive/user_s_guide.html#boost_xpressive.user_s_guide.tips_n_tricks.beware_nested_quantifiers
>>
>> Not only will this pattern tear through stack, it'll run very slowly.
>> Try this instead:
>>
>> * ( keep(*blank) >> repeat<2,2> (xdigit))
>>
>>> I know i can enlarge the stack manually, but i expect the input to be
>>> cca 10kB long, depending on user input, so i consider it not being a
>>> good solution.
>>
>> --
>> Eric Niebler
>> BoostPro Computing
>> http://www.boostpro.com
>> _______________________________________________
>> Boost-users mailing list
>> Boost-users_at_[hidden]
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