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

Subject: Re: [Boost-users] boost::xpressive - Regex stack space exhausted
From: Pavol Supa (pavol.supa_at_[hidden])
Date: 2010-07-22 05:47:19

On Thu, Jul 22, 2010 at 11:40 AM, OvermindDL1 <overminddl1_at_[hidden]> wrote:
> On Thu, Jul 22, 2010 at 3:29 AM, 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))
>>
>> So, i tried it. It throws exceptions at ~230 hexdigit pairs.
>> I played with "keep"s, the only 'better' combination is
>>
>> * keep ( (*blank) >> repeat<2,2> (xdigit))
>>
>> which throws when input has 300 pairs
>
> If you were using Boost.Spirit.Qi, then it should 'just work', that
> rule in Boost.Spirit.Qi for a simple match like the above Regex
> version is would be:
>  boost::spirit::qi::rule<Iterator, boost::spirit::blank_type> r =
> *lexeme[xdigit >> xdigit];
>
> It can also parse and stuff it all into a string, a vector, or
> whatever, as characters or parse it into integers/shorts/whatever,
> basically any parsing need can be easily fulfilled, you really should
> try Boost.Spirit.Qi.

Ok, thanks for advise, i will suggest using Boost.Spirit.Qi to my
colleagues, but it is not my decision.

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