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

Subject: Re: [Boost-users] boost::xpressive - Regex stack space exhausted
From: Eric Niebler (eric_at_[hidden])
Date: 2010-07-21 16:52:47

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