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

On Thu, Jul 22, 2010 at 2:33 PM, Eric Niebler wrote:

On 7/22/2010 5:29 AM, Pavol Supa wrote:

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On Wed, Jul 21, 2010 at 10:52 PM, Eric Niebler wrote:

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On 7/21/2010 2:39 PM, Pavol Supa wrote:

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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));

Wait a minute. What does the data you're trying to match look like? Do you know that xdigit only matches a single hex character? Your data should look something like:

00 11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff 00 11 ....

Is that right?

i used data just without spaces, 000000000000...00000 the data are most often without spaces, so i decided meanwhile to use the workaround (it doesn't throw): expr = * repeat<2,2> (xdigit) but if i move the inner expression to a function, it starts throwing (at similar length), i.e.: sregex byte() { return repeat<2,2> (xdigit) } sregex expr = * byte();

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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#bo...

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.

That doesn't sound right. This could be a bug. I'll look at this today.

i tried to debug the parsing, but it looked ok - when there is a non-trivial expression inside (as mentioned above), it goes into recursion, about 12 functions on callstack, and it eats whole (default) stack at those mentioned quantities

-- Eric Niebler BoostPro Computing http://www.boostpro.com _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users