From: George Petasis (petasisg_at_[hidden])
Date: 2008-01-11 12:21:03
O/H Eric Niebler ÎγÏαψε:
> George Petasis wrote:
>> Actually, xpressive throws an exception:
>>
>> xpressive error: error_stack: There was insufficient memory to determine
>> whether the regular expression could match the specified character
>> sequence. (12)
>>
>> Any ideas on that? can I increase the stack size under windows?
>
> That's some grammar! I'm amazed you actually got it to compile. :-P As
> you've already figured out, you're blowing your stack. I can see some
> ways to simplify your grammar, but I think your best bet would be to
> switch to a parser generator like Boost.Spirit. Xpressive's exhaustive
> backtracking behavior makes it use stack space more greedily than Spirit.
I have used spirit in the past. I am trying to use xpressive, because:
a) it has backtracking (which is really cool :-) )
b) it is easier to get it compile, at least with VC++ 2005 (I get far
more failures with spirit)
But of course, backtracking comes with a cost :-) Stack exhaustion...
>
> If you want to try sticking with Xpressive, here are some things to try:
>
> - Increasing your program's stack size. You're using MSVC? See the
> /STACK switch for the linker.
I have tested up to 262 MB, but no change :-) My grammar is probably too
complex :-). How exactly xpressive uses the stack? Is it a recursive
descendant parser?
>
> - Avoid using by_ref(a_sregex) where it's not really necessary. For
> instance, you have lots of regexes like this:
>
>> s_scl__com_ =
>> (as_xpr(","));
>>
>> s_scl__pvl_ =
>> (as_xpr("-"));
>>
>> s_scl__sls_ =
>> (as_xpr("/"));
>
> Embedded regexes use more stack space and incur a perf hit that you
> wouldn't get if you had used ordinary strings for this instead.
Its in my plans to fix this, and detect only the cases references are
used...
>
> - Use keep() for the parts of your grammar that do not need exhaustive
> backtracking semantics. keep(<some regex>) matches <some regex> and then
> reclaims the stack space used by <some regex>. But then <some regex> can
> only match in one way, and no alternatives are tried.
I didn't know about keep(). I will read the manuals...
>
> - If you have patterns like (string1 | string2 | string3 ...) where
> stringN are simple string literals, you're better off using a symbol
> parser (assuming you're using xpressive 2.0). See
> <http://tinyurl.com/2rd5d7>.
To say the truth, I tried to use a symbol table, but I didn't manage to
get it to compile. I always got an error when I was using the table in
the grammar rules. How can I check what version of xpressive I am using?
Initially, I downloaded the latest release of the boost library. But the
file regex_actions.hpp was missing, so I downloaded an newer release of
xpressive (2.0.1 I think)...
>
> Best of luck!
>
Thanks :-)
Regards,
George