Re: [Boost-users] How efficient is the boost::regex library?

Subject: Re: [Boost-users] How efficient is the boost::regex library?
From: Alec Taylor (alec.taylor6_at_[hidden])
Date: 2011-10-27 18:20:54

Thanks John. I would be interested in seeing comparisons of
boost:regex with other regex libraries.

Yesterday I found a fuzzy logic string regex library. Does the
boost::regex library support this?

On Fri, Oct 28, 2011 at 5:10 AM, John Maddock <boost.regex_at_[hidden]> wrote:
>> I am looking for the most efficient open-source C++ regex library.
>>
>> Reading this article: http://swtch.com/~rsc/regexp/regexp1.html - It
>> seems that GNU awk is the best overall:
>> http://pdos.csail.mit.edu/~rsc/regexp-img/grep1p.png
>
> This is all true, but also completely irrelevant.  DFA's have good worst
> case behaviour, but can be many times slower for common cases.  It's also
> impossible to implement a DFA matcher that offers the full range of Perl
> regular expression features (if you think it can be done, congratulations,
> you've just proved that P==NP).
>
> It's also possible to protect the regex engine against runaway "bad"
> expressions and bail out in those cases (this is what Boost.Regex does, it
> throws an exception if the complexity of obtaining a match grows too fast).
>
>> How does the boost::regex library compare?
>>
>> Would you recommend boost::regex as the most efficient one, or would
>> you suggest another?
>
> There's no such thing as best - it all depends on the data being searched
> and the particular regular expression.  In addition since most
> Perl-compatible libraries use much the same algorithm they're all broadly
> similar albeit with different quirks.
>
> HTH, John.
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