Re: Regexp performance guarantees

From: Soronel Haetir (soronel.haetir_at_[hidden])
Date: 2021-07-22 05:56:48

I would have thought that '-' would only get confused as a range
specifier when it follows an opening atom. Here it follows a closing
atom (the '9' in 0-9').

I did not think for example that "a-g-z" could possibly be equivalent
to "a-z", that it should only be able to match a, b, c, d, e,f ,g '-'
and 'z'.

On 7/21/21, Gavin Lambert via Boost <boost_at_[hidden]> wrote:
> On 22/07/2021 3:19 am, Phil Endecott wrote:
>> Here's an example of the sort of thing I have:
>>
>> if (!regexp_match(s, regex("[A-Za-z0-9-_/]{1,8192}"))) throw
>> MalformedInput();
>>
>> The Javascript equivalent seems to be fine. In C++, with
>> libstdc++'s regex implementation, it seems to take about 2
>> seconds to run. Boost.Regex didn't like the '-' after the '9'
>> but when I fixed that the execution time became negligible.
>> Boost.Xpressive seems also to be fast.
>
> In pretty much all regexp languages, if you want to match '-' inside a
> character set then you must specify it as the first character
> (immediately following the '['), otherwise it is confused as a range
> specifier.
>
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-- 
Soronel Haetir
soronel.haetir_at_[hidden]