Re: Regexp performance guarantees

From: Gavin Lambert (boost_at_[hidden])
Date: 2021-07-21 22:57:00

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.