Re: [boost] [lexical_cast] Fast conversion from boost::iterator_range<std::string::iterator>?

Subject: Re: [boost] [lexical_cast] Fast conversion from boost::iterator_range<std::string::iterator>?
From: Michel Morin (mimomorin_at_[hidden])
Date: 2012-01-26 12:58:16

Olaf van der Spek wrote:
> On Thu, Jan 26, 2012 at 6:14 PM, Michel Morin <mimomorin_at_[hidden]> wrote:
>> IIUC, the main concern to implement optimized code is that
>> how to obtain begin and end pointer to CharT from `iter_rng` safely.
>> With C++11-conforming standard library, it is safe to implement
>>
>>    bool operator<<(::boost::iterator_range<std::string::iterator> const& str)
>>    {
>>        if (!str.empty()) {
>>            start = const_cast<CharT*>(&str.front());
>>            finish = start + str.size();
>>        }
>>        else {
>>            start = 0;
>>            finish = 0;
>>        }
>>        return true;
>>    }
>>
>> because `&*(s.begin() + n) == &*s.begin() + n` (`s` is an object of
>> std::basic_string<…>)
>> is guaranteed.
>>
>> But, in C++03, the above code is not safe; the standard does not guarantee that
>> std::basic_string<…> is stored contiguously (though many standard library
>> implementations store it contiguously).
>
> What about using c_str() instead of begin()? It does provide that
> guarantee in C++03.

We cannot use c_str() because we only have iterators.

P.S.
Antony, I created a trac ticket but could not change the owner to you.
Could you take a look at it?
https://svn.boost.org/trac/boost/ticket/6453

Regards,
Michel