Re: cstring_view

From: Klemens Morgenstern (klemens.morgenstern_at_[hidden])
Date: 2022-05-11 04:23:10

On Tue, 2022-05-10 at 21:15 -0700, Marshall Clow via Boost wrote:
> On May 10, 2022, at 8:35 PM, Klemens Morgenstern via Boost
> <boost_at_[hidden]> wrote:
> >
> > Hi y'all,
> >
> > I've hacked together a cstring_view class and would like to ask if
> > it
> > could be included in  boost.utility or boost.core.
> >
> > https://gist.github.com/klemens-morgenstern/fc02dab8b37fc77ac80efbca30f297cf
> >
> > The main motivation is to have a view that works with C-APIs. I
> > also
> > need the char_traits for dealing with odd char semantics for some
> > system APIs. (e.g. environment keys on windows are char-insensitive
> > but
> > preserving).
>
> I don’t see how this is supposed to maintain the invariant ( null
> temination)  w/o it’s own storage.
>

There's a static "" for default initialization.

  BOOST_CONSTEXPR static const_pointer   null_char_()         {return
null_char_(CharT{});}
  BOOST_CONSTEXPR static const char*     null_char_(char)     {return
"";}
  BOOST_CONSTEXPR static const wchar_t*  null_char_(wchar_t)  {return
L"";}

> Consider:
> Â Â Â  cstring_view sv;Â  // is sv-data() pointing to a null-terminated
> string?  If so, where did it come from?
>
>     cstring_view sv1(“abcdefg”)’
>     sv1.substring(3, 2); // what’s the value of strlen(sv.data)
> here?  How can it be 2?
>

The substr returns a string_view if you pass it a second parameter:

  BOOST_CONSTEXPR basic_cstring_view substr(size_type pos = 0) const;
  BOOST_CONSTEXPR string_view_type substr(size_type pos , size_type n)
const;

I can only move the starting character with substr and maintain the
null-terminator, so if I change the end, I'll get a regular
string_view.

> — Marshall
>
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