Re: Using C++11

[Chris Vine <chris cvine freeserve co uk>]

On Tue, 30 Jun 2015 12:06:46 +0200
Murray Cumming <murrayc murrayc com> wrote:

> On Tue, 2015-06-30 at 10:53 +0100, Chris Vine wrote:
> > On Tue, 30 Jun 2015 08:32:43 +0200
> > Murray Cumming <murrayc murrayc com> wrote:
> > > On Mon, 2015-06-29 at 19:44 +0100, Chris Vine wrote:
> > > [snip]
> > > > Fedora 23, which will use gcc-5.1 with the new ABI, will have to
> > > > recompile all its C++ binaries (libraries and programs)[1], for
> > > > all versions of C++ those libraries and programs may happen to
> > > > use.
> > > [snip]
> > >
> > > And would you agree that Ubuntu (for instance) will have to do the
> > > same thing when C++11 (--std=c++11) becomes the default in g++ 6,
> > > when they use g++ 6?
> >
> > No.  Assuming gcc-6 still provides libstdc++ with both ABIs (my
> > guess is that gcc will do so for a considerable number of
> > releases), then it would depend on whether ubuntu chooses to use
> > the new ABI instead of the old one for its C++ binaries.
>
> Isn't Ubuntu likely to make the same choice that Fedora has made, at
> least at some point?
>
> Or is Fedora just doing this (using the C++11 libstdc++ API) because
> they really like C++11 and want to make the C++11 experience as good
> as possible?

I would guess that it is because fedora is a fast moving distribution
and they like to press ahead with what everyone will be doing in a few
years' time.

I doubt it is in order to be especially C++ friendly.  The ABI changes
are pretty much irrelevant to the average C++11/14 user.  How often does
your code's performance depend on O(1) rather than O(N) complexity of
std::list::size() (and if this does affect performance in a particular
case, why are you using lists in the first place)?  And how often does
your code rely on the requirement that non-const operator[]() for a
string may not invalidate iterators into the string (C++03 does permit
that, C++11 does not, and is what rules out copy-on-write)?

For what it is worth, I write all my C++11 code with the old ABI, for
the moment.

Chris