Re: [gentoo-dev] RFC: News item regarding c++98 vs c++11

[Anthony G. Basile]

On 10/19/14 19:08, Alex Xu wrote:
> On 19/10/14 06:53 PM, Anthony G. Basile wrote:
>> the default is still gnu++98
> what does this mean, how does it differ from c++98?

Its a gnu dialect.  I'm not sure of the details of how it deviates from 
the strict standard.  I'm more familiar with how c++11 differs from 
c++98.  Google around and let me know what you find.

>
>> in the older ABI, can lead to a crippled system.
> what do you mean, will other packages break too? maybe "may lead to
> non-functioning or possibly broken packages". adjust as necessary; I am
> not familiar with what may break if incompatible libraries are linked
> together.

If you build a library in the "other" abi, then executables which link 
against it may fail.  I say "may" because you might get lucky and just 
miss one of the changes.  See 
https://gcc.gnu.org/wiki/Cxx11AbiCompatibility.  That's only for gcc-4.7 
though.  I got a feeling that list is not complete.

>
>> However, as c++11 gains in popularity and the number of packages using it
>> increase, it is important that users understand these precautions.
> what precautions? what am I supposed to do? is there a option to warn me
> if I try to do something stupid? should I check some packages on my system?

Do nothing.  A careful reading implies that you should not just add 
-std=c++11 or gnu++11 to your compiler flags without knowing that things 
can break.  I can emphasis that at this point.

>
> remember that gcc-4.7 is literally all (standard) gentoo users, so a
> news item needs to be clear about who exactly needs to care about the
> issue, which here appears to be a small subset of "all (standard) gentoo
> users"; namely, those who specifically opt in to using C++11 (or are
> compiling such packages manually).

User fool around with stuff all the time which I like.  This is a 
cautionary note which increases awareness especially when we get bug 
reports.  The real question to my colleagues is whether they think this 
is news worthy or not.  I don't want to turn it into a c++11 gentoo howto.

>
> also, strictly speaking, last I checked, the name of the standard is
> C++11; c++11 is just what gcc takes.
>
> and maybe some links about what could break if I link incompatible
> libraries together would be helpful, since the links don't seem to go
> over that (at least apparently; I did not read the entire contents).
>

Basically what happens is you get unresolved symbols. You will know them 
because of the charactarist c++ mangled names which you can demangle 
with c++filt.

-- 
Anthony G. Basile, Ph.D.
Gentoo Linux Developer [Hardened]
E-Mail    : blueness@g.o
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