Gentoo Archives: gentoo-dev

From: Sven Eden <sven.eden@×××.de>
To: gentoo-dev@l.g.o
Subject: Re: [gentoo-dev] How to support C++11 in libraries?
Date: Fri, 20 Dec 2013 11:56:52
Message-Id: 1479290.p0qqMGJcP8@sed-notebook
In Reply to: Re: [gentoo-dev] How to support C++11 in libraries? by "Jan Kundrát"
1 Am Donnerstag, 19. Dezember 2013, 16:23:08 schrieb Jan Kundrát:
2 > On Thursday, 19 December 2013 16:00:13 CEST, Ian Stakenvicius wrote:
3 > > A change in profiles? 14.0/* adds that to the default CXXFLAGS in
4 > > base, new stage3's etc are all rolled with this. We recommend
5 > > migration to 14.0 profile and have a check somewhere about
6 > > "-std=c++11" missing from CXXFLAGS in case it's overridden in
7 > > make.conf, so users put it in place?
8 >
9 > Before you invest any more time in this, please understand that C++98 and
10 > C++11 are source-incompatible. There is no way to expect that a package
11 > builds fine when you throw -std=c++11 on it. And even if you patched them
12 > all, you are breaking an unknown number of 3rd party software over which
13 > you have exactly zero control.
15 No. If you do something against the standard that is working due to lack of
16 control when compiling with -std=c++98, then your source code is severly
17 broken. Most developers will use C++03 (plus tr1) anyway, won't they?
19 And no, the languages are _not_ "source-incompatible". That would be a
20 scandal!
22 But if you have your C++98/03 code, and do what most developers do and let
23 your console be flooded with warnings you ignore, you must not be surprised,
24 if the compilation fails when you decide to throw
25 "-std=c++11 -Wall -Wextra -Wpedantic -fsanitize=address -fsanitize=thread"
26 with gcc 4.8.2 at it.
28 There is absolutely no reason to expect a compilation to fail with C++11, if
29 it went well with C++03 and "-Wall -Wextra -pedantic".
31 If you try to outsmart your compiler, it will get it's revenge very soon and
32 very hard.
34 And according to [1] it goes even further:
35 Quote:
36 > If you use C++11 then in general you can combine C++11 code built with GCC
37 > 4.X and C++03 code built with any GCC, but there is not the same guarantee
38 > that you can combine with C++11 code built with GCC 4.Y or GCC 4.Z, because
39 > the C++11 features are not all stable yet (e.g. for GCC 4.9 I'm about to add
40 > a new virtual function to a base class in <future>.) This is why C++11
41 > support is still labelled "experimental", because it would be worse to claim
42 > it's stable and then have to break the ABI.
44 So basically C++11 <-> C++03 is no problem at all (unless you *export* certain
45 symbols [2]), but combining C++11 from different gcc versions is nowhere
46 guaranteed to work.
48 Cheers
50 Sven
53 [1] :
54 [2] :


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Subject Author
Re: [gentoo-dev] How to support C++11 in libraries? "Jan Kundrát" <jkt@g.o>
Re: [gentoo-dev] How to support C++11 in libraries? Ian Stakenvicius <axs@g.o>