[Interest] Fwd: Building app with clang++ and Qt 5.x/gcc_64 SDK

[Ch'Gans]

---------- Forwarded message ----------
From: Chris Gagneraud <chgans at googlemail.com>
Date: 17 June 2016 at 15:15
Subject: Re: [Interest] Building app with clang++ and Qt 5.x/gcc_64 SDK
To: Thiago Macieira <thiago.macieira at intel.com>
Cc: "interest at qt-project.org" <interest at qt-project.org>


On 17 June 2016 at 02:34, Thiago Macieira <thiago.macieira at intel.com> wrote:
> On quinta-feira, 16 de junho de 2016 20:21:40 PDT Ch'Gans wrote:
>> Hi there,
>>
>> I'm on Ubuntu Linux 16.04, i have installed Qt 5.5, 5,6 and 5.7 using
>> the Qt unified online installer. I would like to know if it is
>> supported to build a Qt app using clang++/64 and Qt 5.x gcc/64
>> official binaries.
>
> It is, if the compiler works.
>
>> Right now, I'm having building errors like:
>> ----------------------------------------------------------------------------
>> -------------- ...
>> /usr/bin/clang++ -m64 -g -O0 -Wall -Wextra -pipe -fexceptions
>> -fvisibility=default -std=c++11 -stdlib=libstdc++ -fPIC [...]
>> ...
>> In file included from
>> /home/krys/Qt5.7.0/5.7/gcc_64/include/QtCore/qbytearray.h:52:
>> /usr/include/c++/v1/string:1938:44: error: 'basic_string<_CharT,
>> _Traits, _Allocator>' is missing exception specification
>> 'noexcept(is_nothrow_copy_constructible<allocator_type>::value)'
>> basic_string<_CharT, _Traits, _Allocator>::basic_string(const
>> allocator_type& __a)
>
> The error is inside a file that is not part of Qt. That's not our problem.
> Please fix your compiler and/or the file in question.
>
> Also note how the file is in /usr/include/c++/v1 (libc++), even if your clang
> command-line says -stdlib=libstdc++. Something is really wrong with your
> compiler (assuming the [...] didn't hide anything important).

Yes that was my problem, the full command line had 2 stdlib specs and
so clang would always pick up libc++.
The proper solution in my case (I'm using QBS), is:
cpp.cxxStandardLibrary: "libstdc++";

>
>> I'm not sure if this is a Ubuntu 16.04 bug, a Qt bug or if simply this
>> kind of build is simply not supported.
>
> It is. I compile Qt with Clang on Linux about once a month.
>
> I only test the current version and the upcoming one (respectively right now,
> 3.8 and 3.9). My recommendation is that if you're going to opt for a non-
> standard compiler that is known to produce slightly worse code than the
> default, you should make sure you're using something no more than a year old.
> I will not help with anything older than Clang 3.8 right now.

Ubuntu 16.04 comes with clang 3.8. But their libc++ seems broken.

Thanks a lot Thiago,
Chris

>
> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel Open Source Technology Center
>
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