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Re: chosing a C++ version/compiler

On 28.04.2017 12:06, Jonathan Perkin wrote:
> * On 2017-04-24 at 13:50 BST, Joerg Sonnenberger wrote:
>> On Mon, Apr 24, 2017 at 02:07:17PM +0200, Edgar Fuß wrote:
>>> Is C++n a superset of C++m for n>m?
>> Mostly. There are a couple of things that explicitly create problems for
>> m == 2003 and there is the problem of at least one semantic change that
>> can potentially result in miscompiled code (destructors are tagged as
>> not throwing by default in 2011). For m>=2011 it should be transparent.
> In that case what about something like this:
> tl;dr: introduce CXX_REQD as a similar mechanism to GCC_REQD, packages
> append to it what they need, then we distil it to the most recent
> version and use that for the build.
> todo: set GCC_REQD based on it, i.e. if CXX_REQD>= c++11 then
> automatically set GCC_REQD+=4.7 or whatever
> This is running through a bulk build at present.
>> There is also the ABI breaking mess in libstdc++ to consider of course,
>> i.e. depending on how libstdc++ from GCC 5.1+ is installed, code
>> compiled with -std=c++11 may or may not link correctly with -std=c++03.
> I'm coming to the conclusion that we basically punt on this, and if
> users want to ensure that things work well they need to choose
> up-front a suitable compiler to use for all their builds that will
> satisfy all of their *_REQD.  This is basically what we (Joyent) do
> currently, though at some point we'll need to go to newer than GCC 4.9
> for the latest C++ stuff.

I would promote gnu++* variations always over c++* unconditionally. A
user specifies c++11, c++14, c++17 and Makefiles translate it to
gnu++11, gnu++14, gnu++17 etc. GNU variation is often required for
portable software to Windows.

I'm not convinced about using names like c++0x, they are deprecated in
newer compilers. Older ones don't necessarily support all the needed
features from the standard.

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