LibCxxOnOlderSystems - and more software that is pushing for gcc

[Yongwei Wu]

On 25 September 2016 at 22:21, Chris Jones <jonesc at hep.phy.cam.ac.uk> wrote:

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> On 25 Sep 2016, at 2:49 pm, Yongwei Wu <wuyongwei at gmail.com> wrote:
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> On 25 September 2016 at 21:35, Chris Jones <jonesc at hep.phy.cam.ac.uk>
> wrote:
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>> On 25 Sep 2016, at 2:25 pm, Brandon Allbery <allbery.b at gmail.com> wrote:
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>> On Sun, Sep 25, 2016 at 8:29 AM, Ken Cunningham <
>> ken.cunningham.webuse at gmail.com> wrote:
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>>> What is happening exactly on my MacPros running 10.11, I wonder?
>>> Software installed by macports on 10.11 is using clang++ (mostly) and g++
>>> (sometimes). clang++ is linking against libc++, and g++ is presumably
>>>  linking against libstdc++ as that is what it does -- yet there appear to
>>> be no visible issues...and these libraries find each other.
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>> An additional complication is that it's not using the same libstdc++:
>> it's using the GPL3 one with C++11 support, not Apple's GPL2/pre-C++11 one.
>> So potentially the clash here is between the two libstdc++ versions, not
>> libstdc++ and libc++.
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>> Indeed, mixing two different libstdc++ runtimes has the same sort of
>> issues as mixing libstd++ with libc++.
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> I actually do not think this is normally an issue. If the dynamic
> libraries​ manage the lifetime of their own object, i.e. do not do
> something like creating an object in a library but not providing a function
> to destroy it (so that the application needs to delete it), bad things
> should not occur. At least that is the only case I am aware of. (I
> encountered this kind of problems on Windows, which was even worse, as each
> new release of MSVC brought in a different C/C++ runtime, which can also be
> either static or dynamic.)
>
>
> Its exactly the same situation as with libc++ v libstdc++. There are ways
> it can be ok and ways you can run into problems. The only guaranteed way (I
> know of) to not have issues is not to do it.
>

​My point is that a well-designed application/library should not do this.
And if it did it, problems might have occurred long ago (esp. on Windows,
supposing a Windows port exists). If things are going on well so far, we
probably do not need to worry much. At least I do not see what we can do to
help the case at the moment.

-- 
Yongwei Wu
URL: http://wyw.dcweb.cn/
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