Re: [v3] Handle different versions of Solaris 8 <iso/math_iso.h>, <iso/stdlib_iso.h>

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 26 August 2011 18:13, Jonathan Wakely wrote:
> On 26 August 2011 14:09, Paolo Carlini wrote:
>> On 8/26/11 2:59 PM, Rainer Orth wrote:
>>>
>>> Hi Paolo,
>>>
>>>>> Ok for mainline if bootstraps pass?
>>>>
>>>> Not a comment strictly about this patch, but why we have things like #if
>>>> __cplusplus>= 199711L anywhere? For sure the library is not supposed to
>>>> be
>>>> used together with old C++ front-ends.
>>>
>>> I thought about this myself, but at least the overloads are only present
>>> with __cplusplus>= 199711L.
>>
>> I don't understand: isn't __cplusplus now *always* >= 199711L? Or you want
>> to protect vs the user undefining __cplusplus and then defining it to a
>> different value?!? I don't have the Standard at hand (in theory I'm in
>> vacation ;), maybe Marc can help, but I don't think it's legal, is it?
>
> [cpp.predefined]/3:
>
> "If any of the pre-defined macro names in this subclause, or the
> identifier defined, is the subject of a #define or a #undef
> preprocessing directive, the behavior is undefined."
>

More specifically, __cplusplus is ***NOT*** a feature-test macro like
_POSIX_SOURCE that can be set by users to request different language
standards.

Setting __cplusplus will have no effect on the front-end, but might
confuse the library (or other third-party headers) just as using
-D__GXX_EXPERIMENTAL_CXX0X__ without -std=g++0x will cause big
problems, because the front-end will be using -std=c++98 mode but the
library will think C++0x support is enabled.  Doing this will cause
pain.

If there is ***any*** maintenance overhead involved in "supporting"
users who try to redefine __cplusplus then I think it's a mistake.
I'm certainly not going to think of the effects on those users when I
make changes to the library.