C++ and feature guards Warning Question

[Joel Sherrill]

On 4/6/2017 12:25 AM, Yaakov Selkowitz wrote:
> On 2017-04-05 16:18, Joel Sherrill wrote:
>> Trying to compile an open source package for RTEMS, I
>> came across something I need help to figure out how
>> best to address. The package is in C++ and giving a
>> lot of warnings on methods which I would have thought
>> are prototyped. But clearly the compiler settings
>> are tripping the guards different than the package
>> authors expect.
>>
>> Native GCC on CentOS 7 with glibc gives no warnings.
>
> G++ defines _GNU_SOURCE on glibc targets, meaning that -std=c++NN is,
> contrary to the documentation, *not* strict ISO C++:
>
> https://github.com/gcc-mirror/gcc/blob/master/gcc/config/gnu-user.h#L105
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51749
>
> Per my comments in that BZ, I believe there is a better way of doing
> this, but it will require patches to both gcc and glibc.  Once this is
> done -- and while it's on my wishlist, I don't know when I'll have time
> to work on it -- software will finally stop taking -std=c++NN for
> granted.  In the meantime, building for newlib/Cygwin/RTEMS is going to
> be different from glibc in some cases.
>
> In any case, the fix is either to use proper feature test macros, or use
> -std=gnu++NN instead.  I have had to do this on a number of occasions
> while building software for Cygwin.
>

This was for poppler and this minor change to their configure.ac
improved the build warnings immensely.

These issues are always subtle. Thanks for providing the insight.
I did suspect that newlib might be ahead of the curve on precisely
following the standards.

--joel