Re: C++ and feature guards Warning Question

[Yaakov Selkowitz <yselkowitz@cygwin.com>]

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.

-- 
Yaakov