[Bug libstdc++/48891] std functions conflicts with C functions when building with c++0x support (and using namespace std)

["alexis.menard at openbossa dot org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48891

--- Comment #3 from Alexis Menard <alexis.menard at openbossa dot org> 2011-05-05 22:17:36 UTC ---
(In reply to comment #2)
> (In reply to comment #0)
> > 
> > and build it with : g++ main.cpp -std=c++0x -std=gnu++0x -o test
> 
> There's no point specifying two -std options, only the last one takes effect.
> 
> > If I deactivate the c++0x support it works.
> 
> Because in C++98 there is no std::isnan, so you only get the version in the
> global namespace from <math.h>

That explain.

> 
> > The real issue is that the c++0x standard removes the prohibition on C++
> > headers declaring C names in the global namespace. The problem here is that
> > math.h is included therefore the declarations are in the global namespace.
> 
> I don't think that's the problem, because libstdc++ has always declared the
> names in the global namespace even though it wasn't valid in C++03 - we haven't
> changed that for C++0x (all that happened is the standard was relaxed to
> reflect the reality of actual implementations)
> 

Sorry for my ignorance.

> 
> > I'm not really sure how the compiler can solve that but this new "feature" of
> > c++0x seems to be very annoying. I could solve it by not using namespace std
> > but let say the project is huge, it will requires lot of modifications.
> > 
> > Basically any time you use using namespace std, you may have conflicts with the
> > underlaying C libraries, it's even more annoying with your own namespace
> > because your functions can conflict with all the stuff in the global namespace
> > put by C libraries and it's very common in a cpp file to use "using namespace
> > foo;"
> > 
> > Any suggestions on how I could "workaround" that?
> 
> Qualify isnan explicitly, by calling either ::isnan or std::isnan

Well that requires me to modify my entire project, namely WebKit :(. But the
more I'm stuck on that issue, the more it seems to be the only solution.