http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48891
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-05-05 22:03:55 UTC --- (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> > 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) > 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
