[Bug c++/51146] The name clog for a global variable triggers a segfault inside std::pow

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51146

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Libc++ uses complex<_Tp>(log(abs(__x)), arg(__x));

Even for C++11, which is based on C99, ::clog is not a reserved name in C++
because C++ specifies that <complex.h> just includes the C++ <complex> header,
so defines std::complex and none of the C99 complex routines exist in C++. This
is not a universally popular feature of C++. But it does mean that a strictly
conforming C++ program can use ::clog for whatever purpose it wants.

However, in practice, our implementation doesn't exist in a vacuum and depends
on an underlying system library (which is usually based on POSIX) and so those
symbols are essentially reserved too, even if the C++ standard doesn't say so.

E.g. if you define a symbol called ::fdopen or ::open you're asking for
trouble, even though those are not in ISO C++.

If you want a pure ISO C++ environment that doesn't rely on additional features
of POSIX and C99, maybe you need to look elsewhere.