fenv.hpp broken on clang+glibc

[Marc Glisse <marc.glisse@…>]

Hello,

with clang and glibc, boost doesn't protect against multiple inclusion of bits/fenv.h:

#include <fenv.h> #include <boost/lexical_cast.hpp>

/localhome/glisse2/include/boost/detail/fenv.hpp:22:11: warning: '_FENV_H' macro redefined /usr/include/fenv.h:24:9: note: previous definition is here /usr/include/x86_64-linux-gnu/bits/fenv.h:30:5: error: redefinition of enumerator 'FE_INVALID' ...

Someone apparently thought it was a good idea to add some subtleties to fenv.hpp to help people who misconfigured clang, but that is imho a bad idea and the special case should be removed (note that clang-3.0 has a good default configuration). If you insist on keeping it, please ensure that _FENV_H is not defined.

[Antony Polukhin]

boost/detail/fenv.hpp is not directly included from lexical_cast.hpp Looks like it is a Boost.Math library error:

antoshkka@new:~/boost_maintain/trunk/boost$ grep -r "boost/detail/fenv.hpp" ./
./numeric/interval/detail/c99sub_rounding_control.hpp:#include <boost/detail/fenv.hpp>      // ISO C 99 rounding mode control
./test/execution_monitor.hpp:  #include <boost/detail/fenv.hpp>
./math/tools/config.hpp:   #include <boost/detail/fenv.hpp>

[John Maddock]

(In [76323]) Fix Clang workaround. Fixes #6156.