// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf
#define msg "C++N4606(229)18.3.2.5 Type float_round_style [round.style]p492.cpp"
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>
#include <cstdlib>

namespace std {
enum float_round_style {
round_indeterminate = -1,
round_toward_zero = 0,
round_to_nearest = 1,
round_toward_infinity = 2,
round_toward_neg_infinity = 3
};
}

int main() {
  std::cout << "round_to_nearest=" << round_to_nearest << std::endl;
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppwa17.sh p492
$ clang++ p492.cpp -std=c++17 -Wall
p492.cpp:20:49: error: reference to 'round_to_nearest' is ambiguous
  std::cout << "std::round_to_nearest=" << std::round_to_nearest << std::endl;
                                           ~~~~~^
/usr/local/Cellar/llvm/6.0.0/include/c++/v1/limits:129:5: note: candidate found by name lookup is 'std::__1::round_to_nearest'
    round_to_nearest          =  1,
    ^
p492.cpp:13:1: note: candidate found by name lookup is 'std::round_to_nearest'
round_to_nearest = 1,
^
1 error generated.

$ g++-7 p492.cpp -std=c++17  -Wall
p492.cpp:10:6: error: multiple definition of 'enum std::float_round_style'
 enum float_round_style {
      ^~~~~~~~~~~~~~~~~
In file included from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/string_view:40:0,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/basic_string.h:48,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/string:52,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/locale_classes.h:40,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/bits/ios_base.h:41,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/ios:42,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/ostream:38,
                 from /usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/iostream:39,
                 from p492.cpp:6:
/usr/local/Cellar/gcc/7.3.0_1/include/c++/7.3.0/limits:167:8: note: previous definition here
   enum float_round_style
        ^~~~~~~~~~~~~~~~~