std::numeric_limits::round_style

#include <iostream>
#include <limits>
#include <stdexcept>
#include <string>

std::string style_string(std::float_round_style e)
{
  switch (e) {
    case std::round_indeterminate:       return "indeterminate";
    case std::round_toward_zero:         return "toward zero";
    case std::round_to_nearest:          return "to nearest";
    case std::round_toward_infinity:     return "toward infinity";
    case std::round_toward_neg_infinity: return "toward negative infinity";
  }
  throw std::invalid_argument("invalid style");
}

int main()
{
  constexpr std::float_round_style f = std::numeric_limits<float>::round_style;
  constexpr std::float_round_style d = std::numeric_limits<double>::round_style;

  std::cout << "float : " << style_string(f) << std::endl;
  std::cout << "double : " << style_string(d) << std::endl;
}