std::numeric_limits::is_iec559

// C++03
static const bool is_iec559;

// C++11
static constexpr bool is_iec559;

#include <iostream>
#include <limits>

int main()
{
  constexpr bool f = std::numeric_limits<float>::is_iec559;
  constexpr bool d = std::numeric_limits<double>::is_iec559;

  std::cout << std::boolalpha;
  std::cout << "float : " << f << std::endl;
  std::cout << "double : " << d << std::endl;
}