#include <string>
#include <iostream>
#include <bitset>
#include <cstdint>

std::string toBinaryString(double value)
{
   union
   {
      double d;
      uint64_t i;
   } u;
   u.d = value;
   std::bitset<64> b(u.i);
   return b.to_string();
}

int main(int argc, char* argv[])
{
   double value = 123.456;
   std::cout << toBinaryString(value) << std::endl;
    return 0;
}