To be able to enumerate IPv4 addresses in a given range, it should first be possible to compare IPv4 values. Therefore, we should implement at least operator<, but the following listing contains implementation for all comparison operators: ==, !=, <, >, <=, and >=. Also, in order to increment an IPv4 value, implementations for both the prefix and postfix operator++ are provided. The following code is an extension of the IPv4 class from the previous problem:

ipv4& operator++()
{
   *this = ipv4(1 + to_ulong());
   return *this;
}

ipv4& operator++(int)
{
   ipv4 result(*this);
   ++(*this);
   return *this;
}

friend bool operator==(ipv4 const & a1, ipv4 const & a2) noexcept
{
   return a1.data == a2.data;
}

friend bool operator!=(ipv4 const & a1, ipv4 const & a2) noexcept
{
   return !(a1 == a2);
}

friend bool operator<(ipv4 const & a1, ipv4 const & a2) noexcept
{
   return a1.to_ulong() < a2.to_ulong();
}

friend bool operator>(ipv4 const & a1, ipv4 const & a2) noexcept
{
   return a2 < a1;
}

friend bool operator<=(ipv4 const & a1, ipv4 const & a2) noexcept
{
   return !(a1 > a2);
}

friend bool operator>=(ipv4 const & a1, ipv4 const & a2) noexcept
{
   return !(a1 < a2);
}

With these changes to the ipv4 class from the previous problem, we can write the following program:

int main()
{
   std::cout << "input range: ";
   ipv4 a1, a2;
   std::cin >> a1 >> a2;
   if (a2 > a1)
   {
      for (ipv4 a = a1; a <= a2; a++)
      {
         std::cout << a << std::endl;
      }
   }
   else 
   {
      std::cerr << "invalid range!" << std::endl;
   }
}