Re: operator overload

[dark777 via Digitalmars-d-learn]

On Tuesday, 12 December 2017 at 17:13:55 UTC, Biotronic wrote:
On Tuesday, 12 December 2017 at 16:54:17 UTC, Biotronic wrote:
There is no way in C++ to set the format the way you want it. 
If you want binary output, you need to call a function like 
your binario function.

Of course this is not entirely true - there is a way, but it's 
ugly and probably not what you want:

    struct BinStream
    {
        std::ostream& os;
        BinStream(std::ostream& os) : os(os) {}

        template<class T>
        BinStream& operator<<(T&& value)
        {
            os << value;
            return *this;
        }

        BinStream& operator<<(int value)
        {
            os << binario(value);
            return *this;
        }

        std::ostream& operator<<(std::ios_base& (__cdecl 
*_Pfn)(std::ios_base&))
        {
            return os << _Pfn;
        }
    };

    struct Bin
    {
        friend BinStream operator<<(std::ostream& os, const 
Bin& f);
    } bin;

    BinStream operator<<(std::ostream& os, const Bin& f)
    {
        return BinStream(os);
    }

int main()
{
    std::cout << "\n\t127 em binario:     " << binario(127)
        << "\n\t127 em binario:     " << bin << 127
        << "\n\t127 em octal:       " << std::oct << 127
        << "\n\t127 em binario:     " << bin << 127
        << "\n\t127 em hexadecimal: " << std::hex << 127
        << "\n\t127 em binario:     " << bin << 127
        << "\n\t127 em decimal:     " << std::dec << 127
        << "\n\t127 em binario:     " << bin << 127 << "\n\n";
}

What is this black magic? Instead of overriding how 
std::ostream does formatting, Bin::Operator<< now returns a 
wrapper around a std::ostream, which special cases ints. If it 
gets any other format specifiers, it returns the ostream again, 
and the binary formatting is gone.

All in all, I think the conclusion is: Stay with D.

--
  Biotronic

I tried to execute with this part of the code

  std::ostream& operator<<(std::ios_base& (__cdecl 
*_Pfn)(std::ios_base&))
  {
   return os <<_Pfn;
  }

and it returns me this error below what is the include?

bin2.cxx:44:43: error: expected ‘,’ or ‘...’ before ‘(’ token
   std::ostream& operator<<(std::ios_base& (__cdecl 
*_Pfn)(std::ios_base&))
                                           ^
bin2.cxx: In member function ‘std::ostream& 
BinStream::operator<<(std::ios_base&)’:
bin2.cxx:46:16: error: ‘_Pfn’ was not declared in this scope
    return os <<_Pfn;