C++ Operator overloading example

Question

Well, I\'m new to operator overloading, and I found this problem. Instead of documenting myself, I prefer to ask you :D

The point is, I know how to do simple operator ov

Answer 1

It's quite easy, don't panic :)

You have recognized the problem well: it's very similar to the std::cout - std::endl work.

You could do like such, though I'll rename the types, if you don't mind.

struct EndMarker {};
extern const EndMarker end; // To be defined in a .cpp

class Data
{
public:
  Data(): m_data(1, "") {}

  // Usual operator
  template <class T>
  Data& operator<<(const T& input)
  {
    std::ostringstream aStream;
    aStream << input;
    m_data.back() += aStream.str();
  };

  // End of object
  Data& operator<<(EndMarker) { m_data.push_back(""); }

private:
  std::vector<std::string> m_data;
}; // class Data

It works by adding to the current last element by default, and pushing an empty element at the end.

Let's see an example:

Data data;
data << 1 << "bla" << 2 << end << 3 << "foo" << end;

// data.m_data now is
// ["1bla2", "3foo", ""]

The other solution would be to keep a flag (boolean) to store if a end has been streamed or not, and if it has, creating a new element on the next insertion (and erasing the flag).

It a bit more work on insertion, but you don't have the empty element... your call.

Answer 2

The trick is to return a reference to youself from operator << - this way, the operator can be 'stacked'.

class me {

    me& operator<<(int t) {...; return *this;}
};

me m;
m << 4 << 5 << 6;

Just overload the shift operator for all types you wish to support (or make it a template if you can afford the danger)!

Answer 3

template <typename T>
dxfdata & operator <<( dxfdata & d, const T & t ) {
   std::ostringstream os;
   os << t;
   d.b += os.str();
   return d;
}