Question

Ok, I can’t get this code work:
I want to concatenate my custom manipulators.
so they will be called like cout << endl is called.
for example I want this:

   emit << event1 << event2 << event3;

here is my code:

class Emit
{
public:
                // ...
    const void operator<<(const Event& _event) const;
}const emit; // note this global

inline const void Emit::operator<<(const Event& _event) const
{
    Start(_event);
}


class Event 
{
               // ...
         const Event& Event::operator<<(const Event& _event) const;
};

inline const Event& Event::operator<<(const Event& _event) const
{
    return _event;
}

However I cant call this:

 emit << event1 << event2 << event3;

I’m eather receiving compile time error, link time errors and what ever I change in my code I get coresponding error no success.

for example this one:

Error 1 error C2679: binary ‘<<‘ : no operator found which takes a
right-hand operand of type ‘const EventHandling::Event’ (or there is
no acceptable conversion) c:\users\admin\documents\visual studio
2010\projects\cppsystem\eventhandling\test.h 18

thanks alot.

Answer 1

Those operators are called from left to right. As such, the first call (emit << event1) must return a reference to Emit:

class Emit
{
public:
    // ...
    Emit const& operator<<(const Event& _event) const;
}const emit; // note this global

Emit const& Emit::operator<<(const Event& _event) const
{
    Start(_event);
    return *this;
}

And now you don’t need to overload operator<< in your Event class anymore.