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Tip of the Day
Language: C++
Expertise: Intermediate
Jan 31, 2005

Use Functor for Callbacks in C++

Using the callback function in C is pretty straightforward, but in C++ it becomes little tricky.

If you want to use a member function as a callback function, then the member function needs to be associated with an object of the class before it can be called. In this case, you can use functor.

Suppose you need to use the member function get() of the class base as a callback function


class base

{
public:
	int get ()
	{ return 7;}
};
Then, you need to define a functor:

class CallbackFunctor
{
	functor(const base& b):m_base(b)
	{}
	int operator() ()
	{
		return m_base.get();
	}
};
Now you can use an object of CallbackFunctor as a callback function as follows.

Define the function that needs a callback to take an argument of type CallbackFunctor:


void call (CallbackFunctor& f)
{
	cout << f() << endl;
}


int main ()
{
	base b;
	functor f(b);
	call(f);
}
Saurabh Ramya
 
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