Quick C++ question

[XA04]

template <class T>
class Calculator
{
public:
	Calculator(const T &x, const T &y) : _x(x), _y(y) {}
	~Calculator(void){ }
	const T add(void){ return _x + _y; }
	const T sub(void){ return _x -_y; }
	const T mult(void){ return _x * _y; }
	const T div(void){ return _x / _y; }

private:
	const T _x;
	const T _y;
};

The part in bold above. What does the colon mean/do? What's it called?! It's came out of nowhere in my work at uni and in my book. If someone can tell me what it's called then that would be great and I can find out from there.

Cheers!

[XA04]

Nobody?

[oolon]

Nobody?

Constructors.... inhertance? the constructors for your template class is calling the constructors for _x and _y classes with arguments passed to it.... Of course the whole line is inlined because of the {} in the definition.

[XA04]

Constructors.... inhertance? the constructors for your template class is calling the constructors for _x and _y classes with arguments passed to it.... Of course the whole line is inlined because of the {} in the definition.

The thing I don't understand is that there aren't any _x and _y classes? Or is that actually defining those classes right there and then? If so that makes sense!

[oolon]

Here it is at work....

#include <iostream>

class blob
{
public:
  blob(const char *str){std::cout << str;}
};

template <class T>
class Calculator
{
public:
        Calculator(const T &x, const T &y) : _x(x), _y(y) {}
        ~Calculator(void){ }
        const T add(void){ return _x + _y; }
        const T sub(void){ return _x -_y; }
        const T mult(void){ return _x * _y; }
        const T div(void){ return _x / _y; }

private:
        const T _x;
        const T _y;
};


int main()
{
  Calculator<blob> hello("a\n","b\n");
  return 0;
}

[oolon]

The thing I don't understand is that there aren't any _x and _y classes? Or is that actually defining those classes right there and then? If so that makes sense!

They are instances of the class that is passed to the template Calculator... see my example above. The technical term for the classes _X and _Y are arrogated classes of the template class. What that means they are instances of classes are used inside the class rather than extending them to provide new functionality.