overloading cast operator

[cesoxa]

Hello guys,

i need a simple code exemple with a overloaded cast operator.

I need to call something like this:

myClass C;

C = (myClass) 20;

where

class myClass {

int x, y;
// and the rest of code
}

and it will set the object proprieties to x=20, y=20

Thanks a lot !

[Raggers]

If you are doing C = (myClass) 20, you need to overload the int cast operator not your class.
What you need is:

class myClass {

int x, y;
myClass & operator= (int);
}

myClass & myClass ::operator= (int asi)
{
	this->a = asi;
	this->b = asi;
	return *this;
}

This will allow you to do:
C = 20

[Disch]

This is actually done by making a constructor, not overloading a cast operator.

Overloading the assignment operator per Ragger's suggestion could also work but is less effective.

[cesoxa]

I know i could overload the assignment operator and to call C = 20, but i really need an example that overloads the typecast operator... and to call C = (myClass) 20. It's a homework for school.

[Disch]

You have your concepts backwards.

Constructors construct an object from a type.
typecast operators produce a type from a constructed object.

Basically:

constructor: takes an int, gives you a myClass
typecast operator: takes a myClass, gives you an int


In this case, you can't make a typecast operator that does what you describe. You'd have to do that with a constructor.

[cesoxa]

ok... meybe it wasn't the best exemple. I will be more specific this time.

#include <iostream.h>


class A {

public:
int x;
A();
operator B();
};

A::A() {
x=1;
}

A::operator B() { B obj1; obj1.x=x; obj1.y=1;return obj1; };



class B: public A {
public:
int y; // int x inherit from class A
B();
echo();
//operator B();
};

//B::operator B() {B obj1; obj1.x = this->x; obj1.y=1; return B;}

B::B() {
x=1;
y=1;
}
B::echo() {
cout<<"x="<<x<<" si y="<<y<<endl;
}







int main () {


B obj1;
A obj2;
obj1=(B) obj2;
obj1.echo();

return 0;

}

So i need a way to convert an object from class A to an class B object.
I also made the following code:

#include <iostream.h>


class B {
public:
int x, y;
B();
echo();
//operator B();
};

//B::operator B() {B obj1; obj1.x = this->x; obj1.y=1; return B;}

B::B() {
x=1;
y=1;
}
B::echo() {
cout<<"x="<<x<<" si y="<<y<<endl;
}


class A {


public:
int x;
A();
operator B();
};

A::A() {
x=100;
}

A::operator B() { B obj1; obj1.x=x; obj1.y=1;return obj1; };





int main () {


B obiect1;
A obiect2;
obiect1=(B) obiect2;
obiect1.echo();

return 0;
}

This works, to define first the class B and second the class A, but the class B then won't inherit from class A.

Thank you for answers.

[Disch]

1) Again, this is better off as a constructor for B. Not as a cast operator for A.

2) This seems like a questionable/bad design anyway. If B inherits from A you probably shouldn't be able to construct a B from an A. Especially not implicitly like this. That would be extremely error prone.



What are the actual classes you're working with here? I don't need the full bodies of them, just their name and what they're supposed to represent.

Maybe if I can see exactly what it is you're trying to do I can give you an idea for a better design.