Re: abstract class and some questions
on 02/07/14, Todor Atanasov wrote:
Hi guys, it is me again.
I have entered more deep in C++ and I have reached at a point at which my knowledge is a bit....let say limited:)
This is what I want to do:
To have a CArray (just a array, could be vector, list) with objects, that can be a different classes, but all of them have one method process;
In java this is done with abstract class and then type cast, for example
abstract class Base
{
public abstract void process();
}
class Floor extends Base
{
public void process();
}
and for the loop I can have
List<Floor> objects = new ArrayList<Floor>();
for (int i = 0; i < objects.size(); i++)
{
objects.get(i).process();
}
but how to make that in C++
Here you go:
#include <vector>
#include <iostream>
// Note: No keyword "interface" in C++, interfaces are just
// classes that only contain pure virtual methods.
class Base
{
public:
// Note: The keyword "virtual" is needed in C++. In Java
// all methods are virtual. The "= 0" is the
// C++ way of saying that the method is abstract.
virtual void process() = 0;
};
class Floor : public Base
{
public:
virtual void process() {
std::cout << "I'm a floor, and I am being processed.";
}
};
int main () {
std::vector<Base*> container;
container.push_back(new Floor());
for (int i = 0; i < container.size(); i++)
{
container[i]->process();
}
}
Disclaimer: I intentionally left out anything related to memory
management. Above program will leak memory. A proper production code
interface should have a virtual destructor as well (there are very very
rare cases where this is not necessary), so that the objects can be
cleaned up properly.
I can make the two classes with Base having a pure virtual method process.
But how to make the cast of Base to Floor. To me that is impossible because how would the compile knows how to do it.
You don't need to cast the object to the actual sub-type in order to
access their methods. That's what virtual method have been designed for.
The purpose of all that is that I need to process objects from different classes and I don't know how to do it.
Regards,
Stuart