timid wrote:
Quote:
#include <iostream>
>
class Fruit
{
public:
virtual const char* get_name() {return "(nothing)";}
|
Use std::string rather than char*.
Also, a function such as "get_name" should usually be declared const.
Quote:
};
>
class Apple: public Fruit
{
public:
const char* get_name() {return "Apple";}
};
>
class Orange: public Fruit
{
const char* get_name() {return "Orange";}
};
>
int main()
{
std::cout << "Test inheritation" << std::endl;
>
Fruit *myfruit1 = new Apple();
Fruit *myfruit2 = new Orange();
Fruit *myfruit3 = new Apple();
>
[...]
>
// The following does not work
std::cout << "Now change myfruit3 from Apple to Orange..." <<
std::endl;
*myfruit3 = *myfruit2;
|
* derefences the pointer, yielding the object it's pointing to.
Consequently, in your example you don't assign the _pointers_, you
assign the _objects_ they are pointing to. That's a huge difference.
Assigning an Orange to an Apple obviously does not do anything because
you did not specify anything to happen in case of such an assignment.
The invisible assignment operator automatically generated by the
compiler is empty. In other words, the Apple is completely unaffected by
the operation.
If you want to assign a pointer to another pointer, you have to write:
myfruit3 = myfruit2;
However, in your program this would have disastrous results because you
would lose the old value of myfruit3, which means you cannot delete your
second Apple anymore. (You'd have to save the old value somewhere, for
example in a temporary pointer variable.)
What do you try to achieve by having myfruit3 point to a different object?
--
Christian Hackl
