Question

Suppose I have the following three classes:

class Animal {};

class Human : public Animal {};

class Dog : public Animal
{
public:
   void setOwner(Animal* owner) { this->owner = owner; }
private:
   Animal* owner;
};

Why is the following allowed, and what exactly is happening?

Dog d;
Human h;

d.setOwner(&h); // ?

At first, I tried to cast it like this d.setOwner(&(Animal)h), but the compiler gave me a warning, and I hit a run-time error.

Edit: the warning the compiler gave me was “taking address of temporary”. Why is this so?

Answer 1

Here
d.setOwner((Animal)&h)

you try to case pointer type to object type. You cannnot do this.

Correct way of casting to Animal class is

d.setOwner((Animal*)&h)

But you

This

d.setOwner(&h);

works because pointers in C++ are automatically cast to a base class if needed. Explicit conversion to Animal* is not needed.