C ++子类与它们自己的类型及其父类是否相同？

Question

After a semester without C++ but plenty of Java i now i have a lot of new questions.

Given class baseClass and class childClass : public baseClass definitions and, let's say, the instances baseClass bClass(); childClass cClass(); baseClass bClass(); childClass cClass(); , in a Java equivalent context (though in C++) would cClass instanceof bClass be true ?

And, if so(now on polymorphism), would a function add(baseClass &left, baseClass &right) be able to expect ANY of the baseClass 's children as the left and/or right ?

I supose the last question may be misleading, but it still depends on the first one being true, so if needed i'll expand more on that afterwards.

Thank you!

Answer 1

would cClass instanceof bClass be true?

Yes

would a function add(baseClass &left, baseClass &right) be able to expect ANY of the baseClass's children as the left and/or right?

Yes. This is called upcasting (because you are moving up the hierarchy) and is the concept behind runtime polymorphism in C++. Consider the example below

class A
{
public:
  func()
  {
    cout << "A";
  }
};

class B : public A
{
public:
  func()
  {
    cout << "B";
  }
};

void foo(A &obj)
{
  obj.func();
}

int main()
{
  A a;
  B b;

  foo(a);

  cout << endl;

  foo(b);

  return 0;
}

Output:

A 
B

We can safely supply reference to child class object to a function expecting a reference to base class object because whatever exists in base class will exist in child class.