derived class

[zio_mangrovia]

This is just didactic example:

#include <iostream>
using namespace std;

struct A {
   void f() { cout << "Class A" << endl; }
};

struct B: A {
   void f() { cout << "Class B" << endl; }
};

void g(A& arg) {
   arg.f();
}

int main() {
   B x;
   g(x);
}

When g() is invoked, A::f() is called even if the argument is referencing to B object.
At compile time, compiler knows only that the argument of function g() will be a reference to object which is derived from A.
Why compiler doesn't see that the argument x passed to a g() is type B ?

[2kaud]

f() needs to be declared as virtual so that polymorphism works correctly for inherited classes.

#include <iostream>
using namespace std;

struct A {
	virtual void f() {
		cout << "Class A" << endl;
	}
};

struct B : A {
	void f() override {
		cout << "Class B" << endl;
	}
};

void g(A& arg) {
	arg.f();
}

int main() {
	B x;
	g(x);
}

This shows
Class B
as expected.