Question

Notice that the Derived class constructor has ii as its first argument, but the argument passed to Base was made equal to i on purpose.

class Base
{
    protected:
    int i;

    public:
    Base(int i) : i(i) {}
};

class Derived : public Base
{
    private:
    int k;

    public:
    Derived(int ii, int k) : Base(i), k(k) {}  // Why not C2065: 'i' undeclared identifier
};

int main()
{

}

Answer 1

Because i is a member variable inherited from Base, so it is defined. You can freely access member variables in initialiser lists, but what you’re doing is accessing a variable before it’s initialised, which is, I believe, Undefined Behaviour.