Exercise to test self C++ comprehension

[cppStudent012]

Hi!

Currently I'm doing exercises in the style "what does this program print?" in order to test if I understood correctly how things work in C++.

I have 2 doubts about the following piece of code (which is a shortened version of the real exercise):

*The following program compiles and runs*

#include<iostream>
using namespace std;

class B {
public:
    B() {cout<< " B() ";}
    virtual void g() const {cout <<" B::g ";}
    virtual const B* j() {cout<<" B::j "; return this;}
    void m() {cout <<" B::m "; g(); j();}
    virtual B& n() {cout <<" B::n "; return *this;}
};

class C : virtual public B{
public:
    C() {cout<< " C() ";}
    virtual void g() const override {cout<<" C::g ";}
    virtual void m() {cout<<" C::m "; g(); j();}
    B& n() override {cout<<" C::n "; return *this; }
};

class D : virtual public B{
public:
    D() {cout<<" D() ";}
    virtual void g() {cout<<" D::g ";}
    void m() {cout<<" D::m "; g(); j();}
};

class E : public C, public D{
public:
    E() {cout<<" E() ";}
    virtual void g() const {cout<<" E::g ";}
    const E* j() {cout<<" E::j "; return this;}
    void m() {cout<<" E::m "; g(); j();}
    D& n() final {cout<<" E::n "; return *this;}
};

class F : public E{
public:
    F() {cout<<" F() ";}
    F(const F& x) : B(x) {cout<<" Fc ";}
    void m() {cout<<" F::m "; j();}
};


int main()
{
    F f;             //prints B() C() D() E() F()
    cout<<endl;
    C* p = new F(f); //prints C() D() E() Fc
    cout<<endl;
    D* q = new F(f); //prints C() D() E() Fc
    cout<<endl;
    C* p4 = new E(); //not interested in what this prints, we need this for the pointer
    cout<<endl;
    (p4->n()).m();   //prints E::n B::m E::g E::j
}

1) When this line get executed C* p = new F(f); I don't get why the B() subobject part of the F object doesn't get created.

I printed B() C() D() E() Fc, but the compiler prints is different.
Meanwhile the default construction of an F object prints also B().

What differs the copy construction and the default construction of an F object in this case?

2) When this line gets executed (p4->n()).m(); I don't understand what happens to the invocation object, in particular what happens to its dynamic type when the method n() returns the value.

In this statement I printed E::n D::m D::g E::j and I can't really tell what I am doing wrong.

Any help will be precious, thank you in advance!

[dutch]

1) You haven't overloaded B's copy ctor, and the default copy ctor doesn't print anything. Try adding this to B.

    B(const B& b) { cout << " B(b) "; }

[cppStudent012]

Thank you for answering @dutch!

In the exercise I can't modify the code, I only have to say what do the statements in the main function print.

I understood now what you meant @dutch.
I totally missed that consctructor delegation to B copy constructor, thank you!