Constructor calling order in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the base class constructor from the derived class.

C++

class Base {
public:
    Base() { std::cout << "Base constructor\n"; }
};

class Derived : public Base {
public:
    Derived() : [1]() { std::cout << "Derived constructor\n"; }
};

int main() {
    Derived d;
    return 0;
}

Drag options to blanks, or click blank then click option'

ADerived

BBase

Cthis

Dsuper

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Derived()' instead of 'Base()' in the initializer list.

Trying to call 'super()' which is not valid in C++.

The derived class constructor calls the base class constructor by naming the base class Base() in the initializer list.

2fill in blank

medium

Complete the code to call the parameterized base class constructor from the derived class.

C++

class Base {
public:
    Base(int x) { std::cout << "Base constructor with " << x << "\n"; }
};

class Derived : public Base {
public:
    Derived(int y) : [1](y) { std::cout << "Derived constructor with " << y << "\n"; }
};

int main() {
    Derived d(5);
    return 0;
}

Drag options to blanks, or click blank then click option'

ABase

Bthis

CDerived

Dsuper

Attempts:

3 left

💡 Hint

Common Mistakes

Calling 'Derived(y)' instead of 'Base(y)' in the initializer list.

Trying to call 'super(y)' which is invalid in C++.

The derived class constructor calls the base class constructor with an argument by naming the base class Base(y) in the initializer list.

3fill in blank

hard

Fix the error in the constructor calling order by completing the code.

C++

class A {
public:
    A() { std::cout << "A constructor\n"; }
};

class B : public A {
public:
    B() { std::cout << "B constructor\n"; }
};

class C : public B {
public:
    C() : [1]() { std::cout << "C constructor\n"; }
};

int main() {
    C c;
    return 0;
}

Drag options to blanks, or click blank then click option'

AB

BA

CC

Dsuper

Attempts:

3 left

💡 Hint

Common Mistakes

Calling A() directly from C's constructor, which is not the immediate base class.

Trying to call 'super()' which is not valid in C++.

Class C inherits from B, so its constructor should call B's constructor explicitly if needed. The base class A's constructor is called automatically by B's constructor.

4fill in blank

hard

Fill both blanks to create a constructor in Derived that calls the Base constructor with an argument and initializes member x.

C++

class Base {
public:
    Base(int a) { std::cout << "Base constructor with " << a << "\n"; }
};

class Derived : public Base {
    int x;
public:
    Derived(int a, int b) : [1](a), [2](b) { std::cout << "Derived constructor with " << b << "\n"; }
};

int main() {
    Derived d(10, 20);
    return 0;
}

Drag options to blanks, or click blank then click option'

ABase

Bx

Cy

DDerived

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Derived' instead of 'Base' to call the base constructor.

Initializing a non-existent member 'y' instead of 'x'.

The constructor initializer list first calls the base class constructor Base(a), then initializes the member variable x(b).

5fill in blank

hard

Fill the blanks to complete the constructor calling order in multiple inheritance.

C++

class A {
public:
    A() { std::cout << "A constructor\n"; }
};

class B {
public:
    B() { std::cout << "B constructor\n"; }
};

class C : public A, public B {
public:
    C() : [1](), [2]() { std::cout << "C constructor\n"; }
};

int main() {
    C c;
    return 0;
}

Drag options to blanks, or click blank then click option'

AA

BB

CA::A

DB::B

Attempts:

3 left

💡 Hint

Common Mistakes

Using scoped names like A::A() instead of just A().

Reversing the order of base constructors.

The constructor of C calls the constructors of both base classes A and B, in the order the bases appear in the inheritance list (A before B).