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C++ Brain Teasers: Exercise Your Mind

Discussion: Monsters on the Move

Understand the difference between move and copy constructors by analyzing object initialization with std::move in C++. Learn to identify common issues and fix move constructor implementations to write efficient, correct code.

We'll cover the following...

Run the code

Now, it’s time to execute the code and observe the output.

C++ 17
#include <iostream>
struct Monster
{
    Monster() = default;
    Monster(const Monster &other)
    {
        std::cout << "Monster copied\n";
    }
    Monster(Monster &&other)
    {
        std::cout << "Monster moved\n";
    }
};
struct Jormungandr : public Monster
{
    Jormungandr() = default;
    Jormungandr(const Jormungandr &other) : Monster(other)
    {
        std::cout << "Jormungandr copied\n";
    }
    Jormungandr(Jormungandr &&other) : Monster(other)
    {
        std::cout << "Jormungandr moved\n";
    }
};
int main()
{
    Jormungandr jormungandr1;
    Jormungandr jormungandr2{std::move(jormungandr1)};
}

Understanding the output

When we initialize the second Jormungandr with a moved-from object, the move constructor gets called for Jormungandr but the copy constructor for Monster. Why is that?

As we learned in the ...