Question

I’ve been learning C++ and I am practicing with classes at the moment.
I created a class that stores a name and a score of a player and defines functions to
manipulate the data and show it.

One of the functions I created is to compare scores of two players and return a pointer
to the player with the higher score. This is the function:

Player * Player::highestScore(Player  p2)const
{
    if(p2.pScore>pScore)
    {
        return &p2;
    }
    else
    {
        return this;
    }
}

From the main I create the following players:

Player p1("James Gosling",11);
Player *p4 = new Player("Bjarne Stroustrup",5);

I call the highestScore function:

Player *highestScore = p1.highestScore(*p4);

However as you may have noticed from reading the function itself, when I return the pointer to the object that called the method (if it has a higher score), I get an error that says:

return value type does not match the function type

This problem seems to disappear when I declare the return type of the function as a const, like this:

const Player * Player::highestScore(Player  p2)const

The part that is confusing me is why does it allow me to return &p2, which is not const and doesn’t allow me to return this, which is a pointer to the object that called the function, which isn’t a const as well? Also even when I declare the function return type as a const, it still allows me to return &p2, even though the argument passed to the parameter is not a const Player object?

Sorry if the question seems strange or what I’m trying to do is very bad programming, but it’s just for the purpose of learning by doing it.

Answer 1

The part that is confusing me is why does it allow me to return &p2, which is not const and doesn’t allow me to return this, which is a pointer to the object that called the function, which isn’t a const as well?

this is const (or, more accurately, is a pointer-to-const) in a const member function, just like all the data members:

#include <iostream>
#include <type_traits>

struct A
{
    void foo()
    {
        std::cout << std::is_same<decltype(this), const A*>::value << '\n';
    }

    void bar() const
    {
        std::cout << std::is_same<decltype(this), const A*>::value << '\n';
    }
};

int main()
{
    A a;
    a.foo();
    a.bar();
}

Output:

0
1

---

Also even when I declare the function return type as a const, it still allows me to return &p2, even though the argument passed to the parameter is not a const Player object?

We can’t see what you tried, but presumably it was Player* const, which is not the same as Player const* (or const Player*). You can add constness to &r2 just fine; taking constness away is a different story.