C++ arrow operator with pre-increment: With or without parentheses is the same?

Question

Question from the course:

Watch the parentheses around the argument of the ++ operator. Are they really needed? What will happen when you remove them?

Initially there was only one cout expression. I added another one to see the difference, like so:

#include <iostream>
using namespace std;

class Class {
public:

    Class(void) {
        cout << "Object constructed!" << endl;
    }

    ~Class(void) {
        cout << "Object destructed!" << endl;
    }
    int value;
};

int main(void) {
    Class *ptr;

    ptr = new Class;
    ptr -> value = 0;
    cout << ++(ptr -> value) << endl;
    cout << ++(ptr -> value) << endl;
    delete ptr;
    return 0;
}

My idea was to test it again without parentheses and see what is different:

    ...
    cout << ++ptr -> value << endl;
    cout << ++ptr -> value << endl;
    ...

The result is the same in both cases. Thus I conclude: No difference.

Can someone explain and correct please? Why would they ask that question if there is no difference? My feeling is there is a subtlety I am missing.

Result:

Object constructed!
1
2
Object destructed!

Answer 1

There is no difference because -> has a higher precedence than ++. This means that ++ptr -> value is always parsed as ++(ptr->value).

Regardless of how the compiler will see your code, you shouldn't write it like that, because someone who doesn't know C++ operator precedence rules might think the code does something different from what it actually does. ++(ptr->value) is far clearer.