Hi guys, my first post in this forum! I've been seeing this website/forum for a short time, and I decided to register myself and solve my questions (if they are solvable)

Ok, straight to the point.

I have this class :

#ifndef CALENDARIO_H
#define CALENDARIO_H


class Calendario {

public :
Calendario();
Calendario(const int& month, const int& day)
: currentMonth(month), currentDay(day) {};
~Calendario();

// Operator I want to overload
Calendario& operator+(const int&);

// Getters
int getCurrentMonth() const { return currentMonth; }
int getCurrentDay() const { return currentDay; }
// Setters
void setCurrentMonth(int& month) { currentMonth = month; }
void setCurrentDay(int& day) { currentDay = day; }

private :

int currentMonth;
int currentDay;
};

#endif /* CALENDARIO_H */


And the implementation of the function member that is causing me troubles :

Calendario& Calendario::operator+(const int& y) {
if ((y + currentDay) < currentMonth) // With the tests I was doing, at least this if should be executed
currentDay += y;
else if ((y + currentDay) > currentMonth) {
for (int i = 0; i < y; ++i) {
currentDay += 1;
if (currentDay == currentMonth) {
currentDay = 0;
currentMonth += 1;
}
}
}
return *this;
}

and the main :

int main(int argc, char** argv) {

Calendario * cal = new Calendario(10, 5);
//cout << cal->getCurrentDay() << endl; // prints 5
//cout << cal->getCurrentMonth() << endl; // prints 10

Calendario * calsum = cal + 2;
cout << calsum->getCurrentDay(); // prints 0
delete cal;
return 0;
}



For what I understand about overloading operators, that should work, but it doesn't. I'm adding 2 to currentDay of the object cal, and then I'm trying to show it by calling calsum->getCurrentDay(), but it prints 0, and I can't understand why. By overloading the operator+ I'm trying to modify the value of currentDay and currentMonth.

These lines :


Calendario * cal = new Calendario(10, 5); // currentMonth = 10, currentDay = 5
Calendario * calsum = cal + 2; // currentMonth = 10, currentDay = 5 (+2 = 7)


So, I create a Calendario object with the value 10 for currentMonth and 5 for currentDay, then, I'm adding 2 to currentDay (for the code of the overloading operator), later, in the overloading operator :


if ((y + currentDay) < currentMonth) // ( (2 + 5) < 10) = true
currentDay += y; // 5+2 = 7 , now currentDay should be 7


Since y + currentDay (7) are lower than currentMonth (10), the new value of currentDay should be 7. After that, I try to print the new value :

Calendario * calsum = cal + 2;
cout << calsum->getCurrentDay();

but it prints 0, and like I've already said at the beggining... I don't know why...

I think I repeat a lot of things trying to explain my error, but now my head is about to explode .

I hope you can help me, and tell me, if you don't mind, what I'm doing wrong.

I'm reading The C Programming Language by Bjarne Stroustrup, and damn... that's a heavy book for a beginner like me . I'm in the chaper Operator Overloading, and till now, i see that my code should work.

Well... I don't know what else to say... if you need more info, just let me know.

PS : Sorry for my english.

Thanks in advance.

First of all you don't need const int&, just a simple (int x) would be suffice, const T& it for classes not primitive types. Also imho, you shouldn't really be using operating+ overloading here. Just write a function to add days to it, take days etc. Because simply just doing cal + 2 doesn't make much sense. Why do you really need for the class to be a pointer?

Calendario * cal = new Calendario(10, 5);
...
Calendario * calsum = cal + 2;

You're never invoking your overloaded operator - you're doing pointer aritmetic.

Calendario * cal = new Calendario(10, 5); // currentMonth = 10, currentDay = 5
Calendario * calsum = cal + 2; // currentMonth = 10, currentDay = 5 (+2 = 7)


cal is actually of type "Calendario pointer" so when you add 2 to it, you're doing pointer arithmetic. calsum is actually pointing to uninitialised memory, so any attempt to use it will result in a crash, debug exception, strange behaviour, etc.

To add 2 to the object itself and not it's pointer, you need to use the dereference operator, *. But in order to use these operators properly, in the way I think you're trying to use them, you should be creating Calendario objects by value and not using the new operator.


Calendario cal(10,5); // Now cal is an actual object and not just a pointer to one
Calendario calsum = cal + 2;


For this to work, the + operator should be returning an entirely new Calendario object, and not a reference to itself.

Wow... that actually worked... I'm such a.... well, I'm just learning, but I should do it well xD.

So, what I've learned today :

- I shouldn't pass built-in types by const.-reference
- The way I was trying to use the operator + with the pointer to Calendario class, is actually pointer arithmetic, so it never calls the operator+ overloaded in the class.
- And finally, the operator+ should return a Calendario object, and not a reference to itself.

I've learned a lot in 5 asnwers, much more than I do reading the book . It's in english, so it cost me a lot to understand all I read.

Thanks a lot guys, thanks for wasting your time answering this noobie question.

By the way, I'm overloading the operator + instead of using a function, just because I want to learn to do this kind of things. Obviously, eventually, I'll do it with a function, but I need to learn to do all these kinds of things. This is just for learning, It's not a homework or anything like that.

I really appreciate all your answers. Thanks a lot again.

See you .

What? That makes no sense. Why on earth would having a reference to an int help in this situation?