operator overloading in c++ with an integer and an object

Question

I have an assignment about operator overloads. I did 11/13 of them, but I'm stuck on the last 2 (which are similar). I have a linked list class, and I've been assigned to overload list1+(int i), which I've already done. I also need to overload i+list1, and this is where I'm having difficulties, because I also have a cout<< overload. Examples I've found in stackoverflow caused problems with this cout operator (I'm not sure why.)

SortedDoublyLinkedList SortedDoublyLinkedList::operator+(int i)
{
    SortedDoublyLinkedList newlist(*this);
    newlist.add(i);
    return newlist;

}

This is the piece for list+integer, but I couldn't handle the reverse case, as I described.

`cout<<` is not an operator, and neither is `cout`. `<<` is. — Jashaszun, Aug 04 '14 at 21:29
[Operator Overloading](http://stackoverflow.com/questions/4421706/operator-overloading) — chris, Aug 04 '14 at 21:30
think about whether it makes any sense to call a member operator with a parameter on its left hand side... — vsoftco, Aug 04 '14 at 21:32
The linked duplicate clearly describes non-member operators. — Ben Voigt, Aug 04 '14 at 21:47

score 2 · Answer 1 · answered Aug 04 '14 at 21:34

As a non-member function (it may have to be a friend).

 SortedDoublyLinkedList operator+(int i, const SortedDoublyLinkedList& list) 
   {...}

You'll probably also want to rewrite your existing one as:

 SortedDoublyLinkedList operator+(const SortedDoublyLinkedList& list, int i) 
   { ... }

You'll also probably want to have one call the other, or, better, have both call a SortedDoublyLinkedList::Add() method.

score 1 · Accepted Answer · answered Aug 04 '14 at 21:37

1

to implement i+list1 you must define a friend non member operator like

class SortedDoublyLinkedList {
...

friend SortedDoublyLinkedList operator+(int i, const SortedDoublyLinkedList &_list);
};

SortedDoublyLinkedList operator+(int i, const SortedDoublyLinkedList &_list) {
    SortedDoublyLinkedList newlist(_list);
    newlist.add(i);
    return newlist;
}

answered Aug 04 '14 at 21:37

Massimo Costa

1,864
15
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It does not have to be `friend`, there are many approaches to writing a function without having to access private members. – M.M Aug 04 '14 at 22:11
You're right, this implementation doesn't needs to be friend. – Massimo Costa Aug 05 '14 at 07:05

operator overloading in c++ with an integer and an object

2 Answers2