Change a object by iterator

Question

I try to change an object using an iterator, but I get this Error:

Error 1 error C2662: 'void Item::setCount(int)' : cannot convert 'this' pointer from 'const Item' to 'Item &'

1 IntelliSense: the object has type qualifiers that are not compatible with the member function

This is my code:

void Customer::addItem(Item other)//add item to the set
{
    set<Item>::iterator it;
    it = _items.find(other);

    if (it != _items.end())
    {
        it->setCount( (this->getCount((*it)) + 1) );
    }

    else
        _items.insert(other);
}

And in this line I have error:

it->setCount( (this->getCount((*it)) + 1) );

see the answer about mutable fields in const methods. – UmNyobe Jan 18 '17 at 10:58 — UmNyobe, Jan 18 '17 at 10:58

Sander De Dycker · Accepted Answer · 2017-01-18T13:05:28.217

4

The iterator for an std::set is const, since modifying the entry can impact the ordering.

To get around this, either :

choose a different container
do a delete+add operation (ie. remove the item from the set, modify it, and then add it into the set again)
use mutable on the fields modified by setCount (if appropriate)
use const_cast to cast away the constness of the item before calling setCount (as a last resort)

For the latter two options, make sure that setCount does not modify anything that changes the ordering of Item objects though.

edited Jan 18 '17 at 13:05

answered Jan 18 '17 at 10:57

Sander De Dycker

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Thanks you for comment. What can i do if I want to update the counter of my item if I can't using set ? – Yair B. Jan 18 '17 at 11:04
@Yair - difficult to say without seeing your `Item` class, but your best bet is probably " choose a different container". In your case I would recommend removing the count from the item (after all, an item might have a name, a colour, a weight - but it typically doesn't have a count), and using `std::map` (or `unordered_map`) to store the counts. – Allison Lock Jan 18 '17 at 11:09
1

@YairB. : I've added some more details to my answer, which will hopefully clarify things a bit better. – Sander De Dycker Jan 18 '17 at 13:06

Change a object by iterator

1 Answers1