Question about copy constructor

[fl]

Hi,
I browse through C++ primer. I have a question about the calling of
copy constructor in the example of that book. Below, "item" is an
associate container. In main func, there is a call of add_item. From
debug, I see add_item calls "Sales_item(const Sales_item &i)". My
question is: why add_item calls the copy constructor. To you, it may
be very easy. For a beginner like me, I don't know now. Could you give
me an explanation about that? Thanks in advance.





..........................
class Basket {
....
public:
....
void add_item(const Sales_item &item)
{items.insert(item); }

private:
std::multiset<Sales_item, Comp> items;
};
....
class Sales_item {
friend class Basket;
public:
....
// copy control members to manage the use count and pointers
Sales_item(const Sales_item &i):
p(i.p), use(i.use) { ++*use; }

private:
...
};

 

[Victor Bazarov]

Hi,
I browse through C++ primer. I have a question about the calling of
copy constructor in the example of that book. Below, "item" is an
associate container. In main func, there is a call of add_item. From
debug, I see add_item calls "Sales_item(const Sales_item &i)". My
question is: why add_item calls the copy constructor. To you, it may
be very easy. For a beginner like me, I don't know now. Could you give
me an explanation about that? Thanks in advance.





.........................
class Basket {
...
public:
...
void add_item(const Sales_item &item)
{items.insert(item); }

'std::multiset' makes copies of things that you insert. That's
just how all standard containers work.

private:
std::multiset<Sales_item, Comp> items;
};
...

V