删除列表中创建的对象

Question

I'm creating some Objects inside a loop and add it to a listwith:

list<MyObject> myList;    
MyObject* ob = new MyObject();
ob.setAttribute("whatever");
myList.push_back(*ob);

After the loop finishes, I'm using the list several times. I've started now a Leak Detector and saw, that I've to delete all the MyObject objects.

How I delete them properly (In the destructor?). Should I use a iterator? But how I get the real object - and not the iterator pointer?

Thanks a lot.

Answer 1

There's absolutely no reason for dynamic allocation here, since the list stores objects by value. All you're doing is copying and discarding a dynamic object; it's leaked immediately since you don't keep a pointer to it anywhere. Just push objects directly, copying a temporary or automatic variable if necessary:

list<MyObject> myList;    
MyObject ob;
ob.setAttribute("whatever");
myList.push_back(ob);

If you did need to store pointers, perhaps for polymorphism, then you'd use smart pointers to avoid leaks:

list<std::unique_ptr<MyBase>> myList;
std::unique_ptr<MyObject> ob(new MyObject);
ob->setAttribute("whatever");
myList.push_back(ob);

If you really want to juggle raw pointers for some reason, then yes, you will have to delete them yourself. You really shouldn't try to do that.

Answer 2

You don't need to delete them, they're copied when added into the list by push_back() . But, you need to delete ob after you used it. Such as:

list<MyObject> myList;    
MyObject* ob = new MyObject();
ob.setAttribute("whatever");
myList.push_back(*ob);
delete ob;

Basically, you don't need to use pointer here, you can just declare ob in stack to avoiding the manual memory management:

list<MyObject> myList;    
MyObject ob;
ob.setAttribute("whatever");
myList.push_back(ob);

And, according to your program's requirment, you can use some kind of smart point to avoiding such manual memory management, such as:

list<std::shared_ptr<MyObject>> myList;    
myList.push_back(new MyObject);
...
// don't need to delete them manually