CODEWITHSUNDEEP
c++stlcontainers
Dave
Dave

Reputation: 7623

Dealing With Dynamically Allocated Memory in Container Classes

I am having some difficulty understanding how containers are implemented in C++. Specifically, how can I deal with data allocated on the stack vs data allocated on the heap. For instance:

vector<int> VectorA;
VectorA.push_back (1);
VectorA.push_back (2);
VectorA.push_back (3);

vector<int*> VectorB;
VectorB.push_back (new int (1));
VectorB.push_back (new int (2));
VectorB.push_back (new int (3));

How does one deal with making sure the integers in VectorB are deleted properly. I remember reading somewhere that std::vector only calls the destructor and doesn't actually delete anything. Also, if I wanted to implement my own LinkedList class, how would I deal with this particular problem?

Upvotes: 1

Views: 1055

Answers (3)

Jerry Coffin
Jerry Coffin

Reputation: 490713

The short answer is that most don't deal with such things at all. The standard containers (e.g., std::vector) don't store the original object at all -- they store a copy of the object. They manage the storage for their own copy, and it's up to you to manage the storage for the original.

In the case of storing pointers, you're basically taking responsibility for managing the storage pointed to by the pointer. The container is still making (and managing the storage for) a copy, but it's just a copy of the pointer, not the object to which it refers. That's up to you to deal with.

Upvotes: 0

Bo Persson
Bo Persson

Reputation: 92381

The objects stored in the vector are stored on the heap anyway (in space allocated by the vector).

There is very little advantage in allocating the objects separately (option B), unless you intend to manage them somehow outside of the vector. In that case the vector can just destroy the pointers it stores, and trust the real owner to destroy the objects themselves.

Upvotes: 2

Alok Save
Alok Save

Reputation: 206646

The ideal way to deal with the problem is by using Smart Pointers as elements of your container instead of raw pointers.
Otherwise you have to manually do the memory management yourself.

Upvotes: 4

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