Should I store entire objects, or pointers to objects in containers?

Question

Designing a new system from scratch. I\'ll be using the STL to store lists and maps of certain long-live objects.

Question: Should I ensure my objects have copy co

Answer 1

This really depends upon your situation.

If your objects are small, and doing a copy of the object is lightweight, then storing the data inside an stl container is straightforward and easier to manage in my opinion because you don't have to worry about lifetime management.

If you objects are large, and having a default constructor doesn't make sense, or copies of objects are expensive, then storing with pointers is probably the way to go.

If you decide to use pointers to objects, take a look at the Boost Pointer Container Library. This boost library wraps all the STL containers for use with dynamically allocated objects.

Each pointer container (for example ptr_vector) takes ownership of an object when it is added to the container, and manages the lifetime of those objects for you. You also access all the elements in a ptr_ container by reference. This lets you do things like

class BigExpensive { ... }

// create a pointer vector
ptr_vector bigVector;
bigVector.push_back( new BigExpensive( "Lexus", 57700 ) );
bigVector.push_back( new BigExpensive( "House", 15000000 );

// get a reference to the first element
MyClass& expensiveItem = bigList[0];
expensiveItem.sell();

These classes wrap the STL containers and work with all of the STL algorithms, which is really handy.

There are also facilities for transferring ownership of a pointer in the container to the caller (via the release function in most of the containers).