Question

Suppose I have complex objects, like structs containing a huge amount of members – and I want to store them in a vector.

Now vector::push_back(…) works over call-by-reference (rather than call-by-value), so in the first moment the passed object is not copied. But what about later? Does a vector internally store pointers or direct references? When the vector needs to expand, are the contained elements themselves copied or their addresses?

This finally results in the question, if – for large objects – the objects themselves should be stored in a vector or rather pointers to these objects. Is there a kind of best practice for that?

Answer 1

std::vector::push_back saves copy of the object.

If you need performance by avoiding copy, then you could use vector of pointers.

std::vector<BigObject*> objects; //manage memory yourself

Or you can use some sort of smart pointer, so as to avoid managing memory yourself.
For example, you could use std::unique_ptr if your compiler supports it:

std::vector<std::unique_ptr<BigObject>> objects;

If you use pointers (or smart pointers), then copying is still there, but this time, the copy is done for pointers (or smart pointers) which is much cheaper.

From @Loki’s comment:

Or you can use boost::ptr_vector<> which is designed to hold pointers and will return references when accesses thus makeing it easy to use standard algorithms as they all expect objects.