Question

When I initialize a STL container such as a list< vector<char> > using e.g. my_list.push_back(vector<char>(5000, 'T')) is this copied after construction? Or does the compiler invoke the constructor inside list< vector<char> > itself?

Answer 1

In C++03 push_back is defined as void push_back(const T& x);. That means that you are constructing a vector and a const reference to such temporal is being passed to the list. Then the list internally invokes the copy constructor in order to store a copy of such element.

In C++11 there is an extra definition for void push_back(T&& x); that takes an rvalue reference to your temporal vector, and would result in the move constructor being called internally to initialize the copy held by the list.