Swap two entire vectors/queue/stack time cost?

Question

For example:

v1 = {1,2,3},    v2 = {4,5};
swap(v1, v2);

now v1 = {4,5}, v2 = {1,2,3}

I think it should be very fast with no regards of the length of these two vectors right? It's just swapping pointers?

Answer 1

1. I think it should be very fast with no regards of the length of these two vectors right?

Yes. std::swap for std::vector 's complexity is guaranteed to be constant time by the stardard:

23.3.6.3$10,11 [vector.capacity](bold by me):

void swap(vector& x);
Effects: Exchanges the contents and capacity() of *this with that of x.
Complexity: Constant time.

And by $23.3.6.6/1 [vector.special], std::swap for std::vector is Specialized as:

template <class T, class Allocator>
void swap(vector<T,Allocator>& x, vector<T,Allocator>& y);
Effects:
x.swap(y);

Here're some more explanations: std::vector::swap and std::swap(std::vector)

Exchanges the contents of the container with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.

Complexity : Constant.

2. It's just swapping pointers?

Basically, it depenes on the implementation of the STL you're using, but it is the most common way to achieve it.