c++ - shrinking a vector

Question

I've got a problem with my terrain engine (using DirectX).

I'm using a vector to hold the vertices of a detail block. When the block increases in detail, so the vector does.

BUT, when the block decreases its detail, the vector doesn't shrink in size.

So, my question: is there a way to shrink the size of a vector? I did try this:

vertexvector.reserve(16);

Answer 1

If you pop elements from a vector, it does not free memory (because that would invalidate iterators into the container elements). You can copy the vector to a new vector, and then swap that with the original. That will then make it not waste space. The Swap has constant time complexity, because a swap must not invalidate iterators to elements of the vectors swapped: So it has to just exchange the internal buffer pointers.

vector<vertex>(a).swap(a);

It is known as the "Shrink-to-fit" idiom. Incidentally, the next C++ version includes a "shrink_to_fit()" member function for std::vector.