Question

Possible Duplicate:
std::vector resize downward

If I resize() an std::vector to some size smaller than its current size, is it possible that the vector will ever allocate new memory?

This is important to me for performance reasons.

Answer 1

No, resizeing to a smaller size will never reallocate.

In case the container shrinks, all iterators, pointers and references to elements that have not been removed remain valid after the resize and refer to the same elements they were referring to before the call.

(From here)

Given that, we can be sure that a reallocation cannot have happened.