Will a call to std::vector::clear() set std::vector::capacity() to zero?

It is specified that std::vector<T>::clear() affects the size. It might not affect the capacity. For resetting the capacity, use the swap trick:

    std::vector<int> v1;

    // somehow increase capacity

    std::vector<int>().swap(v1);

Note: Since this old answer is still getting upvotes (thus people read it), I feel the need to add that C++11 has added std::vector<...>::shrink_to_fit(), which requests the vector to remove unused capacity.