STL and most other containers value initialize new elements in common operations
vector::resize(size_type n) or
In some performance-sensitive environments, where vectors are used as a replacement for variable-size buffers for file or network operations, value initialization is a cost that is not negligible as elements are going to be overwritten by an external source shortly after new elements are added to the container.
Boost.Container offers two new members for
explicit container::container(size_type n, default_init_t) and
container::resize(size_type n, default_init_t), where new elements are constructed using