std::unordered_map

template<
    class Key,
    class T,
    class Hash = std::hash<Key>,
    class KeyEqual = std::equal_to<Key>,
    class Allocator = std::allocator< std::pair<const Key, T> >
> class unordered_map;

Unordered map is an associative container that contains key-value pairs with unique keys. Search, insertion, and removal of elements have average constant-time complexity.

Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its key. This allows fast access to individual elements, since once hash is computed, it refers to the exact bucket the element is placed into.

std::unordered_map meets the requirements of Container, AllocatorAwareContainer, UnorderedAssociativeContainer.

Iterator invalidation

Notes

• The swap functions do not invalidate any of the iterators inside the container, but they do invalidate the iterator marking the end of the swap region.
• References and pointers to either key or data stored in the container are only invalidated by erasing that element, even when the corresponding iterator is invalidated.

Member types

Member functions

Non-member functions