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In the programming language C++, unordered associative containers are a group of class templates in the C++ Standard Library that implement hash table variants. Being templates, they can be used to store arbitrary elements, such as integers or custom classes.
The containers are defined in headers named after the names of the containers, e.g. set is defined in header <set>.All containers satisfy the requirements of the Container concept, which means they have begin(), end(), size(), max_size(), empty(), and swap() methods.
hash_map hash_multimap similar to a set, multiset, map, or multimap, respectively, but implemented using a hash table; keys are not ordered, but a hash function must exist for the key type. These types were left out of the C++ standard; similar containers were standardized in C++11, but with different names (unordered_set and unordered_map).
Although std::map is typically implemented using a self-balancing binary search tree, C++11 defines a second map called std::unordered_map, which has the algorithmic characteristics of a hash table. This is a common vendor extension to the Standard Template Library (STL) as well, usually called hash_map , available from such implementations as ...
Threading Building Blocks provide concurrent unordered maps for C++ which allow concurrent insertion and traversal and are kept in a similar style to the C++11 std::unordered_map interface. Included within are the concurrent unordered multimaps, which allow multiple values to exist for the same key in a concurrent unordered map. [12]
The C++ Standard Library's associative containers (std::unordered_map and std::map) use operator[] to get the value associated to a key. If there is nothing associated to this key, it will construct it and value initialize [4] [unreliable source] [failed verification] the value. For simple types like int or float, the value initialization will ...
New insertion functions try_emplace and insert_or_assign for std::map and std::unordered_map key-value associative data structures [33] [34]
insert(e): First, a new node with a key and a priority is created. In addition, the node is assigned a number of levels, which dictates the size of the array of pointers. Then a search is performed to find the correct position where to insert the new node. The search starts from the first node and from the highest level.