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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.
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 ...
A map, sometimes referred to as a dictionary, consists of a key/value pair. The key is used to order the sequence, and the value is somehow associated with that key. For example, a map might contain keys representing every unique word in a text and values representing the number of times that word appears in the text.
ECMAScript 2015 also added the Map data structure, which accepts arbitrary values as keys. [50] C++11 includes unordered_map in its standard library for storing keys and values of arbitrary types. [51] Go's built-in map implements a hash table in the form of a type. [52]
In Smalltalk, Objective-C, .NET, [20] Python, REALbasic, Swift, VBA and Delphi [21] they are called dictionaries; in Perl, Ruby and Seed7 they are called hashes; in C++, C#, Java, Go, Clojure, Scala, OCaml, Haskell they are called maps (see map (C++), unordered_map (C++), and Map); in Common Lisp and Windows PowerShell, they are called hash ...
<unordered_map> Added in C++11 and TR1. Provides the container class template std::unordered_map and std::unordered_multimap, hash tables. <unordered_set> Added in C++11 and TR1. Provides the container class template std::unordered_set and std::unordered_multiset. <vector> Provides the container class template std::vector, a dynamic array.
Additionally, concurrent hash maps are provided which build upon the concurrent unordered map and further allow concurrent erasure and contain built-in locking. [13] growt provides concurrent growing hash tables for C++ on the basis of the so-called folklore implementation. Based on this non-growing implementation, a variety of different ...
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). Other types of containers ...