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Unordered associative containers (C++)
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<p>In the programming language <a href="/facts/C%252B%252B/Et0F2qn9">C++</a>, unordered associative containers are a group of class templates in the <a href="/facts/C%252B%252B_Standard_Library/A5vQNSAD">C++ Standard Library</a> that implement <a href="/facts/Hash_table/Ht4ptDPF">hash table</a> variants. Being <a href="/facts/Template_(programming)/TXEqGy7R">templates</a>, they can be used to store arbitrary elements, such as integers or custom classes. The following containers are defined in the current revision of the C++ standard: unordered_set, unordered_map, unordered_multiset, unordered_multimap. Each of these containers differ only on constraints placed on their elements. </p><p>The unordered associative containers are similar to the <a href="/facts/Associative_containers_(C%252B%252B)/sILq4lSq">associative containers</a> in the C++ Standard Library but have different constraints. As their name implies, the elements in the unordered associative containers are not <a href="/facts/Well_ordering/GrWEBWlW">ordered</a>. This is due to the use of hashing to store objects. The containers can still be <a href="/facts/Iterator/f0HhTBWz">iterated</a> through like a regular associative container. </p>