Associative Containers
Associative containers are containers that allow for the fast lookup of elements. Additionally, the elements are always kept in a sorted order. The order is determined by the value of the element and a comparison function. The comparison function is called a comparator, and by default this is the operator<, although the user can supply a Functor (function object) as a parameter to specify how the elements should be compared. The <functional> header contains many such objects that can be used to sort the associative containers, like std::less or std::less.
Figure 5.10: Table presenting associative containers and their descriptions
Typically, associative containers are implemented as variations of binary trees, providing fast element lookup by exploiting the logarithmic complexity of the underlying structure.
Set and Multiset
A Set is a container that contains a unique group of sorted elements. A Multiset is similar to Set, but it allows duplicate elements:
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