Associative containers
Associative containers store data in a sorted fashion, unlike the sequence containers. Hence, the order in which the data is inserted will not be retained by the associative containers. Associative containers are highly efficient in searching a value with O( log n ) runtime complexity. Every time a new value gets added to the container, the container will reorder the values stored internally if required.
The STL supports the following types of associative containers:
- Set
- Map
- Multiset
- Multimap
- Unordered set
- Unordered multiset
- Unordered map
- Unordered multimap
Associative containers organize the data as key-value pairs. The data will be sorted based on the key for random and faster access. Associative containers come in two flavors:
- Ordered
- Unordered
The following associative containers come under ordered containers, as they are ordered/sorted in a particular fashion. Ordered associative containers generally use some form of Binary Search Tree (BST); usually, a red-black tree is used to store the data:
- Set
- Map
- Multiset
- Multimap
The following associative containers come under unordered containers, as they are not ordered in any particular fashion and they use hash tables:
- Unordered Set
- Unordered Map
- Unordered Multiset
- Unordered Multimap
Let's understand the previously mentioned containers with examples in the following subsections.