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C++ STL Containers Note

This post illustrates my studying upon STL containers in C++ standard categorized in its type.

Associative Container

STL Names Impl Note
std::set Red-black tree Contains a sorted set of unique objects
std::map Red-black tree Contains key-value pairs with unique keys.
std::multiset Red-black tree, B+Tree Contains a sorted set of objects but allowed multiple of equivalent objects.
std::multimap Red-black tree Contains key-value pairs but allowed equivalent of keys.

Unordered Associative Container

STL Names Impl Note
std::unordered_set hashmap with external linked-list to store elements Hashmap whose hashing function operates on the values directly. It allows only unique values (as keys)
std::unordered_map same Hashmap whose hashing function operates on keys. It allows only unique keys.
std::unordered_multiset same Same as std::unordered_set but allows equivalent of values as keys.
std::unordered_multimap same Same as std::unordered_map but allows euiqvalent of keys.

Sequence Container

STL Names Impl Note
std::array fixed-size array Based on top of fixed-size raw array but provide meta information accessible in object-oriented way i.e. size, back, front, or directly access to raw array via data.
std::vector growable with contiguous array Growable with contiguous array. Special note, std::vector<bool> is specialized template with subset feature of std::vector to provide optimized memory allocation and usage as it packs data as per 1-bit for bool data type; subset feature in this case refers to return by reference of individual element doesn't work as there is no addressable unit in term of bit but there is workaround to that by using std::vector<bool>::reference or auto &&var = boolVector[2] ref.
std::deque individually fixed-size allocated arrays with additional bookeeping It's shorted for double-ended queue which provides ability to do fast insertion and deletion at either end, with also fast random-access.
std::list doubly-linked list Provides fast insertion and deletion anywhere in the container. Fast random-access is not supported.
std::forward_list singly-linked list Similar to std::list but provides more space efficient storage when bidirectional iteration is not needed.

Container Adaptor

STL Names Impl Note
std::stack based on std::deque Provides LIFO (last-in, first-out) data structure. It acts as a wrapper, and only a specific set of functions on top of std::deque is provided. Thus it only provides push (from push_back), pop (from pop_back), and top (from back).
std::queue based on std::deque Provides FIFO (first-in, first-out) data structure. It acts as a wrapper, and only a specific set of functions on top of std::deque is provided. Thus it only provides push (from push_back), pop (from pop_back), top (from back), and front (from front).
std::priority_queue based on std::vector Provides constant in lookup of the largest (by default) element. It's similar to heap which we can manually manage via other STL functions i.e. std::make_heap, std::push_heap, and std::pop_heap but with benefit of not to accidentally invalidate the heap.



First published on Oct, 8, 2019






Written by Wasin Thonkaew
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