Introduction

The sequential container has a lot in common, but each container has its special domain. Before I dive into the details, I provide an overview of all five sequential containers of the std namespace.

These are the sequential containers:

Criteria	Array	Vector	Deque	List	Forward List
Size	static	dynamic	dynamic	dynamic	dynamic
Implementation	static array	dynamic array	sequence of arrays	doubly linked list	singly linked list
Access	random	random	random	forward and backward	forward
Optimized for insert and delete at	—	end: O(1)	begin and end: O(1)	begin and end: O(1); arbitrary: O(1)	begin(1); arbitrary: O(1)
Memory reservation	—	yes	no	no	no
Release of memory	—	shrink_to_fit	shrink_to_fit	always	always
Strength	no memory allocation; minimal memory requirements	95% solution	insertion and deletion at the begin and end	insertion and deletion at an arbitrary position	fast insertion and deletion; minimal memory requirements
Weakness	no dynamic memory; memory allocation	Insertion and deletion; at an arbitrary position: O(n)	Insertion and deletion; at an arbitrary position: O(n)	no random access	no random access

The sequential containers

A few additional remarks to the table.

O(i) stands for the complexity (runtime) of an operation. So O(1) means that the runtime of an operation on a container is constant and is independent of the size of the container. Conversely, O(n) means that the runtime depends on the number of elements of the container. Now, what does that mean for a std::vector? The access time on an element is independent of the size of the std::vector, but the insertion or deletion of an arbitrary element with k-times more elements is k-times slower.

Although the random access on the elements of a std::vector has the same complexity O(1) as the random access on the element of a std::deque, that doesn’t mean, that both operations are equally fast.

The complexity guarantee O(1) for the insertion or deletion into a doubly (std::list) or singly linked list (std::forward_list) is only guaranteed if the iterator points to the right element.

ℹ️ std::string is like std::vector
Of course, std::string is no container of the standard template library. But from a behavioural point of view, it is like a sequential container, especially like a std::vector<char>. Therefore I will treat std::string as a std::vector<char>.