Standard Template Library Programmer's Guide

Category: containers

Component type: concept

Description

A Back Insertion Sequence is a Sequence where it is possible to append an element to the end, or to access the last element, in amortized constant time. Back Insertion Sequences have special member functions as a shorthand for those operations.

Refinement of

Sequence

Associated types

None, except for those of Sequence.

Notation

X A type that is a model of Back Insertion Sequence

a Object of type X

T The value type of X

t Object of type T

Valid expressions

In addition to the expressions defined in Sequence, the following expressions must be valid.

Name	Expression	Type requirements	Return type
Back	a.back()		reference if a is mutable, otherwise const_reference.
Push back	a.push_back(t)	a is mutable.	void
Pop back	a.pop_back()	a is mutable.	void

Expression semantics

Name	Expression	Precondition	Semantics	Postcondition
Back	a.back()	!a.empty()	Equivalent to *(--a.end()).
Push back	a.push_back(t)		Equivalent to a.insert(a.end(), t) a.size is incremented by 1.	a.back() is a copy of t.
Pop back	a.pop_back()	!a.empty()	Equivalent to a.erase(--a.end())	a.size() is decremented by 1.

Complexity guarantees

Back, push back, and pop back are amortized constant time. [1]

Invariants

Symmetry of push and pop

push_back() followed by pop_back() is a null operation.

Models

vector

list

deque

Notes

[1] This complexity guarantee is the only reason that back(), push_back(), and pop_back() are defined: they provide no additional functionality. Not every sequence must define these operations, but it is guaranteed that they are efficient if they exist at all.

See also

Container, Sequence, Front Insertion Sequence, vector, deque, list