C++ named requirements: Container

A Container is an object used to store other objects and taking care of the management of the memory used by the objects it contains.

Requirements

• C container type;
• T element type;
• a, b objects of type C.
• rv a prvalue expression of type C.

Types

name	type	notes
value_type	T	Erasable
reference	T&
const_reference	const T&
iterator	iterator pointing to T	LegacyForwardIterator convertible to const_iterator
const_iterator	constant iterator pointing to T	LegacyForwardIterator
difference_type	signed integer	must be the same as iterator_traits::difference_type for iterator and const_iterator
size_type	unsigned integer	large enough to represent all positive values of difference_type

Methods and operators

expression	return type	semantics	conditions	complexity
C()	C	creates an empty container	Post: C().empty() == true	Constant
C(a)	C	creates a copy of a	Pre: T must be CopyInsertable Post: a == C(a)	Linear
C(rv)(since C++11)	C	moves rv	Post: equal to the value rv had before this construction	Constant[1]
a = b	C&	destroys or copy-assigns all elements of a from elements of b	Post: a == b	Linear
a = rv	C&	destroys or move-assigns all elements of a from elements of rv	Post: if a and rv do not refer the same object, a is equal to the value rv had before this assignment	Linear
a.~C()	void	destroys all elements of a and frees all memory		Linear
a.begin()	(const_)iterator	Iterator to the first element of a		Constant
a.end()	(const_)iterator	Iterator to one past the last element of a		Constant
a.cbegin()(since C++11)	const_iterator	const_cast<const C&>(a).begin()		Constant
a.cend()(since C++11)	const_iterator	const_cast<const C&>(a).end()		Constant
a == b	convertible to bool	a.size() == b.size() && std::equal(a.begin(), a.end(), b.begin()) (until C++14)std::equal(a.begin(), a.end(), b.begin(), b.end()) (since C++14)	Pre: T must be EqualityComparable	Constant[2] if a.size() != b.size(), linear otherwise
a != b	convertible to bool	!(a == b)		Linear
a.swap(b)	void	exchanges the values of a and b		Constant[1][3]
swap(a, b)	void	a.swap(b)		Constant[1]
a.size()	size_type	std::distance(a.begin(), a.end())		Constant[3]
a.max_size()	size_type	b.size() where b is the largest possible container		Constant[3]
a.empty()	convertible to bool	a.begin() == a.end()		Constant
notes
Linear for std::array always linear for std::forward_list (until C++11) Not strictly constant

Given.

• i and j, objects of a container's iterator type,

in the expressions i == j, i != j, i < j, i <= j, i >= j, i > j, i - j, either or both may be replaced by an object of the container's const_iterator type referring to the same element with no change in semantics.

Container data races

see container thread safety.

Other requirements

C

• DefaultConstructible
• CopyConstructible
• EqualityComparable
• Swappable

T

• CopyInsertable
• EqualityComparable
• Destructible

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 179	C++98	iterator and const_iterator types might be incomparable	required to be comparable
LWG 2263	C++11	resolution of LWG179 was accidentally dropped in C++11	restored
LWG 2839	C++11	self move assignment of standard containers was not allowed	allowed but the result is unspecifed

See also

C++ documentation for Containers library