24 Containers library [containers]

24.2 Requirements [container.requirements]

24.2.2 General containers [container.requirements.general]

24.2.2.1 Introduction [container.intro.reqmts]

In subclause [container.requirements.general],

(1.1)
X denotes a container class containing objects of type T,
(1.2)
a denotes a value of type X,
(1.3)
b and c denote values of type (possibly const) X,
(1.4)
i and j denote values of type (possibly const) X::iterator,
(1.5)
u denotes an identifier,
(1.6)
v denotes an lvalue of type (possibly const) X or an rvalue of type const X,
(1.7)
s and t denote non-const lvalues of type X, and
(1.8)
rv denotes a non-const rvalue of type X.

The following exposition-only concept is used in the definition of containers: template<class R, class T> concept container-compatible-range = // exposition only ranges::input_range<R> && convertible_to<ranges::range_reference_t<R>, T>;

24.2.2.2 Container requirements [container.reqmts]

A type X meets the container requirements if the following types, statements, and expressions are well-formed and have the specified semantics.

typename X::value_type

Result: T

Preconditions: T is Cpp17Erasable from X (see [container.alloc.reqmts], below).

typename X::reference

Result: T&

typename X::const_reference

Result: const T&

typename X::iterator

Result: A type that meets the forward iterator requirements ([forward.iterators]) with value type T.

The type X::iterator is convertible to X::const_iterator.

typename X::const_iterator

Result: A type that meets the requirements of a constant iterator and those of a forward iterator with value type T.

typename X::difference_type

Result: A signed integer type, identical to the difference type of X::iterator and X::const_iterator.

typename X::size_type

Result: An unsigned integer type that can represent any non-negative value of X::difference_type.

X u;
X u = X();

Postconditions: u.empty()

Complexity: Constant.

X u(v);
X u = v;

Preconditions: T is Cpp17CopyInsertable into X (see below).

Postconditions: u == v.

Complexity: Linear.

X u(rv);
X u = rv;

Postconditions: u is equal to the value that rv had before this construction.

Complexity: Linear for array and constant for all other standard containers.

t = v;

Result: X&.

Postconditions: t == v.

Complexity: Linear.

t = rv

Result: X&.

Effects: All existing elements of t are either move assigned to or destroyed.

Postconditions: If t and rv do not refer to the same object, t is equal to the value that rv had before this assignment.

Complexity: Linear.

a.~X()

Result: void.

Effects: Destroys every element of a; any memory obtained is deallocated.

Complexity: Linear.

b.begin()

Result: iterator; const_iterator for constant b.

Returns: An iterator referring to the first element in the container.

Complexity: Constant.

b.end()

Result: iterator; const_iterator for constant b.

Returns: An iterator which is the past-the-end value for the container.

Complexity: Constant.

b.cbegin()