C++ named requirements: AllocatorAwareContainer (since C++11)

An AllocatorAwareContainer is a Container that holds an instance of an Allocator and uses that instance in all its member functions to allocate and deallocate memory and to construct and destroy objects in that memory (such objects may be container elements, nodes, or, for unordered containers, bucket arrays), except that std::basic_string specializations do not use the allocators for construction/destruction of their elements(since C++23).

The following rules apply to container construction:

• Copy constructors of AllocatorAwareContainers obtain their instances of the allocator by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction on the allocator of the container being copied.
• Move constructors obtain their instances of allocators by move-constructing from the allocator belonging to the old container.
• All other constructors take a const allocator_type& parameter.

The only way to replace an allocator is copy-assignment, move-assignment, and swap:

• Copy-assignment will replace the allocator only if std::allocator_traits<allocator_type>::propagate_on_container_copy_assignment::value is true.
• Move-assignment will replace the allocator only if std::allocator_traits<allocator_type>::propagate_on_container_move_assignment::value is true.
• Swap will replace the allocator only if std::allocator_traits<allocator_type>::propagate_on_container_swap::value is true. Specifically, it will exchange the allocator instances through an unqualified call to the non-member function swap, see Swappable.

Note: swapping two containers with unequal allocators if propagate_on_container_swap is false is undefined behavior.

• The accessor get_allocator() obtains a copy of the allocator that was used to construct the container or installed by the most recent allocator replacement operation.

Требования

Легенда

Типы

Члены-функции и операторы

Примечания

Контейнеры, учитывающие алокатор, всегда вызывают std::allocator_traits<A>::construct(m, p, args) для построения объекта типа T в p с использованием args, при m == get_allocator(). По умолчанию construct в std::allocator вызовет ::new((void*)p) T(args)(до C++20)std::allocator не имеет члена construct и std::construct_at(p, args) вызывается при построении элементов(с C++20), но специализированные алокаторы могут выбрать другое определение.

Стандартная библиотека

Все контейнеры стандартной библиотеки, кроме std::array являются AllocatorAwareContainers:

• std::basic_string
• std::deque
• std::forward_list
• std::list
• std::vector
• std::map
• std::multimap
• std::set
• std::multiset
• std::unordered_map
• std::unordered_multimap
• std::unordered_set
• std::unordered_multiset

Отчеты об ошибках

Следующие отчеты об ошибках, изменяющие поведение, были применены ретроактивно к ранее опубликованным стандартам C++.