std::allocator_traits

 

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std::allocator_traits

Member functions

allocator_traits::allocate (C++11)

allocator_traits::allocate_at_least (C++23)

allocator_traits::deallocate (C++11)

allocator_traits::construct (C++11)

allocator_traits::destroy (C++11)

allocator_traits::max_size (C++11)

allocator_traits::select_on_container_copy_construction (C++11)

 

Defined in header <memory>
template< class Alloc > struct allocator_traits;		(since C++11)

The allocator_traits class template provides the standardized way to access various properties of Allocators. The standard containers and other standard library components access allocators through this template, which makes it possible to use any class type as an allocator, as long as the user-provided specialization of std::allocator_traits implements all required functionality.

A program that declares an explicit or partial specialization of std::allocator_traits is ill-formed, no diagnostic required.

(since C++23)

The default, non-specialized, std::allocator_traits contains the following members:

Member types

Type	Definition
allocator_type	Alloc
value_type	Alloc::value_type
pointer	Alloc::pointer if present, otherwise value_type*
const_pointer	Alloc::const_pointer if present, otherwise std::pointer_traits<pointer>::rebind<const value_type>
void_pointer	Alloc::void_pointer if present, otherwise std::pointer_traits<pointer>::rebind<void>
const_void_pointer	Alloc::const_void_pointer if present, otherwise std::pointer_traits<pointer>::rebind<const void>
difference_type	Alloc::difference_type if present, otherwise std::pointer_traits<pointer>::difference_type
size_type	Alloc::size_type if present, otherwise std::make_unsigned<difference_type>::type
propagate_on_container_copy_assignment	Alloc::propagate_on_container_copy_assignment if present, otherwise std::false_type
propagate_on_container_move_assignment	Alloc::propagate_on_container_move_assignment if present, otherwise std::false_type
propagate_on_container_swap	Alloc::propagate_on_container_swap if present, otherwise std::false_type
is_always_equal	Alloc::is_always_equal if present, otherwise std::is_empty<Alloc>::type

Member alias templates

Type	Definition
rebind_alloc<T>	Alloc::rebind<T>::other if present, otherwise Alloc<T, Args> if this Alloc is Alloc<U, Args>
rebind_traits<T>	std::allocator_traits<rebind_alloc<T>>

Member functions

allocate [static]	allocates uninitialized storage using the allocator (public static member function)
allocate_at_least [static] (C++23)	allocates storage at least as large as the requested size via an allocator (public static member function)
deallocate [static]	deallocates storage using the allocator (public static member function)
construct [static]	constructs an object in the allocated storage (function template)
destroy [static]	destructs an object stored in the allocated storage (function template)
max_size [static]	returns the maximum object size supported by the allocator (public static member function)
select_on_container_copy_construction [static]	obtains the allocator to use after copying a standard container (public static member function)

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 2108	C++11	there was no way to show an allocator is stateless	is_always_equal provided

See also

allocator	the default allocator (class template)
scoped_allocator_adaptor (C++11)	implements multi-level allocator for multi-level containers (class template)
pointer_traits (C++11)	provides information about pointer-like types (class template)