std::scoped_allocator_adaptor<OuterAlloc,InnerAlloc...>::construct

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Dynamic memory management

Uninitialized memory algorithms uninitialized_copy uninitialized_fill uninitialized_move (C++17) uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17) destroy_at (C++17) voidify (C++20) uninitialized_copy_n (C++11) uninitialized_fill_n uninitialized_move_n (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17) construct_at (C++20) Constrained uninitialized memory algorithms ranges::uninitialized_copy (C++20) ranges::uninitialized_fill (C++20) ranges::uninitialized_move (C++20) ranges::construct_at (C++20) ranges::destroy (C++20) ranges::destroy_n (C++20) ranges::destroy_at (C++20) ranges::uninitialized_copy_n (C++20) ranges::uninitialized_fill_n (C++20) ranges::uninitialized_move_n (C++20) ranges::uninitialized_default_construct (C++20) ranges::uninitialized_value_construct (C++20) ranges::uninitialized_default_construct_n (C++20)   ranges::uninitialized_value_construct_n (C++20) Allocators allocator allocator_traits (C++11) allocation_result (C++23) allocator_arg (C++11) uses_allocator (C++11) uses_allocator_construction_args (C++20) make_obj_using_allocator (C++20) uninitialized_construct_using_allocator (C++20) scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) Memory resources pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17)   pmr::monotonic_buffer_resource (C++17) pmr::pool_options (C++17) Garbage collection support declare_reachable (C++11)(until C++23) undeclare_reachable (C++11)(until C++23) declare_no_pointers (C++11)(until C++23) undeclare_no_pointers (C++11)(until C++23) pointer_safety (C++11)(until C++23) get_pointer_safety (C++11)(until C++23) Uninitialized storage raw_storage_iterator (until C++20*) get_temporary_buffer (until C++20*) return_temporary_buffer (until C++20*) Explicit lifetime management start_lifetime_asstart_lifetime_as_array (C++23)(C++23)

Smart pointers unique_ptr (C++11) shared_ptr (C++11) weak_ptr (C++11) auto_ptr (until C++17*) owner_less (C++11) owner_less<void> (C++17) owner_hash (C++26) owner_equal (C++26) enable_shared_from_this (C++11) bad_weak_ptr (C++11) default_delete (C++11) out_ptr_t (C++23) inout_ptr_t (C++23) Low level memory management operator new operator new[] operator delete operator delete[] get_new_handler (C++11) set_new_handler launder (C++17) bad_alloc bad_array_new_length (C++11) nothrow_t align_val_t (C++17) destroying_delete_t (C++20) new_handler nothrow Miscellaneous pointer_traits (C++11) to_address (C++20) addressof (C++11) align (C++11) assume_aligned (C++20) C Library malloc calloc realloc    aligned_alloc (C++17) free

 

std::scoped_allocator_adaptor

Member functions

scoped_allocator_adaptor::scoped_allocator_adaptor

scoped_allocator_adaptor::~scoped_allocator_adaptor

scoped_allocator_adaptor::operator=

scoped_allocator_adaptor::inner_allocator

scoped_allocator_adaptor::outer_allocator

scoped_allocator_adaptor::allocate

scoped_allocator_adaptor::deallocate

scoped_allocator_adaptor::max_size

scoped_allocator_adaptor::construct

scoped_allocator_adaptor::destroy

scoped_allocator_adaptor::select_on_container_copy_construction

scoped_allocator_adaptor::outermost scoped_allocator_adaptor::outermost-construct scoped_allocator_adaptor::outermost-destroy

Non-member functions

operator==operator!= (until C++20)

Deduction guides(C++17)

 

Defined in header <scoped_allocator>
template< class T, class... Args > void construct( T* p, Args&&... args );	(1)
template< class T1, class T2, class... Args1, class... Args2 > void construct( std::pair<T1, T2>* p, std::piecewise_construct_t,                 std::tuple<Args1...> x, std::tuple<Args2...> y );	(2)	(until C++20)
template< class T1, class T2 > void construct( std::pair<T1, T2>* p );	(3)	(until C++20)
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, U&& x, V&& y );	(4)	(until C++20)
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, const std::pair<U, V>& xy );	(5)	(until C++20)
template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, std::pair<U, V>&& xy );	(6)	(until C++20)
Helper function templates
template < class T, class... Args > std::tuple</* see below */> /*concat-args*/( std::tuple<Args...>&& tup );	(7)	(exposition only*) (until C++20)

Constructs an object in allocated, but not initialized storage pointed to by p using the outer allocator and the provided constructor arguments. If the object is of a type that itself uses allocators, or if it is std::pair(until C++20), passes the inner allocator down to the constructed object.

1) Constructs an object of type T by uses-allocator construction at the uninitialized memory location indicated by p using the outermost allocator.

Given std::uses_allocator<T, inner_allocator_type>::value as uses_inner: If uses_inner is false and std::is_constructible<T, Args...>::value is true, calls outermost-construct (p, std::forward<Args>(args)...). Otherwise, if uses_inner and std::is_constructible<T, std::allocator_arg_t,                       inner_allocator_type&,                       Args...>::value are both true, calls outermost-construct (p, std::allocator_arg,                     inner_allocator(),                     std::forward<Args>(args)...). Otherwise, if uses_inner and std::is_constructible<T, Args..., inner_allocator_type&>::value are both true, calls outermost-construct (p, std::forward<Args>(args)..., inner_allocator()). Otherwise, the program is ill-formed. This overload participates in overload resolution only if T is not a specialization of std::pair.

(until C++20)

Equivalent to std::apply (     [p, this](auto&&... newargs)     {         outermost-construct             (p, std::forward<decltype(newargs)>(newargs)...);     },     std::uses_allocator_construction_args         (inner_allocator(), std::forward<Args>(args)...) ); .

(since C++20)

2-6) Constructs a std::pair object by uses-allocator construction at the uninitialized memory location indicated by p using the outermost allocator.

2) Let xprime be concat-args <T1>(std::move(x)), yprime be concat-args <T2>(std::move(y)), calls outermost-construct (p, std::piecewise_construct, std::move(xprime), std::move(yprime)).

3) Equivalent to construct(p, std::piecewise_construct, std::tuple<>(), std::tuple<>());.

4-6) Equivalent to construct(p, std::piecewise_construct,
          std::forward_as_tuple(xarg), std::forward_as_tuple(yarg));, where xarg and yarg are defined as follows:

Overload	xarg	yarg
(4)	std::forward<U>(x)	std::forward<V>(y)
(5)	xy.first	xy.second
(6)	std::forward<U>(xy.first)	std::forward<V>(xy.second)

7) Merges the arguments contained in tup and additional arguments required by uses-allocator construction of an object of type T.

Given std::uses_allocator<T, inner_allocator_type>::value as uses_inner:

• If uses_inner is false and std::is_constructible<T, Args...>::value is true, returns std::tuple<Args&&...>(std::move(tup)).
• Otherwise, if uses_inner and std::is_constructible<T, std::allocator_arg_t,
                        inner_allocator_type&,
                        Args...>::value are both true, returns std::tuple_cat(std::tuple<std::allocator_arg_t, inner_allocator_type&>
                     (std::allocator_arg, inner_allocator()),
                 std::tuple<Args&&...>(std::move(tup))).
• Otherwise, if uses_inner and std::is_constructible<T, Args..., inner_allocator_type&>::value are both true, returns std::tuple_cat(std::tuple<Args&&...>(std::move(tup)),
                 std::tuple<inner_allocator_type&>(inner_allocator()).
• Otherwise, the program is ill-formed.

Parameters

p	-	pointer to allocated, but not initialized storage
args	-	the constructor arguments to pass to the constructor of T
x	-	the constructor arguments to pass to the constructor of T1
y	-	the constructor arguments to pass to the constructor of T2
xy	-	the pair whose two members are the constructor arguments for T1 and T2
tup	-	the arguments to be merged

Notes

This function is called (through std::allocator_traits) by any allocator-aware object, such as std::vector, that was given a std::scoped_allocator_adaptor as the allocator to use. Since inner_allocator_type is itself a specialization of std::scoped_allocator_adaptor, this function will also be called when the allocator-aware objects constructed through this function start constructing their own members.

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 2203	C++11	inner allocators were obtained by value-initializing an inner_allocator_type object	obtained by calling inner_allocator()
LWG 2511 (P0475R1)	C++11	concat-args might copy elements of std::tuples	eliminated all element copy operations
LWG 2586	C++11	only constructions from inner_allocator_type rvalues were checked	checks constructions from non-const inner_allocator_type lvalues instead
LWG 2975	C++11	overload (1) was not constrained	constrained to refuse std::pair

See also

construct [static]	constructs an object in the allocated storage (function template)
construct (until C++20)	constructs an object in allocated storage (public member function of std::allocator<T>)