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std::pmr::polymorphic_allocator

From cppreference.com
< cpp‎ | memory
 
C++
 
Memory management library
(exposition only*)
Allocators
(C++11)
(C++23)
(C++11)
pmr::polymorphic_allocator
(C++17)
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Memory resources
Uninitialized storage (until C++20)
(until C++20*)
(until C++20*)
(until C++20*)

Garbage collector support (until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
 
std::pmr::polymorphic_allocator
 
Defined in header <memory_resource>
template< class T >
class polymorphic_allocator;
 (since C++17)
(until C++20)
template< class T = std::byte >
class polymorphic_allocator;
 (since C++20)

The class template std::pmr::polymorphic_allocator is an Allocator which exhibits different allocation behavior depending upon the std::pmr::memory_resource from which it is constructed. Since memory_resource uses runtime polymorphism to manage allocations, different container instances with polymorphic_allocator as their static allocator type are interoperable, but can behave as if they had different allocator types.

All specializations of polymorphic_allocator meet the allocator completeness requirements.

The polymorphic_allocator::construct member function does uses-allocator construction, so that the elements of a container using a polymorphic_allocator will use that same allocator for their own allocations. For example, a std::pmr::vector<std::pmr::string> will use the same memory_resource for the vector's storage and each string's storage.

For non-polymorphic allocators, similar propagation can be achieved with the help of std::scoped_allocator_adaptor.

Contents

[edit] Member types

Member type definition
value_type T

[edit] Member functions

 constructs a polymorphic_allocator
(public member function) [edit]
(destructor)
(implicitly declared)
 implicitly declared destructor
(public member function) [edit]
operator=
[deleted]
 copy assignment operator is deleted
(public member function) [edit]
Public member functions
allocate memory
(public member function) [edit]
deallocate memory
(public member function) [edit]
constructs an object in allocated storage
(public member function) [edit]
(deprecated in C++20)(undeprecated in C++26)
 destroys an object in allocated storage
(public member function) [edit]
(C++20)
 allocate raw aligned memory from the underlying resource
(public member function) [edit]
(C++20)
 free raw memory obtained from allocate_bytes
(public member function) [edit]