20 Memory management library [mem]

20.4 Memory resources [mem.res]

20.4.3 Class template polymorphic_allocator [mem.poly.allocator.class] Member functions [mem.poly.allocator.mem]

[[nodiscard]] Tp* allocate(size_t n);
Effects: If numeric_limits<size_t>​::​max() / sizeof(Tp) < n, throws bad_array_new_length.
Otherwise equivalent to: return static_cast<Tp*>(memory_rsrc->allocate(n * sizeof(Tp), alignof(Tp)));
void deallocate(Tp* p, size_t n);
Preconditions: p was allocated from a memory resource x, equal to *memory_rsrc, using x.allocate(n * sizeof(Tp), alignof(Tp)).
Effects: Equivalent to memory_rsrc->deallocate(p, n * sizeof(Tp), alignof(Tp)).
Throws: Nothing.
[[nodiscard]] void* allocate_bytes(size_t nbytes, size_t alignment = alignof(max_align_t));
Effects: Equivalent to: return memory_rsrc->allocate(nbytes, alignment);
[Note 1: 
The return type is void* (rather than, e.g., byte*) to support conversion to an arbitrary pointer type U* by static_cast<U*>, thus facilitating construction of a U object in the allocated memory.
— end note]
void deallocate_bytes(void* p, size_t nbytes, size_t alignment = alignof(max_align_t));
Effects: Equivalent to memory_rsrc->deallocate(p, nbytes, alignment).
template<class T> [[nodiscard]] T* allocate_object(size_t n = 1);
Effects: Allocates memory suitable for holding an array of n objects of type T, as follows:
  • if numeric_limits<size_t>​::​max() / sizeof(T) < n, throws bad_array_new_length,
  • otherwise equivalent to: return static_cast<T*>(allocate_bytes(n*sizeof(T), alignof(T)));
[Note 2: 
T is not deduced and must therefore be provided as a template argument.
— end note]
template<class T> void deallocate_object(T* p, size_t n = 1);
Effects: Equivalent to deallocate_bytes(p, n*sizeof(T), alignof(T)).
template<class T, class... CtorArgs> [[nodiscard]] T* new_object(CtorArgs&&... ctor_args);
Effects: Allocates and constructs an object of type T, as follows.

Equivalent to: T* p = allocate_object<T>(); try { construct(p, std::forward<CtorArgs>(ctor_args)...); } catch (...) { deallocate_object(p); throw; } return p;
[Note 3: 
T is not deduced and must therefore be provided as a template argument.
— end note]
template<class T> void delete_object(T* p);
Effects: Equivalent to: destroy(p); deallocate_object(p);
template<class T, class... Args> void construct(T* p, Args&&... args);
Mandates: Uses-allocator construction of T with allocator *this (see [allocator.uses.construction]) and constructor arguments std​::​forward<Args>(args)... is well-formed.
Effects: Construct a T object in the storage whose address is represented by p by uses-allocator construction with allocator *this and constructor arguments std​::​forward<Args>(args)....
Throws: Nothing unless the constructor for T throws.
template<class T> void destroy(T* p);
Effects: Equivalent to p->~T().
polymorphic_allocator select_on_container_copy_construction() const;
Returns: polymorphic_allocator().
[Note 4: 
The memory resource is not propagated.
— end note]
memory_resource* resource() const;
Returns: memory_rsrc.