std::allocator_traits<Alloc>::allocate

 

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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>
	(1)
static pointer allocate( Alloc& a, size_type n );			(since C++11) (until C++20)
[[nodiscard]] static constexpr pointer allocate( Alloc& a, size_type n );			(since C++20)
		(2)
static pointer allocate( Alloc& a, size_type n,                          const_void_pointer hint );				(since C++11) (until C++20)
[[nodiscard]] static constexpr pointer allocate( Alloc& a, size_type n,                                                  const_void_pointer hint );				(since C++20)

Uses the allocator a to allocate n * sizeof(Alloc::value_type) bytes of uninitialized storage. An array of type Alloc::value_type[n] is created in the storage, but none of its elements are constructed.

1) Calls a.allocate(n).

2) Additionally passes memory locality hint hint. Calls a.allocate(n, hint) if possible. If not possible (e.g. a has no two-argument member function allocate), calls a.allocate(n).

Parameters

a	-	allocator to use
n	-	the number of objects to allocate storage for
hint	-	pointer to a nearby memory location

Return value

The pointer returned by the call to a.allocate(n).

Notes

Alloc::allocate was not required to create array object until P0593R6, which made using non-default allocator for std::vector and some other containers not well-defined according to a strict reading of the core language specification.

After calling allocate and before construction of elements, pointer arithmetic of Alloc::value_type* is well-defined within the allocated array, but the behavior is undefined if elements are accessed.

See also

allocate

allocates uninitialized storage (public member function of std::allocator<T>)