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std::allocator_traits::allocate(3) C++ Standard Libary std::allocator_traits::allocate(3)


std::allocator_traits::allocate - std::allocator_traits::allocate


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

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)


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)


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 actually
well-defined according to 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>)