std::allocator_traits<Alloc>:: allocate

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C++
Dynamic memory management
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Allocators
Garbage collection support
(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::allocator_traits
Defined in header <memory>
static pointer allocate ( Alloc & a, size_type n ) ;
(1) (since C++11)
(constexpr since C++20)
static pointer allocate ( Alloc & a, size_type n, const_void_pointer hint ) ;
(2) (since C++11)
(constexpr 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.

Example

This section is incomplete
Reason: no example

See also

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