std::allocator_traits::allocate - cppreference.com (original) (raw)

Defined in header
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).

[edit] Parameters

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

[edit] Return value

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

[edit] 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.

[edit] Example

[edit] See also

| | allocates uninitialized storage (public member function of std::allocator) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |