std::allocator<T>::allocate (3) - Linux Manuals

std::allocator<T>::allocate: std::allocator<T>::allocate

NAME

std::allocator<T>::allocate - std::allocator<T>::allocate

Synopsis

pointer allocate( size_type n, const void * hint = 0 ); (1) (until C++17)
                                                            (since C++17)
T* allocate( std::size_t n, const void * hint); (1) (deprecated)
                                                            (removed in C++20)
T* allocate( std::size_t n ); (since C++17)
                                                        (2) (until C++20)
[[nodiscard]] T* allocate( std::size_t n ); (since C++20)

Allocates n * sizeof(T) bytes of uninitialized storage by calling ::operator_new(std::size_t)
or ::operator_new(std::size_t, std::align_val_t)
(since C++17), but it is unspecified when and how this function is called. The pointer hint may be used to provide locality of reference: the allocator, if supported by the implementation, will attempt to allocate the new memory block as close as possible to hint.

Parameters

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

Return value

Pointer to the first byte of a memory block suitably aligned and sufficient to hold an array of n objects of type T.

Exceptions

Throws std::bad_alloc if allocation fails.

Notes

The "unspecified when and how" wording makes it possible to combine_or_optimize_away_heap_allocations made by the standard library containers, even though such optimizations are disallowed for direct calls to ::operator new. For example, this is implemented by libc++ ([1] and [2])