[allocator.members]

# 20 Memory management library [[mem]](./#mem)

## 20.2 Memory [[memory]](memory#allocator.members)

### 20.2.10 The default allocator [[default.allocator]](default.allocator#allocator.members)

#### 20.2.10.2 Members [allocator.members]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1994)

Except for the destructor, member functions of the default allocator shall not introduce
data races ([[intro.multithread]](intro.multithread "6.10.2 Multi-threaded executions and data races")) as a result of concurrent calls to those member
functions from different threads[.](#1.sentence-1)

Calls to these functions that allocate or deallocate a
particular unit of storage shall occur in a single total order, and each such
deallocation call shall happen before the next allocation (if any) in this order[.](#1.sentence-2)

[🔗](#lib:allocate,allocator)

`constexpr T* allocate(size_t n);
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2007)

*Mandates*: T is not an incomplete type ([[basic.types.general]](basic.types.general#term.incomplete.type "6.9.1 General"))[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2011)

*Returns*: A pointer to the initial element of an array of n T[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2015)

*Throws*: bad_array_new_length ifnumeric_limits<size_t>​::​max() / sizeof(T) < n, orbad_alloc if the storage cannot be obtained[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2021)

*Remarks*: The storage for the array
is obtained by calling ​::​operator new ([[new.delete]](new.delete "17.6.3 Storage allocation and deallocation")),
but it is unspecified when or how often this
function is called[.](#5.sentence-1)

This function starts the lifetime of the array object,
but not that of any of the array elements[.](#5.sentence-2)

[🔗](#lib:allocate_at_least,allocator)

`constexpr allocation_result<T*> allocate_at_least(size_t n);
`

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2037)

*Mandates*: T is not an incomplete type ([[basic.types.general]](basic.types.general#term.incomplete.type "6.9.1 General"))[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2041)

*Returns*: allocation_result<T*>{ptr, count},
where ptr is a pointer to
the initial element of an array of count T andcount ≥ n[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2048)

*Throws*: bad_array_new_length if numeric_limits<size_t>​::​max() / sizeof(T) < n,
or bad_alloc if the storage cannot be obtained[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2054)

*Remarks*: The storage for the array is obtained by calling ​::​operator new,
but it is unspecified when or how often this function is called[.](#9.sentence-1)

This function starts the lifetime of the array object,
but not that of any of the array elements[.](#9.sentence-2)

[🔗](#lib:deallocate,allocator)

`constexpr void deallocate(T* p, size_t n);
`

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2068)

*Preconditions*: 

- [(10.1)](#10.1)

  If p is memory that was obtained by a call to allocate_at_least,
let ret be the value returned andreq be the value passed as the first argument to that call[.](#10.1.sentence-1)
  p is equal to ret.ptr andn is a value such that req ≤ n ≤ ret.count[.](#10.1.sentence-2)

- [(10.2)](#10.2)

  Otherwise, p is a pointer value obtained from allocate[.](#10.2.sentence-1)
  n equals the value passed as the first argument
to the invocation of allocate which returned p[.](#10.2.sentence-2)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2083)

*Effects*: Deallocates the storage referenced by p[.](#11.sentence-1)

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2087)

*Remarks*: Uses​::​operator delete ([[new.delete]](new.delete "17.6.3 Storage allocation and deallocation")),
but it is unspecified
when this function is called[.](#12.sentence-1)