[ptr.align]

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

## 20.2 Memory [[memory]](memory#ptr.align)

### 20.2.5 Pointer alignment [ptr.align]

[🔗](#lib:align)

`void* align(size_t alignment, size_t size, void*& ptr, size_t& space);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L946)

*Preconditions*: 

- [(1.1)](#1.1)

alignment is a power of two

- [(1.2)](#1.2)

ptr represents the address of contiguous storage of at leastspace bytes

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L957)

*Effects*: If it is possible to fit size bytes
of storage aligned by alignment into the buffer pointed to byptr with length space, the function updatesptr to represent the first possible address of such storage
and decreases space by the number of bytes used for alignment[.](#2.sentence-1)

Otherwise, the function does nothing[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L966)

*Returns*: A null pointer if the requested aligned buffer
would not fit into the available space, otherwise the adjusted value
of ptr[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L972)

[*Note [1](#note-1)*:

The function updates its ptr and space arguments so that it can be called repeatedly
with possibly different alignment and size arguments for the same buffer[.](#4.sentence-1)

— *end note*]

[🔗](#lib:assume_aligned)

`template<size_t N, class T>
  constexpr T* assume_aligned(T* ptr);
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L988)

*Mandates*: N is a power of two[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L992)

*Preconditions*: ptr points to an object X of
a type similar ([[conv.qual]](conv.qual "7.3.6 Qualification conversions")) to T,
where X has alignment N ([[basic.align]](basic.align "6.8.3 Alignment"))[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L998)

*Returns*: ptr[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1002)

*Throws*: Nothing[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1006)

[*Note [2](#note-2)*:

The alignment assumption on an object X expressed by a call to assume_aligned might result in generation of more efficient code[.](#9.sentence-1)

It is up to the program to ensure that the assumption actually holds[.](#9.sentence-2)

The call does not cause the implementation to verify or enforce this[.](#9.sentence-3)

An implementation might only make the assumption
for those operations on X that access X through the pointer returned by assume_aligned[.](#9.sentence-4)

— *end note*]

[🔗](#lib:is_sufficiently_aligned)

`template<size_t Alignment, class T>
  bool is_sufficiently_aligned(T* ptr);
`

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1026)

*Preconditions*: p points to
an object X of a type similar ([[conv.qual]](conv.qual "7.3.6 Qualification conversions")) to T[.](#10.sentence-1)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1031)

*Returns*: true if X has alignment at least Alignment,
otherwise false[.](#11.sentence-1)

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1036)

*Throws*: Nothing[.](#12.sentence-1)