NAME¶

std::alignment_of - std::alignment_of

Synopsis¶

Defined in header <type_traits>
template< class T > (since C++11)
struct alignment_of;

Provides the member constant value equal to the alignment requirement of the type T,
as if obtained by an alignof expression. If T is an array type, returns the
alignment requirements of the element type. If T is a reference type, returns the
alignment requirements of the type referred to.

If alignof(T) is not a valid expression, the behavior is undefined.

The behavior of a program that adds specializations for alignment_of
or alignment_of_v
(since C++17) is undefined.

Helper variable template

template< class T > (since C++17)
inline constexpr std::size_t alignment_of_v = alignment_of<T>::value;

Inherited from std::integral_constant

Member constants¶

value alignof(T)
[static] (public static member constant)

Member functions¶

operator std::size_t converts the object to std::size_t, returns value
(public member function)
operator() returns value
(C++14) (public member function)

Member types¶

Type Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

Possible implementation¶

template< class T >
struct alignment_of : std::integral_constant<
std::size_t,
alignof(T)
> {};

Notes¶

This type trait predates the alignof keyword, which can be used to obtain the same
value with less verbosity.

Example¶

// Run this code

#include <cstdint>
#include <iostream>
#include <type_traits>

struct A {};
struct B {
std::int8_t p;
std::int16_t q;
};

int main()
{
std::cout << std::alignment_of<A>::value << ' ';
std::cout << std::alignment_of<B>::value << ' ';
std::cout << std::alignment_of<int>() << ' '; // alt syntax
std::cout << std::alignment_of_v<double> << '\n'; // c++17 alt syntax
}

Possible output:¶

1 2 4 8

See also¶

alignof operator(C++11) queries alignment requirements of a type
alignas specifier(C++11) specifies that the storage for the variable should be
aligned by specific amount
aligned_storage defines the type suitable for use as uninitialized
(C++11)(deprecated in C++23) storage for types of given size
(class template)
aligned_union defines the type suitable for use as uninitialized
(C++11)(deprecated in C++23) storage for all given types
(class template)
max_align_t trivial type with alignment requirement as great as any
(C++11) other scalar type
(typedef)