std::alignment_of

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

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

Inherited from std::integral_constant

Member constants

value

[static]

alignof(T)
(public static member constant)

Member functions

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

`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 (C++11)(deprecated in C++23)	defines the type suitable for use as uninitialized storage for types of given size (class template)
aligned_union (C++11)(deprecated in C++23)	defines the type suitable for use as uninitialized storage for all given types (class template)
max_align_t (C++11)	trivial type with alignment requirement as great as any other scalar type (typedef)

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