std::alignment_of

 

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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.

Helper variable template

template< class T > 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 <iostream>
#include <type_traits>
 
class A {};
 
int main() 
{
    std::cout << std::alignment_of<A>::value << '\n';
    std::cout << std::alignment_of<int>::value << '\n';
    std::cout << std::alignment_of<double>::value << '\n';
}

Output:

1
4
8

See also

alignof operator	queries alignment requirements of a type (since C++11)
aligned_storage (C++11)	defines the type suitable for use as uninitialized storage for types of given size (class template)
aligned_union (C++11)	defines the type suitable for use as uninitialized storage for all given types (class template)
max_align_t (C++11)	POD type with alignment requirement as great as any other scalar type (typedef)
std::experimental::alignment_of_v (library fundamentals TS)	variable template alias of std::alignment_of::value (variable template)