std::alignment_of

template< class T >
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 >
inline constexpr std::size_t alignment_of_v = alignment_of<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

#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
}

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See also