# std::alignment_of

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< cpp‎ | types

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 > 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 <iostream>
    #include <type_traits>

    class A {};

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

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)

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