std::is_unbounded_array - cppreference.com

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template< class T > struct is_unbounded_array;		(since C++20)

std::is_unbounded_array is a UnaryTypeTrait.

Checks whether T is an arrays of unknown bound. Provides the member constant value which is equal to true, if T is an array type of unknown bound. Otherwise, value is equal to false.

If the program adds specializations for std::is_unbounded_array or std::is_unbounded_array_v, the behavior is undefined.

Template parameters

Helper variable template

template< class T > constexpr bool is_unbounded_array_v = is_unbounded_array<T>::value;		(since C++20)

Inherited from std::integral_constant

Member constants

true if T is an array type of unknown bound., false otherwise
(public static member constant)

Member functions

	converts the object to `bool`, returns `value` (public member function)
	returns `value` (public member function)

Member types

Type	Definition
`value_type`	`bool`
`type`	`std::integral_constant<bool, value>`

Possible implementation

template<class T>
struct is_unbounded_array: std::false_type {};

template<class T>
struct is_unbounded_array<T[]> : std::true_type {};

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_bounded_array_traits`	`201902L`	(C++20)	std::is_bounded_array, `std::is_unbounded_array`

Example

#include <type_traits>

class A {};

static_assert
(""
    && std::is_unbounded_array_v<A> == false
    && std::is_unbounded_array_v<A[]> == true
    && std::is_unbounded_array_v<A[3]> == false
    && std::is_unbounded_array_v<float> == false
    && std::is_unbounded_array_v<int> == false
    && std::is_unbounded_array_v<int[]> == true
    && std::is_unbounded_array_v<int[3]> == false
);

int main() {}

	checks if a type is an array type (class template) [edit]
	checks if a type is an array type of known bound (class template) [edit]
	obtains the size of an array type along a specified dimension (class template) [edit]