NAME¶

std::is_unbounded_array - std::is_unbounded_array

Synopsis¶

Defined in header <type_traits>
template< class T > (since C++20)
struct is_unbounded_array;

Checks whether T is an array type 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.

The behavior of a program that adds specializations for is_unbounded_array or
is_unbounded_array_v is undefined.

Template parameters¶

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants¶

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

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (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: __cpp_lib_bounded_array_traits

Example¶

// Run this code

#include <iostream>
#include <type_traits>

#define OUT(...) std::cout << #__VA_ARGS__ << " : " << __VA_ARGS__ << '\n'

class A {};

int main()
{
std::cout << std::boolalpha;
OUT( std::is_unbounded_array_v<A> );
OUT( std::is_unbounded_array_v<A[]> );
OUT( std::is_unbounded_array_v<A[3]> );
OUT( std::is_unbounded_array_v<float> );
OUT( std::is_unbounded_array_v<int> );
OUT( std::is_unbounded_array_v<int[]> );
OUT( std::is_unbounded_array_v<int[3]> );
}

Output:¶

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

See also¶

is_array checks if a type is an array type
(C++11) (class template)
is_bounded_array checks if a type is an array type of known bound
(C++20) (class template)
extent obtains the size of an array type along a specified dimension
(C++11) (class template)