std::is_unbounded_array

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

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.

Template parameters

a type to check

Helper variable template

template< class T >
inline constexpr bool is_unbounded_array_v = is_unbounded_array<T>::value;

(since C++20)

Inherited from std::integral_constant

Member constants

value

[static]

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

Member functions

operator bool	converts the object to `bool`, returns `value` (public member function)
operator() (C++14)	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 {};

Example

#include <iostream>
#include <type_traits>
 
class A {};
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_unbounded_array_v<A> << '\n';
    std::cout << std::is_unbounded_array_v<A[]> << '\n';
    std::cout << std::is_unbounded_array_v<A[3]> << '\n';
    std::cout << std::is_unbounded_array_v<float> << '\n';
    std::cout << std::is_unbounded_array_v<int> << '\n';
    std::cout << std::is_unbounded_array_v<int[]> << '\n';
    std::cout << std::is_unbounded_array_v<int[3]> << '\n';
}

Output:

false
true
false
false
false
true
false

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