std::is_null_pointer

< cpp‎ | types
Defined in header <type_traits>
template< class T >
struct is_null_pointer;
 (since C++14)

Checks whether T is the type std::nullptr_t.

Provides the member constant value that is equal to true, if T is the type std::nullptr_t, const std::nullptr_t, volatile std::nullptr_t, or const volatile std::nullptr_t.

Otherwise, value is equal to false.

The behavior of a program that adds specializations for is_null_pointer or is_null_pointer_v (since C++17) is undefined.

Template parameters

T - a type to check

Helper variable template

template< class T >
inline constexpr bool is_null_pointer_v = is_null_pointer<T>::value;
 (since C++17)

Inherited from std::integral_constant

Member constants

value
[static]
 true if T is the type std::nullptr_t (possibly cv-qualified) , 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_null_pointer : std::is_same<std::nullptr_t, std::remove_cv_t<T>> {};

Notes

std::is_pointer is false for std::nullptr_t because it is not a built-in pointer type.

Example

#include <iostream>
#include <type_traits>
 
int main()
{
    std::cout << std::boolalpha
              << std::is_null_pointer< decltype(nullptr) >::value << ' '
              << std::is_null_pointer< int* >::value << '\n'
              << std::is_pointer< decltype(nullptr) >::value << ' '
              << std::is_pointer<int*>::value << '\n';
}

Output:

true false
false true

See also

(C++11)
 checks if a type is void
(class template)
(C++11)
 checks if a type is an array type
(class template)
(C++11)
 checks if a type is a pointer type
(class template)
(C++11)
 checks if a type is an enumeration type
(class template)
(C++11)
 checks if a type is an union type
(class template)
(C++11)
 checks if a type is a non-union class type
(class template)
(C++11)
 checks if a type is a function type
(class template)
(C++11)
 checks if a type is an object type
(class template)