NAME¶

std::is_null_pointer - std::is_null_pointer

Synopsis¶

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

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

Inherited from std::integral_constant

Member constants¶

value true if T is the type std::nullptr_t (possibly cv-qualified) , false
[static] otherwise
(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_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.

Feature-test macro: __cpp_lib_is_null_pointer

Example¶

// Run this code

#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¶

is_void checks if a type is void
(C++11) (class template)
is_array checks if a type is an array type
(C++11) (class template)
is_pointer checks if a type is a pointer type
(C++11) (class template)
is_enum checks if a type is an enumeration type
(C++11) (class template)
is_union checks if a type is an union type
(C++11) (class template)
is_class checks if a type is a non-union class type
(C++11) (class template)
is_function checks if a type is a function type
(C++11) (class template)
is_object checks if a type is an object type
(C++11) (class template)