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;

std::is_null_pointer is a UnaryTypeTrait.

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.

If the program adds specializations for std::is_null_pointer
or std::is_null_pointer_v
(since C++17), the behavior 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 Value Std Feature
__cpp_lib_is_null_pointer 201309L (C++14) std::is_null_pointer

Example¶

// Run this code

#include <type_traits>

static_assert(std::is_null_pointer_v<decltype(nullptr)>);
static_assert(!std::is_null_pointer_v<int*>);
static_assert(!std::is_pointer_v<decltype(nullptr)>);
static_assert(std::is_pointer_v<int*>);

int main()
{
}

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 a 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)