std::is_null_pointer (3) - Linux Manuals

std::is_null_pointer: std::is_null_pointer

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.

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 otherwise
         (public static member constant)
[static]

Member functions

              converts the object to bool, returns value
operator bool (public member function)

operator() returns value
              (public member function)
(C++14)

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

// 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