std::is_null_pointer

 

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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.

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, typename std::remove_cv<T>::type> {};

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

See also

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