| 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 > 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> |
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 object type (class template) |
| std::experimental::is_null_pointer_v
(library fundamentals TS) | variable template alias of std::is_null_pointer::value (variable template) |
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