std::is_null_pointer
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
.
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 > 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, 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 testing macro: __cpp_lib_is_null_pointer
.
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 an object type (class template) |
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