std:: is_null_pointer
|
Defined in header
<type_traits>
|
||
|
template
<
class
T
>
struct is_null_pointer ; |
(since C++14) | |
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
>
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-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_is_null_pointer
|
201309L | (C++14) |
std::is_null_pointer
|
Example
#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
|
(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 a 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) |