std::is_null_pointer - cppreference.com

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# std::is_null_pointer

From cppreference.com
< cpp‎ | types

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.

### [edit] Template parameters

T | - | a type to check

### [edit] Helper variable template

template< class T > constexpr bool is_null_pointer_v = is_null_pointer<T>::value; |  | (since C++17)

[edit]

## 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>

### [edit] Notes

std::is_pointer is false for std::nullptr_t because it is not a built-in pointer type.

### [edit] 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

### [edit] See also

is_void (C++11) | checks if a type is void (class template) [edit]
is_array (C++11) | checks if a type is an array type (class template) [edit]
is_pointer (C++11) | checks if a type is a pointer type (class template) [edit]
is_enum (C++11) | checks if a type is an enumeration type (class template) [edit]
is_union (C++11) | checks if a type is an union type (class template) [edit]
is_class (C++11) | checks if a type is a non-union class type (class template) [edit]
is_function (C++11) | checks if a type is a function type (class template) [edit]
is_object (C++11) | checks if a type is object type (class template) [edit]
std::experimental::is_null_pointer_v (library fundamentals TS) | variable template alias of `std::is_null_pointer::value` (variable template) [edit]

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