std::is_null_pointer - cppreference.com (original) (raw)

| | | | | ---------------------------------------------- | | ------------- | | template< class T > struct is_null_pointer; | | (since C++11) |

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.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Possible implementation
  • 3.5 Notes
  • 3.6 Example
  • 3.7 Defect reports
  • 3.8 See also

[edit] Template parameters

[edit] 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

| | true if T is the type std::nullptr_t (possibly cv-qualified), false otherwise (public static member constant) | | ----------------------------------------------------------------------------------------------------------------------------------------------------------- |

Member functions

| | converts the object to bool, returns value (public member function) | | ---------------------------------------------------------------------- | | | returns value (public member function) |

Member types

[edit] Possible implementation

[edit] Notes

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

In libc++, std::is_null_pointer is not available in C++11 mode.

[edit] Example

#include   static_assert(std::is_null_pointer_v<decltype(nullptr)>); static_assert(!std::is_null_pointer_v<int*>); static_assert(<decltype(nullptr)>); static_assert(std::is_pointer_v<int*>);   int main() { }

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also