C++

Reference

<type_traits>

class template
<type_traits>

std::is_null_pointer

template <class T> struct is_null_pointer;
Is null pointer

Trait class that identifies whether the type of T is nullptr_t.

Note that this trait only classifies the type of T, not whether the potential value of a pointer is a null pointer value.

It inherits from integral_constant as being either true_type or false_type.

Template parameters

T
A type.

Member types

Inherited from integral_constant:
member typedefinition
value_typebool
typeeither true_type or false_type

Member constants

Inherited from integral_constant:
member constantdefinition
valueeither true or false

Member functions

Inherited from integral_constant:
operator bool
Returns value (public member function)

Example

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// is_null_pointer example
#include <iostream>
#include <type_traits>

int main() {
  int* a = 0;
  std::cout << std::boolalpha;
  std::cout << "is_null_pointer:\n";
  std::cout << "decltype(a): " << std::is_null_pointer<decltype(a)>::value << '\n';
  std::cout << "decltype(nullptr): " << std::is_null_pointer<decltype(nullptr)>::value << '\n';
  return 0;
}

Output:
is_pointer:
decltype(a): false
decltype(nullptr): true


See also

is_lvalue_reference
Is lvalue reference (class template)
is_rvalue_reference
Is rvalue reference (class template)
is_member_object_pointer
Is member object pointer (class template)
is_member_function_pointer
Is member function pointer (class template)
is_member_pointer
Is member pointer type (class template)
is_function
Is function (class template)