std::nullptr_t (3) - Linux Manuals

std::nullptr_t: std::nullptr_t


std::nullptr_t - std::nullptr_t


Defined in header <cstddef>
typedef decltype(nullptr) nullptr_t; (since C++11)

std::nullptr_t is the type of the null pointer literal, nullptr. It is a distinct type that is not itself a pointer type or a pointer to member type.


If two or more overloads accept different pointer types, an overload for std::nullptr_t is necessary to accept a null pointer argument.
// Run this code

  #include <cstddef>
  #include <iostream>

  void f(int* pi)
     std::cout << "Pointer to integer overload\n";

  void f(double* pd)
     std::cout << "Pointer to double overload\n";

  void f(std::nullptr_t nullp)
     std::cout << "null pointer overload\n";

  int main()
      int* pi; double* pd;

      f(nullptr); // would be ambiguous without void f(nullptr_t)
      // f(0); // ambiguous call: all three functions are candidates
      // f(NULL); // ambiguous if NULL is an integral null pointer constant
                  // (as is the case in most implementations)


  Pointer to integer overload
  Pointer to double overload
  null pointer overload

See also

nullptr the pointer literal which specifies a null pointer value (C++11)
                implementation-defined null pointer constant
NULL (macro constant)

is_null_pointer checks if a type is std::nullptr_t
                (class template)