std::nullptr_t (3) - Linux Manuals

std::nullptr_t: std::nullptr_t

NAME

std::nullptr_t - std::nullptr_t

Synopsis

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.

Example

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(pi);
      f(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)
  }

Output:

  Pointer to integer overload
  Pointer to double overload
  null pointer overload