std::nullptr_t

From Cppreference

Defined in header `<cstddef>`

typedef decltype(nullptr) nullptr_t;		(C++11 feature)

std::nullptr_t is the type of the null pointer literal, nullptr.

[edit] Example

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

#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(NULL);  // ambiguous overload: all three functions are candidates
}

Output:

Pointer to integer overload
Pointer to double overload
null pointer overload

[edit] See also

nullptr

(keyword)

NULL

implementation-defined null pointer constant
(macro constant)