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.

#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
(macro constant)
checks if a type is std::nullptr_t
(class template)

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