NULL

From cppreference.com

Defined in header `<cstddef>`
Defined in header `<cstring>`
Defined in header `<cwchar>`
Defined in header `<ctime>`
Defined in header `<clocale>`
Defined in header `<cstdio>`

#define NULL /implementation-defined/

Defines the null pointer constant, which is an integral constant expression prvalue of integer type that evaluates to zero or a prvalue of type std::nullptr_t. The null pointer constant may be implicitly converted to any pointer type; such conversion results in the null pointer value of that type. If the null pointer constant has integer type, it may be converted to a prvalue of type std::nullptr_t.

[edit] Possible implementation

#define NULL 0
//since C++11
#define NULL nullptr

[edit] Example

run this code

#include <cstddef>
class S;
int main()
{
    int* p = NULL;
    int* p2 = static_cast<std::nullptr_t>(NULL);
    void(*f)(int) = NULL;
    int S::*mp = NULL;
    void(S::*mfp)(int) = NULL;
}

[edit] See also


nullptr	the pointer literal which specifies a null pointer value (C++11)

nullptr_t (C++11)	the type of the null pointer literal `nullptr` (typedef)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)