2024-09-29

`NULL` and `nullptr` in C++

As part of some other things, this question popped up and I had to look up the difference between NULL and nullptr in C++. Here’s what I found:

So nullptr is a keyword introduced in C++11 to represent a null pointer. It is of type std::nullptr_t.
NULL is a preprocessor macro that is defined as 0 or ((void*)0). It is not guaranteed that it will always expand to 0 (based on the code I found).

nullptr is more type-safe and causes fewer bugs than NULL because it is of type std::nullptr_t and can be used in place of any pointer type unlike NULL which can type casted to int too.

  /*===---- __stddef_null.h - Definition of NULL -----------------------------===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.
  * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  *
  *===-----------------------------------------------------------------------===
  */

  #if !defined(NULL) || !__building_module(_Builtin_stddef)

  /* linux/stddef.h will define NULL to 0. glibc (and other) headers then define
  * __need_NULL and rely on stddef.h to redefine NULL to the correct value again.
  * Modules don't support redefining macros like that, but support that pattern
  * in the non-modules case.
  */
  #undef NULL

  #ifdef __cplusplus
  #if !defined(__MINGW32__) && !defined(_MSC_VER)
  #define NULL __null
  #else
  #define NULL 0
  #endif
  #else
  #define NULL ((void*)0)
  #endif

  #endif

NULL and nullptr in C++

References

`NULL` and `nullptr` in C++