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8.3 nullptr

Gnulib module: nullptr

The nullptr module arranges for nullptr to act like standard C and C++.

The nullptr keyword yields a null pointer. It differs from the NULL macro, in that NULL might be an integer whereas nullptr is of a special nullptr_t type with only one value, namely nullptr itself. Using nullptr can help some compilers emit more sensible warnings, can avoid the need to cast a null pointer passed to a function prototyped with an ellipsis, and removes the need to include <stddef.h> merely to define NULL.

Portability problems fixed by Gnulib:

• Some platforms lack nullptr: For C: GCC 12, Clang 15, and other pre-2023 C compilers. For C++: pre-2011 C++ compilers.
• Some platforms incorrectly warn when nullptr is a sentinel argument: GCC 13.2 and 14.0.

Portability problems not fixed by Gnulib:

• On older platforms, nullptr is a macro instead of a keyword.
• On older platforms, nullptr does not have the type nullptr_t. In C, it has type void *; in C++ it has an integer type.
• On older platforms Gnulib cannot easily emulate nullptr_t, so null pointer type checking is more error prone. In C, _Generic expressions cannot reliably distinguish the type of nullptr from integer or void * types. C++ overloading has similar limitations.