Predefined null pointer constant (since C23) (original) (raw)

[edit] Syntax

| | | | | ----------- | | ----------- | | nullptr | | (since C23) | | | | |

[edit] Explanation

The keyword nullptr denotes a predefined null pointer constant. It is a non-lvalue of type nullptr_t. nullptr can be converted to a pointer types or bool, where the result is the null pointer value of that type or false respectively.

[edit] Keywords

nullptr

[edit] Example

Demonstrates that a copy of nullptr can also be used as a null pointer constant.

#include <stddef.h> #include <stdio.h> void g(int*) { puts("Function g called"); } #define DETECT_NULL_POINTER_CONSTANT(e)
_Generic(e,
void* : puts("void*"),
nullptr_t : puts("nullptr_t"),
default : puts("integer")
) int main() { g(nullptr); // OK g(NULL); // OK g(0); // OK auto cloned_nullptr = nullptr; g(cloned_nullptr); // OK [[maybe_unused]] auto cloned_NULL = NULL; // g(cloned_NULL); // implementation-defined: maybe OK [[maybe_unused]] auto cloned_zero = 0; // g(cloned_zero); // Error DETECT_NULL_POINTER_CONSTANT(((void*)0)); DETECT_NULL_POINTER_CONSTANT(0); DETECT_NULL_POINTER_CONSTANT(nullptr); DETECT_NULL_POINTER_CONSTANT(NULL); // implementation-defined }

Possible output:

Function g called Function g called Function g called Function g called void* integer nullptr_t void*

[edit] References