Predefined null pointer constant (since C23)
From cppreference.com
Syntax
nullptr
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(since C23) | ||||||||
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.
Keywords
Example
Demonstrates that a copy of nullptr can also be used as a null pointer constant.
Run this code
#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*
References
- C23 standard (ISO/IEC 9899:2024):
- 6.4.4.6 Predefined constants (p: 66)
See also
| implementation-defined null pointer constant (macro constant) | |
| (C23) |
the type of the predefined null pointer constant nullptr (typedef) |
| C++ documentation for nullptr
| |