Defined in header <locale.h> | ||
Defined in header <stddef.h> | ||
Defined in header <stdio.h> | ||
Defined in header <stdlib.h> | ||
Defined in header <string.h> | ||
Defined in header <time.h> | ||
Defined in header <wchar.h> | ||
#define NULL /*implementation-defined*/ | ||
The macroNULL is an implementation-defined null pointer constant, which may be
| (since C23) |
A null pointer constant may beconverted to any pointer type; such conversion results in the null pointer value of that type.
Contents |
POSIX requiresNULL to be defined as an integer constant expression with the value0 cast tovoid*.
// C++ compatible:#define NULL 0// C++ incompatible:#define NULL (10*2 - 20)#define NULL ((void*)0)// since C23 (compatible with C++11 and later)#define NULL nullptr |
#include <inttypes.h>#include <stdint.h>#include <stdio.h>#include <stdlib.h> int main(void){// any kind of pointer can be set to NULLint* p= NULL;struct S*s= NULL;void(*f)(int,double)= NULL;printf("%p %p %p\n",(void*)p,(void*)s,(void*)(long)f); // many pointer-returning functions use null pointers to indicate errorchar*ptr=malloc(0xFULL);if(ptr== NULL)printf("Out of memory");elseprintf("ptr = %#"PRIxPTR"\n",(uintptr_t)ptr);free(ptr);}
Possible output:
(nil) (nil) (nil)ptr = 0xc001cafe
(C23) | the type of the predefined null pointer constantnullptr (typedef)[edit] |
C++ documentation forNULL | |
