Defined in header <stddef.h> | ||
|---|---|---|
Defined in header <string.h> | ||
Defined in header <wchar.h> | ||
Defined in header <time.h> | ||
Defined in header <locale.h> | ||
Defined in header <stdio.h> | ||
Defined in header <stdlib.h> | ||
#define NULL /*implementation-defined*/ |
The macro NULL is an implementation-defined null pointer constant, which may be.
0 void*
| (since C23) |
A null pointer constant may be converted to any pointer type; such conversion results in the null pointer value of that type.
// 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 <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
int main(void)
{
// any kind of pointer can be set to NULL
int* 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 error
char *ptr = malloc(0xFULL);
if (ptr == NULL)
printf("Out of memory");
else
printf("ptr = %#" PRIxPTR"\n", (uintptr_t)ptr);
free(ptr);
}Possible output:
(nil) (nil) (nil) ptr = 0xc001cafe
|
(C23) | the type of the predefined null pointer constant nullptr (typedef) |
C++ documentation for NULL |
|
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