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* 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) |
#include <stdlib.h>
#include <stdio.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;
// many pointer-returning functions use null pointers to indicate error
char *ptr = malloc(10);
if (ptr == NULL) printf("Out of memory");
free(ptr);
}
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