2019/9/3 null pointer and the pointer field

void * pointer, the type of null pointer, the pointer can point to any type of

int a =10;

void *pa = &a;

int b = (* (int *) pa); // correct int b = (int *) (* pa) is wrong

 

Field guide: pointing to illegal memory pointer or have been destroyed

Hazard: The cause unpredictable damage to the operating system

The reason:

1, the pointer does not point definition, i.e., not initialized

Solution: Either point to legitimate space, either point to NULL (#define NULL ((void *) 0))

char *p = NULL;

char *p = (char *)malloc(100);

 

2, then the pointer is free or delete, the pointer is just freed memory, the pointer value is not changed. At this point p reduced to a "field guide", p point does not make sense

Solve: free (p);

p = NULL; (blank)