关于使用 int 类型的 struct hack

Question

Can we do struct hack(using int type) as below

struct node{
   int i;
   struct node *next;
   int p[0];
}

int main(){
   struct node *n = // is this the correct hack i.e. p[10]?
      malloc(sizeof(struct node) + sizeof(int) * 10);
}

Also using int type with size 1

struct node{
   int i;
   struct node *next;
   int p[1];
}

int main(){
   struct node *n = // is this a correct hack i.e. p[10]?
      malloc(sizeof(struct node) + sizeof(int) * 10);
}

Answer 1

The former is the struct hack as used in c89. Validity of this construct has always been questionable.

The latter is a GNU struct hack, it makes use of a GNU extension and is not valid C.

The correct way to have a structures whose size could vary at run time is to use the c99 flexible array member feature.

struct node{
    int i;
    struct node *next;
    int p[];
}

int main(void)
{
     struct node *n = malloc(sizeof (struct node) + sizeof (int) * 10);
}

Answer 2

You used the same name twice. You will have to choose a different one. It is correct, apart from not using the correct syntax.

Should be [] not [1] or [0] , this way the code is not a "hack", but is legal from c99 onward, also called flexible array members.

struct node{
    int i;
    struct node *next;
    int n[];
} ;