取消引用“ void *”指针—列表中的列表

Question

I want to write a program with lists in lists. So there is the list.h file :

typedef struct node {
    void *ptr;
    struct node *next;
    struct node *prev;
} NODE;

typedef struct list {
    struct node *head;
    struct node *tail;
    int size;
    char name[MAX_SIZE_NAME];
} LIST;

At first I have the list, for example list_. Now i allocate 5 elements.

And in every node I want to allocate a new list. I tryed with this code :

if (list_->head->next == list_->tail) {
    list_ins_next(list_);
    ptr = list_->tail->prev;
    ptr->ptr = malloc(sizeof(LIST));
    ptr->ptr->head = malloc(sizeof(NODE));

Sorry I dont have so much programming experience, but it would be great if you would help me

the error is : dereferencing 'void *' pointer

Answer 1

ptr->ptr->head = malloc(sizeof(NODE));

is equivalent to:

(*(ptr->ptr)).head = malloc(sizeof(NODE));

The expression *(ptr->ptr) is not valid since you can't dereference a void* .

You need a pointer of type LIST* to dereference it and then use the head member of the object.

Use:

((LIST*)ptr->ptr)->head = malloc(sizeof(NODE));