How to reference values of structure from variable of a different structure?

Question

Sorry if the title is a little confusing, as a beginner to C I really didn't know how else to put it. So I'm trying to create a singly linkedlist where each node not only has a pointer to the next node, but also a pointer to sub-linkedlist that starts from that node. Basically each node has its own linkedlist. In trying to create this LL, I've got a struct that houses characteristics of what each node should have, such as a pointer to the next node and a pointer to the linkedlist of data that stems from it. I've heard that you're actually able to make a struct of a struct. I want to make a second struct that structures the types of data that the node is holding:

struct NODE{
    void* data;
    struct Node* next;
}NODE;

typedef struct stuff{
    int data1;
    int data2;
    int data3;
}STUFF;

My question now, is that say I have a node from struct NODE like "NODE* node", how would I reference this node's types of data (data1, data2, etc)? I've tried casting, but not sure if I'm doing it wrong but something like this:

(STUFF)node->data1= DATA1; 
//where DATA1 is of course already defined to be some int

I did this inside of a function, and I get the error "Assignment to cast is illegal, lvalue casts are not supported".

It's not clear what you mean by this "sub-linked-list". You seem to be describing something of type struct stuff, except that does not look like a list node. Are you trying to pack this structure inside a void*? Please construct an example list and its contents to illustrate what you're trying to do. It sounds like you want a linked list where the data member of each node points to another struct NODE (as the sub-list) and each of those nodes have their data member point to a struct stuff value. Is that correct? — paddy
– paddy, Commented Nov 29, 2021 at 3:24
what is the difference between NODE and Node types? Where is Node defined? — vmp
– vmp, Commented Nov 29, 2021 at 3:26
Basically I wanted to create a singly linkedlist where, compared to a basic LL each node only has just 1 piece of data, this LL has nodes that have multiple pieces of data (data1, data2, etc.) — Ides784
– Ides784, Commented Nov 29, 2021 at 3:28
then why dont you use a pointer of type STUFF instead of void? — vmp
– vmp, Commented Nov 29, 2021 at 3:28

vmp · Accepted Answer · 2021-11-29 03:36:50Z

1

Concerning your cast problem... Here is how you could do it.

typedef struct Node{
    void* data;
    struct Node* next;
}NODE;

typedef struct stuff{
    int data1;
    int data2;
    int data3;
}STUFF;

int main()
{
    NODE *n = malloc(sizeof(NODE));
    n->data = malloc(sizeof(STUFF));
    STUFF *s = n->data;
    s->data1 = 15;
    printf("%d", ((STUFF*) n->data)->data1);
    return 0;
}

answered Nov 29, 2021 at 3:36

vmp

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