Question

I am writing a program that implements a stack in c. I want each node to take any type of data(ie int char struct etc) if I declare my node struct as

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

Does that allow my void pointer data to point to any type of memory?

Answer 1

Yes, but there are some caveats involving dereferencing your void pointer to access the data inside.

Basically, say you have a node:

Node *node;

And you have some Point structure:

typedef struct Point {
    int x;
    int y;
} Point;

And you put a point in a node:

Point *p = malloc(sizeof(Point));
p->x = 0;
p->y = 3;
node->data = p;

In order to access the members of the point, you have to use a typecast:

printf("%d\n", ((Point *)node->data)->x);

Or you can assign a pointer of the correct type and copy the void pointer:

Point *p = node->data;
printf("%d\n", p->x);

Because this won’t work:

printf("%d\n", node->data->x);

That’s because a void pointer contains no type information for the compiler to make sense of what’s being pointed to by a void pointer.

And that’s pretty much all you need to know about how to use void pointers.