Void Pointer in Linked List

[sakura66]

Hi,I'm implementing a linked list with void * data.

typedef struct ListNode
{
  struct ListNode *prev;
  void *data;
  struct ListNode *next;
}ListNode;

I have a function void insert_at_index(void *data, int index)
Inside the function, I have something like..

newnode=(ListNode *)malloc(sizeof(ListNode));
newnode->data=data;

and the problem with this is that since data is a pointer, everytime I call the function, all nodes get the same value, that is the value entered last.
The nodes don't retain their original value!
Any help will be greatly appreciated!!!

[AbstractionAnon]

You're not showing enough code for a positive answer, but my guess is that you're passing a the same variable to your function each time, such as the following.

char what[20];
strcpy (what,"One");
insert_at_index (what, 0);
strcpy (what, "Two");
insert_at_index (what, 1);

The above code will store the same pointer (to what) each time. What node->data points to will contain whatever was last copied into what.

To do what you're trying to do, you're going to need to pass unique pointers when you call insert_at_index or make a copy of the data inside insert_at_index.

char * one = "One";
char * "two = "Two";
insert_at_index (one, 0);
insert_at_index (two, 1); 

BTW, using void pointers is a poor practice. You're giving up C++'s strong typing, and it makes it impossible to make a copy of the data inside your function. This is why the standard linked list container is a template.