Linked list with dynamically variable number of members within each node

If you've a finite set of possible node type, then you may define a struct for each node type, and store, in every node both

<ul><li>a pointer of the actual data structure, as <code>void *</code>.</li>
<li>a integer value representing the actual type of the data.</li>

(of course you've also to store a pointer to the next item of the list...)

for instance:

/* data structs, i.e. node types */
typedef struct tagPoint
{
  int x;
  int y;
}Point;

typedef struct tagUser
{
  const char * name;
  int age;
  /*..*/
} User;
/*... other data types...*/

typedef enum  TagNodeType
{
  ePoint,
  eUser,
  /*...*/
  eNODETYPES
} NodeType;

typedef struct TagListItem
{
  NodeType nt;
  void * pData;
  struct TagListItem * pNext;
} ListItem;

Then implement a addListItem function accepting a pointer to actual data and a value representing the data type.
On retrieving data you've to check the nt field in order to properly cast the pData pointer.

:)