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About: About this document Generalised List Data Type

In many C programs you will see various implementations and re-implementations of lists and stacks, each tied to its own particular project. It is surprisingly simple to write a catch-all implementation, as I have done here with a generalised list operation API in `list.h':

#ifndef SIC_LIST_H
#define SIC_LIST_H 1

#include <sic/common.h>


typedef struct list {
  struct list *next;    /* chain forward pointer*/
  void *userdata;       /* incase you want to use raw Lists */
} List;

extern List *list_new       (void *userdata);
extern List *list_cons      (List *head, List *tail);
extern List *list_tail      (List *head);
extern size_t list_length   (List *head);


#endif /* !SIC_LIST_H */

The trick is to ensure that any structures you want to chain together have their forward pointer in the first field. Having done that, the generic functions declared above can be used to manipulate any such chain by casting it to List * and back again as necessary.

For example:

struct foo {
  struct foo *next;

  char *bar;
  struct baz *qux;

  struct foo *foo_list = NULL;

  foo_list = (struct foo *) list_cons ((List *) new_foo (),
                                       (List *) foo_list);

The implementation of the list manipulation functions is in `list.c':

#include "list.h"

List *
list_new (void *userdata)
  List *new = XMALLOC (List, 1);

  new->next = NULL;
  new->userdata = userdata;

  return new;

List *
list_cons (List *head, List *tail)
  head->next = tail;
  return head;

List *
list_tail (List *head)
  return head->next;

list_length (List *head)
  size_t n;
  for (n = 0; head; ++n)
    head = head->next;

  return n;

This document was generated by Gary V. Vaughan on February, 8 2006 using texi2html