🚋 Doubly linked list example using 4.4BSD queue.h preprocessor macros..

linked-lists.c

/*
 * An implementation of doubly linked lists in ANSI C using sys/queue.h
 *
 * gcc -Wall -ansi -pedantic -O2 -o linked-lists linked-lists.c
 *
 * Written By:    Derek Callaway [decal (AT) sdf {D0T} org]
 * Last Modified: Fri Dec 29 09:22:40 UTC 2017
 *
 */

#include<stdio.h>
#include<stdlib.h>
#include<sys/queue.h>

static void vexit(const char *funcname) {
  perror(funcname);

  exit(EXIT_FAILURE);
}

signed int main(int argc, char *argv[], char *envp[]) {
  LIST_HEAD(listhead, entry) head;
  
  struct entry {
    int x;
    LIST_ENTRY(entry) entries; /* List. */
  } *n1, *n2, *np;
  
  LIST_INIT(&head); /* Initialize the list. */

  n1 = malloc(sizeof *n1); /* Insert at the head. */
  
  if(!n1)
    vexit("malloc");

  n1->x = 1;

  LIST_INSERT_HEAD(&head, n1, entries);

  n2 = malloc(sizeof *n2); /* Insert after. */
  
  if(!n2)
    vexit("malloc");

  n2->x = 2;

  LIST_INSERT_AFTER(n1, n2, entries);

  /* Forward traversal. */
  for (np = head.lh_first; np; np = np->entries.le_next)
    printf("%d\n", np->x);

  for(np = head.lh_first; np; np = np->entries.le_next)
    LIST_REMOVE(np, entries); /* Delete. */
  
  exit(EXIT_SUCCESS);
}