Double List

doubleList.c

#include "doubleList.h"
/* linkedlist.c */
#include <stdlib.h>
#include "doubleList.h"

//static link head = NULL;
static List ListHead;

link make_node(unsigned char item)
{
    link p = malloc(sizeof *p);
    if (!p)
        exit(1);

    p->item = item;
    p->prev = p->next = NULL;
    return p;
}
void free_node(link p)
{
    free(p);
}

link search(unsigned char key)
{
    link p;
    //for (p = head; p; p = p->next)
    for (p = ListHead.head; p; p = p->next)
        if (p->item == key)
            return p;
    return NULL;
}

void insert(link p)
{
    //p->next = head;
    //p->next = ListHead.head;
    //ListHead.head = p;

    p->next = ListHead.head;
    if (ListHead.head)
        ListHead.head->prev = p;

    ListHead.head = p;
    p->prev = NULL;
}

link delete(link p)
{
//    link prev;
//    if (p == ListHead.head) {
//        ListHead.head = p->next;
//        return p;
//    }
//    for (prev = ListHead.head; prev; prev = prev->next)
//        if (prev->next == p) {
//            prev->next = p->next;
//            return p;
//        }
//    return NULL;

    if (p->prev)
        p->prev->next = p->next;
    else
        ListHead.head = p->next;

    if(p->next)
        p->next->prev = p->prev;

    return p;
}

link deleteUniformed(link p)
{
    link prev;
    if (p == ListHead.head) {
        ListHead.head = p->next;
        return p;
    }
    for (prev = ListHead.head; prev; prev = prev->next)
        if (prev->next == p) {
            prev->next = p->next;
            return p;
        }
    return NULL;
}

void traverse(void (*visit)(link))
{
    link p;
    for (p = ListHead.head; p; p = p->next)
        visit(p);
}
void destroy(void)
{
    link q, p = ListHead.head;
    ListHead.head = NULL;
    while (p) {
        q = p;
        p = p->next;
        free(q);
    }
}
void push(link p)
{
    insert(p);
}

link pop(void)
{
    if (ListHead.head == NULL)
        return NULL;
    else
        return delete(ListHead.head);
}

doubleList.h

#ifndef DOUBLE_LIST_DOUBLELIST_H
#define DOUBLE_LIST_DOUBLELIST_H

typedef struct node *link;
typedef struct list List;

struct node {
    unsigned char item;
    link prev, next;
};

struct list {
    link head;
    link tail;
};

link make_node(unsigned char item);
void free_node(link p);
link search(unsigned char key);
void insert(link p);
link delete(link p);
link deleteUniformed(link p);
void traverse(void (*visit)(link));
void destroy(void);
void push(link p);
link pop(void);

#endif //DOUBLE_LIST_DOUBLELIST_H

main.c

/* main.c */
#include <stdio.h>
#include "doubleList.h"
void print_item(link p)
{
    printf("%d\n", p->item);
}
int main(void)
{
    link p = make_node(10);
    insert(p);
    p = make_node(5);
    insert(p);
    p = make_node(90);
    insert(p);

    p = search(5);
    delete(p);
    free_node(p);

    p = search(90);
    deleteUniformed(p);
    free_node(p);

    traverse(print_item);

    destroy();

    p = make_node(100);
    push(p);
    p = make_node(200);
    push(p);
    p = make_node(250);
    push(p);
    while ((p = pop())) {
        print_item(p);
        free_node(p);
    }
    return 0;
}