使用c语言实现双向链表

最近在学习C语言，在学习中，对很多知识又有了新的认识。

我是从java开始学习编程的，现在学了一遍C以后，更坚定了我对自身学习路线的认可。 C是你必须要学的一门编程语言，但绝不是第一门。

坚定我这个想法的原因有这么几个：

1. c语言过于底层，如果上手就以C为主语言开始学习，学习、理解成本相对大，这样效率就不会那么高。
2. C语言的统治领域与别的编程语言有非常大的区别。比如java擅长web，c++擅长客户端，而C适合系统。系统开发的工作岗位门槛较高，对语言底层理解和开发能力要求较高。而我自觉难达。
3. c语言过于底层，面向过程，手动内存，语法简单。开发过程像是一点一点的去扣去实现。真正适应了C 再去转向别的语言，会觉得处处受限。语言间的歧视链就是这样产生的。

我很庆幸我在已经学习了两三门高级语言后，再回过头学习C。或许我以后不会从事直接C开发的工作，但C对我编程的思想一定定有很大影响。

之前也听很多人说，写C就是从0做起，除了简单的函数库，什么都没了。数据结构需要全部自己实现。在学习java时，我曾阅读过大多数 数据结构 的源码，并付诸实现。两年之后，用c再来一遍，应该有不同的感受。

• 头文件：

#ifndef LINKED_LIST_H
#define LINKED_LIST_H#include <stddef.h>typedef int ll_data_t;
struct list;// constructs a new (empty) list
struct list *list_create(void);// counts the items on a list
size_t list_count(const struct list *list);// inserts item at back of a list
void list_push(struct list *list, ll_data_t item_data);// removes item from back of a list
ll_data_t list_pop(struct list *list);// inserts item at front of a list
void list_unshift(struct list *list, ll_data_t item_data);// removes item from front of a list
ll_data_t list_shift(struct list *list);// deletes a node that holds the matching data
void list_delete(struct list *list, ll_data_t data);// destroys an entire list
// list will be a dangling pointer after calling this method on it
void list_destroy(struct list *list);#endif

• 源文件

#include "linked_list.h"
#include <stdlib.h>struct list_node
{struct list_node *prev, *next;ll_data_t data;
};struct list
{struct list_node *first, *last;
};// constructs a new (empty) list
struct list *list_create(void)
{struct list *res = malloc(sizeof(struct list));res->first = NULL;res->last = NULL;return res;
}// counts the items on a list
size_t list_count(const struct list *list)
{if (!list)return 0;struct list_node *list_node = list->first;size_t res = 0;while (list_node){res++;list_node = list_node->next;}return res;
}// inserts item at back of a list
void list_push(struct list *list, ll_data_t item_data)
{if (!list){return;}struct list_node *node = malloc(sizeof(struct list_node));node->next = NULL;node->data = item_data;node->prev = list->last;if (!(list->first)){list->first = node;}else{list->last->next = node;}list->last = node;
}// removes item from back of a list
ll_data_t list_pop(struct list *list)
{struct list_node *prev = list->last->prev;ll_data_t res = list->last->data;if (!prev){list->first = NULL;}else{prev->next = NULL;}free(list->last);list->last = prev;return res;
}// inserts item at front of a list
void list_unshift(struct list *list, ll_data_t item_data)
{if(!list){ return;}struct list_node *new_node = malloc(sizeof(struct list_node));new_node->data = item_data;new_node->prev = NULL;new_node->next = (list->first) ? list->first : NULL;list->first = new_node;
}// removes item from front of a list
ll_data_t list_shift(struct list *list)
{if(!list || !list->first) { return 0;}struct list_node *first = list->first;ll_data_t val = first->data;if(!list->first->next) {// node was the only item in the list list->first = NULL;list->last= NULL;} else {list->first = first->next;list->first->prev = NULL;}free(first);return val;
}// deletes a node that holds the matching data
void list_delete(struct list *list, ll_data_t data)
{if (!list)return;struct list_node *next = list->first;while (next){if (next->data == data){if (!next->prev){list->first = next->next;}else{next->prev->next = next->next;}if (!next->next){list->last = next->prev;}else{next->next->prev = next->prev;}free(next);break;}next = next->next;}
}// destroys an entire list
// list will be a dangling pointer after calling this method on it
void list_destroy(struct list *list)
{if (!list){return;}struct list_node *node = list->first;while (node){struct list_node *tmp = node->next;free(node);node = tmp;}free(list);
}