前面我们介绍了如何在 C 语言中引入面向对象语言的一些特性来进行面向对象编程，从本篇开始，我们使用前面提到的技巧，陆续实现几个例子，最后呢，会提供一个基本的 http server 实现（使用 libevent ）。在这篇文章里，我们实现一个通用的数据结构：单链表。
这里实现的单链表，可以存储任意数据类型，支持增、删、改、查找、插入等基本操作。（本文提供的是完整代码，可能有些长。）
下面是头文件：
#ifndef SLIST_H
#define SLIST_H
#ifdef __cplusplus
extern "C" {
#endif
#define NODE_T(ptr, type) ((type*)ptr)
struct slist_node {
struct slist_node * next;
};
typedef void (*list_op_free_node)(struct slist_node *node);
/*
* return 0 on hit key, else return none zero
*/
typedef int (*list_op_key_hit_test)(struct slist_node *node, void *key);
struct single_list {
/* all the members must not be changed manually by callee */
struct slist_node * head;
struct slist_node * tail;
int size; /* length of the list, do not change it manually*/
/* free method to delete the node
*/
void (*free_node)(struct slist_node *node);
/*
* should be set by callee, used to locate node by key(*_by_key() method)
* return 0 on hit key, else return none zero
*/
int (*key_hit_test)(struct slist_node *node, void *key);
struct single_list *(*add)(struct single_list * list, struct slist_node * node);
struct single_list *(*insert)(struct single_list * list, int pos, struct slist_node *node);
/* NOTE: the original node at the pos will be freed by free_node */
struct single_list *(*replace)(struct single_list *list, int pos, struct slist_node *node);
struct slist_node *(*find_by_key)(struct single_list *, void * key);
struct slist_node *(*first)(struct single_list* list);
struct slist_node *(*last)(struct single_list* list);
struct slist_node *(*at)(struct single_list * list, int pos);
struct slist_node *(*take_at)(struct single_list * list, int pos);
struct slist_node *(*take_by_key)(struct single_list * list, void *key);
struct single_list *(*remove)(struct single_list * list, struct slist_node * node);
struct single_list *(*remove_at)(struct single_list *list, int pos);
struct single_list *(*remove_by_key)(struct single_list *list, void *key);
int (*length)(struct single_list * list);
void (*clear)(struct single_list * list);
void (*deletor)(struct single_list *list);
};
struct single_list * new_single_list(list_op_free_node op_free, list_op_key_hit_test op_cmp);
#ifdef __cplusplus
}
#endif
#endif // SLIST_H
struct single_list 这个类，遵循我们前面介绍的基本原则，不再一一细说。有几点需要提一下：
- 我们定义了 slist_node 作为链表节点的基类，用户自定义的节点，都必须从 slist_node 继承
- 为了支持节点（ node ）的释放，我们引入一个回调函数 list_op_free_node ，这个回调需要在创建链表时传入
- 为了支持查找，引入另外一个回调函数 list_op_key_hit_test
好了，下面看实现文件：
#include "slist.h"
#include <malloc.h>
static struct single_list * _add_node(struct single_list *list, struct slist_node *node)
{
if(list->tail)
{
list->tail->next = node;
node->next = 0;
list->tail = node;
list->size++;
}
else
{
list->head = node;
list->tail = node;
node->next = 0;
list->size = 1;
}
return list;
}
static struct single_list * _insert_node(struct single_list * list, int pos, struct slist_node *node)
{
if(pos < list->size)
{
int i = 0;
struct slist_node * p = list->head;
struct slist_node * prev = list->head;
for(; i < pos; i++)
{
prev = p;
p = p->next;
}
if(p == list->head)
{
/* insert at head */
node->next = list->head;
list->head = node;
}
else
{
prev->next = node;
node->next = p;
}
if(node->next == 0) list->tail = node;
list->size++;
}
else
{
list->add(list, node);
}
return list;
}
static struct single_list * _replace(struct single_list * list, int pos, struct slist_node *node)
{
if(pos < list->size)
{
int i = 0;
struct slist_node * p = list->head;
struct slist_node * prev = list->head;
for(; i < pos; i++)
{
prev = p;
p = p->next;
}
if(p == list->head)
{
/* replace at head */
node->next = list->head->next;
list->head = node;
}
else
{
prev->next = node;
node->next = p->next;
}
if(node->next == 0) list->tail = node;
if(list->free_node) list->free_node(p);
else free(p);
}
return list;
}
static struct slist_node * _find_by_key(struct single_list *list, void * key)
{
if(list->key_hit_test)
{
struct slist_node * p = list->head;
while(p)
{
if(list->key_hit_test(p, key) == 0) return p;
p = p->next;
}
}
return 0;
}
static struct slist_node *_first_of(struct single_list* list)
{
return list->head;
}
static struct slist_node *_last_of(struct single_list* list)
{
return list->tail;
}
static struct slist_node *_node_at(struct single_list * list, int pos)
{
if(pos < list->size)
{
int i = 0;
struct slist_node * p = list->head;
for(; i < pos; i++)
{
p = p->next;
}
return p;
}
return 0;
}
static struct slist_node * _take_at(struct single_list * list, int pos)
{
if(pos < list->size)
{
int i = 0;
struct slist_node * p = list->head;
struct slist_node * prev = p;
for(; i < pos ; i++)
{
prev = p;
p = p->next;
}
if(p == list->head)
{
list->head = p->next;
if(list->head == 0) list->tail = 0;
}
else if(p == list->tail)
{
list->tail = prev;
prev->next = 0;
}
else
{
prev->next = p->next;
}
list->size--;
p->next = 0;
return p;
}
return 0;
}
static struct slist_node * _take_by_key(struct single_list * list, void *key)
{
if(list->key_hit_test)
{
struct slist_node * p = list->head;
struct slist_node * prev = p;
while(p)
{
if(list->key_hit_test(p, key) == 0) break;
prev = p;
p = p->next;
}
if(p)
{
if(p == list->head)
{
list->head = p->next;
if(list->head == 0) list->tail = 0;
}
else if(p == list->tail)
{
list->tail = prev;
prev->next = 0;
}
else
{
prev->next = p->next;
}
list->size--;
p->next = 0;
return p;
}
}
return 0;
}
static struct single_list *_remove_node(struct single_list * list, struct slist_node * node)
{
struct slist_node * p = list->head;
struct slist_node * prev = p;
while(p)
{
if(p == node) break;
prev = p;
p = p->next;
}
if(p)
{
if(p == list->head)
{
list->head = list->head->next;
if(list->head == 0) list->tail = 0;
}
else if(p == list->tail)
{
prev->next = 0;
list->tail = prev;
}
else
{
prev->next = p->next;
}
if(list->free_node) list->free_node(p);
else free(p);
list->size--;
}
return list;
}
static struct single_list *_remove_at(struct single_list *list, int pos)
{
if(pos < list->size)
{
int i = 0;
struct slist_node * p = list->head;
struct slist_node * prev = p;
for(; i < pos ; i++)
{
prev = p;
p = p->next;
}
if(p == list->head)
{
list->head = p->next;
if(list->head == 0) list->tail = 0;
}
else if(p == list->tail)
{
list->tail = prev;
prev->next = 0;
}
else
{
prev->next = p->next;
}
if(list->free_node) list->free_node(p);
else free(p);
list->size--;
}
return list;
}
static struct single_list *_remove_by_key(struct single_list *list, void *key)
{
if(list->key_hit_test)
{
struct slist_node * p = list->head;
struct slist_node * prev = p;
while(p)
{
if(list->key_hit_test(p, key) == 0) break;
prev = p;
p = p->next;
}
if(p)
{
if(p == list->head)
{
list->head = list->head->next;
if(list->head == 0) list->tail = 0;
}
else if(p == list->tail)
{
prev->next = 0;
list->tail = prev;
}
else
{
prev->next = p->next;
}
if(list->free_node) list->free_node(p);
else free(p);
list->size--;
}
}
return list;
}
static int _length_of(struct single_list * list)
{
return list->size;
}
static void _clear_list(struct single_list * list)
{
struct slist_node * p = list->head;
struct slist_node * p2;
while(p)
{
p2 = p;
p = p->next;
if(list->free_node) list->free_node(p2);
else free(p2);
}
list->head = 0;
list->tail = 0;
list->size = 0;
}
static void _delete_single_list(struct single_list *list)
{
list->clear(list);
free(list);
}
struct single_list * new_single_list(list_op_free_node op_free, list_op_key_hit_test op_cmp)
{
struct single_list *list = (struct single_list *)malloc(sizeof(struct single_list));
list->head = 0;
list->tail = 0;
list->size = 0;
list->free_node = op_free;
list->key_hit_test = op_cmp;
list->add = _add_node;
list->insert = _insert_node;
list->replace = _replace;
list->find_by_key = _find_by_key;
list->first = _first_of;
list->last = _last_of;
list->at = _node_at;
list->take_at = _take_at;
list->take_by_key = _take_by_key;
list->remove = _remove_node;
list->remove_at = _remove_at;
list->remove_by_key = _remove_by_key;
list->length = _length_of;
list->clear = _clear_list;
list->deletor = _delete_single_list;
return list;
}
上面的代码就不一一细说了，下面是测试代码：
/* call 1 or N arguments function of struct */
#define ST_CALL(THIS,func,args...) ((THIS)->func(THIS,args))
/* call none-arguments function of struct */
#define ST_CALL_0(THIS,func) ((THIS)->func(THIS))
struct int_node {
struct slist_node node;
int id;
};
struct string_node {
struct slist_node node;
char name[16];
};
static int int_free_flag = 0;
static void _int_child_free(struct slist_node *node)
{
free(node);
if(!int_free_flag)
{
int_free_flag = 1;
printf("int node free\n");
}
}
static int _int_slist_hittest(struct slist_node * node, void *key)
{
struct int_node * inode = NODE_T(node, struct int_node);
int ikey = (int)key;
return (inode->id == ikey ? 0 : 1);
}
static int string_free_flag = 0;
static void _string_child_free(struct slist_node *node)
{
free(node);
if(!string_free_flag)
{
string_free_flag = 1;
printf("string node free\n");
}
}
static int _string_slist_hittest(struct slist_node * node, void *key)
{
struct string_node * sn = (struct string_node*)node;
return strcmp(sn->name, (char*)key);
}
void int_slist_test()
{
struct single_list * list = new_single_list(_int_child_free, _int_slist_hittest);
struct int_node * node = 0;
struct slist_node * bn = 0;
int i = 0;
printf("create list && nodes:\n");
for(; i < 100; i++)
{
node = (struct int_node*)malloc(sizeof(struct int_node));
node->id = i;
if(i%10)
{
list->add(list, node);
}
else
{
list->insert(list, 1, node);
}
}
printf("create 100 nodes end\n----\n");
printf("first is : %d, last is: %d\n----\n",
NODE_T( ST_CALL_0(list, first), struct int_node )->id,
NODE_T( ST_CALL_0(list, last ), struct int_node )->id);
assert(list->size == 100);
printf("list traverse:\n");
for(i = 0; i < 100; i++)
{
if(i%10 == 0) printf("\n");
bn = list->at(list, i);
node = NODE_T(bn, struct int_node);
printf(" %d", node->id);
}
printf("\n-----\n");
printf("find by key test, key=42:\n");
bn = list->find_by_key(list, (void*)42);
assert(bn != 0);
node = NODE_T(bn, struct int_node);
printf("find node(key=42), %d\n------\n", node->id);
printf("remove node test, remove the 10th node:\n");
bn = list->at(list, 10);
node = NODE_T(bn, struct int_node);
printf(" node 10 is: %d\n", node->id);
printf(" now remove node 10\n");
list->remove_at(list, 10);
printf(" node 10 was removed, check node 10 again:\n");
bn = list->at(list, 10);
node = NODE_T(bn, struct int_node);
printf(" now node 10 is: %d\n------\n", node->id);
printf("replace test, replace node 12 with id 1200:\n");
bn = list->at(list, 12);
node = NODE_T(bn, struct int_node);
printf(" now node 12 is : %d\n", node->id);
node = (struct int_node*)malloc(sizeof(struct int_node));
node->id = 1200;
list->replace(list, 12, node);
bn = list->at(list, 12);
node = NODE_T(bn, struct int_node);
printf(" replaced, now node 12 is : %d\n----\n", node->id);
printf("test remove:\n");
ST_CALL(list, remove, bn);
bn = ST_CALL(list, find_by_key, (void*)1200);
assert(bn == 0);
printf("test remove ok\n----\n");
printf("test remove_by_key(90):\n");
ST_CALL(list, remove_by_key, (void*)90);
bn = ST_CALL(list, find_by_key, (void*)90);
assert(bn == 0);
printf("test remove_by_key(90) end\n----\n");
printf("test take_at(80):\n");
bn = ST_CALL(list, take_at, 80);
printf(" node 80 is: %d\n", NODE_T(bn, struct int_node)->id);
free(bn);
printf("test take_at(80) end\n");
int_free_flag = 0;
printf("delete list && nodes:\n");
list->deletor(list);
printf("delete list && nodes end\n");
printf("\n test add/insert/remove/delete/find_by_key/replace...\n");
}
void string_slist_test()
{
struct single_list * list = new_single_list(_string_child_free, _string_slist_hittest);
}
void slist_test()
{
int_slist_test();
string_slist_test();
}
测试代码里主要演示了：
- 自定义链表节点类型
- 定义释放回调
- 定义用于查找的 hit test 回调
- 如何创建链表
- 如何使用（ add 、remove 、 take 、find 、 insert 等）
相信到这里，单链表的使用已经不成问题了。
以单链表为基础，可以进一步实现很多数据结构，比如树（兄弟孩子表示法），比如 key-value 链表等等。接下来根据例子的需要，会择机进行展示。