前言: 在企业中发开C,在没有前人积累的情况下实在是一件困难的事情,尤其是设计到纯C语言系统架构,内存设计,业务与数据结构的完全解耦和,有时候确实很让人苦恼的事情,C中没有C++中的template ,没有C++ 中丰富的异常处理,没有JAVA中线程安全直接就可以使用的容器,但是生活还是要继续的。。。。。现在就来讨论一下在企业中如何快速开发一款可以使用的双向循环链表。
一:双向循环链表(C语言版本)的巅峰应用
参考自:http://blog.youkuaiyun.com/coding__madman/article/details/51325646
可以做些什么呢?我觉得可以将其复用到用户态编程中,以后在用户态下编程就不需要写一些关于链表的代码了,直接将内核中list.h中的代码拷贝过来用。也可以整理出my_list.h,在以后的用户态编程中直接将其包含到C文件中
1. 链表对比
传统链表和内核链表
传统链表:一般指的是单向链表
struct List
{
struct list *next;//链表结点指针域
};
内核链表:双向循环链表 设计初衷是设计出一个通用统一的双向链表!
struct list_head
{
struct list_head *head, *prev;
};
list_head结构包含两个指向list_head结构体的指针
prev和next,由此可见,内核的链表具备双链表功能,实际上,通常它都组织成双向循环链表
2. 内核链表使用
1. INIT_LIST_HEAD:创建链表
2. list_add:在链表头插入节点
3. list_add_tail:在链表尾插入节点
4. list_del:删除节点
5. list_entry:取出节点
6. list_for_each:遍历链表
我们可以发现,在linux内核中链表的使用实现了解耦和,也就是传说中的业务与数据结构相分离,一点我在http://blog.youkuaiyun.com/qq_32378713/article/details/79328831 这篇博客中就有详细的分析,但是那一天我自己实现了一个简单的单链表,现在要用这个思想实现一个双向循环链表,也就是linux内核中的链表模式(其实所谓的线程安全在学习了linux系统编程之后我们就可以清楚的了解到它的重要性,以及怎么实现,无非就两种做法,一种是在链表进行操作的时候进行加锁,另外一种就是原子操作 atomic,现在我们只讨论业务与数据结构的分离不考虑多线程情况)
二: 我的双向循环链表的实现,以及简单业务模型的测试
(时间有限,简单的做了一个循环单链表,双向链表也只是在创建、插入、删除中有略微的不同,大致是一样的)
circleList .h
#ifndef _CIRCLELIST_H_
#define _CIRCLELIST_H_
typedef void CircleList;
/*
typedef struct _tag_CircleListNode CircleListNode;
struct _tag_CircleListNode
{
CircleListNode* next;
};
*/
typedef struct _tag_CircleListNode
{
struct _tag_CircleListNode * next;
}CircleListNode;
CircleList* CircleList_Create();
void List_Destroy(CircleList* list);
void CircleList_Clear(CircleList* list);
int CircleList_Length(CircleList* list);
int CircleList_Insert(CircleList* list, CircleListNode* node, int pos);
CircleListNode* CircleList_Get(CircleList* list, int pos);
CircleListNode* CircleList_Delete(CircleList* list, int pos);
//add
CircleListNode* CircleList_DeleteNode(CircleList* list, CircleListNode* node);
CircleListNode* CircleList_Reset(CircleList* list);
CircleListNode* CircleList_Current(CircleList* list);
CircleListNode* CircleList_Next(CircleList* list);
#endif
circleList.cpp
#include <stdio.h>
#include <malloc.h>
#include "CircleList.h"
typedef struct _tag_CircleList
{
CircleListNode header;
CircleListNode* slider;
int length;
} TCircleList;
CircleList* CircleList_Create() // O(1)
{
TCircleList* ret = (TCircleList*)malloc(sizeof(TCircleList));
if (ret == NULL)
{
return NULL;
}
ret->length = 0;
ret->header.next = NULL;
ret->slider = NULL;
return ret;
}
void CircleList_Destroy(CircleList* list) // O(1)
{
if (list == NULL)
{
return ;
}
free(list);
}
void CircleList_Clear(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
if (sList == NULL)
{
return ;
}
sList->length = 0;
sList->header.next = NULL;
sList->slider = NULL;
}
int CircleList_Length(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
int ret = -1;
if (list == NULL)
{
return ret;
}
ret = sList->length;
return ret;
}
int CircleList_Insert(CircleList* list, CircleListNode* node, int pos) // O(n)
{
int ret = 0, i=0;
TCircleList* sList = (TCircleList*)list;
if (list == NULL || node== NULL || pos<0)
{
return -1;
}
//if( ret )
{
CircleListNode* current = (CircleListNode*)sList;
for(i=0; (i<pos) && (current->next != NULL); i++)
{
current = current->next;
}
//current->next 0号节点的地址
node->next = current->next; //1
current->next = node; //2
//若第一次插入节点
if( sList->length == 0 )
{
sList->slider = node;
}
sList->length++;
//若头插法 current仍然指向头部
//(原因是:跳0步,没有跳走)
if( current == (CircleListNode*)sList )
{
//获取最后一个元素
CircleListNode* last = CircleList_Get(sList, sList->length - 1);
last->next = current->next; //3
}
}
return ret;
}
CircleListNode* CircleList_Get(CircleList* list, int pos) // O(n)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;
if (list==NULL || pos<0)
{
return NULL;
}
//if( (sList != NULL) && (pos >= 0) && (sList->length > 0) )
{
CircleListNode* current = (CircleListNode*)sList;
for(i=0; i<pos; i++)
{
current = current->next;
}
ret = current->next;
}
return ret;
}
CircleListNode* CircleList_Delete(CircleList* list, int pos) // O(n)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;
if( (sList != NULL) && (pos >= 0) && (sList->length > 0) )
{
CircleListNode* current = (CircleListNode*)sList;
CircleListNode* last = NULL;
for(i=0; i<pos; i++)
{
current = current->next;
}
//若删除第一个元素(头结点)
if( current == (CircleListNode*)sList )
{
last = (CircleListNode*)CircleList_Get(sList, sList->length - 1);
}
//求要删除的元素
ret = current->next;
current->next = ret->next;
sList->length--;
//判断链表是否为空
if( last != NULL )
{
sList->header.next = ret->next;
last->next = ret->next;
}
//若删除的元素为游标所指的元素
if( sList->slider == ret )
{
sList->slider = ret->next;
}
//若删除元素后,链表长度为0
if( sList->length == 0 )
{
sList->header.next = NULL;
sList->slider = NULL;
}
}
return ret;
}
CircleListNode* CircleList_DeleteNode(CircleList* list, CircleListNode* node) // O(n)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
int i = 0;
if( sList != NULL )
{
CircleListNode* current = (CircleListNode*)sList;
//查找node在循环链表中的位置i
for(i=0; i<sList->length; i++)
{
if( current->next == node )
{
ret = current->next;
break;
}
current = current->next;
}
//如果ret找到,根据i去删除
if( ret != NULL )
{
CircleList_Delete(sList, i);
}
}
return ret;
}
CircleListNode* CircleList_Reset(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
if( sList != NULL )
{
sList->slider = sList->header.next;
ret = sList->slider;
}
return ret;
}
CircleListNode* CircleList_Current(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
if( sList != NULL )
{
ret = sList->slider;
}
return ret;
}
//把当前位置返回,并且游标下移
CircleListNode* CircleList_Next(CircleList* list) // O(1)
{
TCircleList* sList = (TCircleList*)list;
CircleListNode* ret = NULL;
if( (sList != NULL) && (sList->slider != NULL) )
{
ret = sList->slider;
sList->slider = ret->next;
}
return ret;
}
传说中的约瑟夫问题.c
#include <stdio.h>
#include <stdlib.h>
#include "CircleList.h"
struct Value
{
CircleListNode header;
int v;
};
void main()
{
int i = 0;
CircleList* list = CircleList_Create();
struct Value v1, v2, v3, v4, v5, v6, v7, v8;
v1.v = 1; v2.v = 2; v3.v = 3; v4.v = 4;
v5.v = 5; v6.v = 6; v7.v = 7; v8.v = 8;
CircleList_Insert(list, (CircleListNode*)&v1, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v2, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v3, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v4, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v5, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v6, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v7, CircleList_Length(list));
CircleList_Insert(list, (CircleListNode*)&v8, CircleList_Length(list));
for(i=0; i<CircleList_Length(list); i++)
{
//获取游标所指元素,然后游标下移
struct Value* pv = (struct Value*)CircleList_Next(list);
printf("%d\n", pv->v);
}
printf("\n");
//重置游标
CircleList_Reset(list);
while( CircleList_Length(list) > 0 )
{
struct Value* pv = NULL;
for(i=1; i<3; i++)
{
CircleList_Next(list);
}
pv = (struct Value*)CircleList_Current(list);
printf("%d\n", pv->v);
CircleList_DeleteNode(list, (CircleListNode*)pv);
}
CircleList_Destroy(list);
system("pause");
return ;
}
基本思想就是,将在业务模型中包含一个节点,这个节点就是链表的节点,然后使用强制转化,实现双方的相互转化。。。
这种思维也让linux内核以C代码实现了C++的面向对象的多态思想。