双向循环链表实践---学生管理系统
写在前面
在看Linux源码时，经常会涉及到驱动和设备的匹配，如果想弄清楚匹配过程，就要理解双向循环链表。
这篇文章是理解了Linux的list.h文件后自己的实现应用。
理论知识
实现步骤
链表的常用的节点操作如下：
增加、删除、查找
首先定义一个结构体，存放学生的信息
struct student {
int number;
char id[20]; //学号
char name[20]; //姓名
float score; //成绩
struct student *next;
struct student *prev;
};创建头节点
- 创建头指针
- 初始化头指针
- 分配内存
- 自己指向自己
struct student *head = NULL;
/*create head node*/
void init(void)
{
printf("%s\n", __func__);
head = (struct student *)malloc(sizeof(struct student));
head->next = head;
head->prev = head;
}增加节点
void add_student(void)
{
/*增加一个学生的信息*/
char new_id[20] = {0};
char new_name[20] = {0};
float new_score = 0.00;
memset(new_id, 0, sizeof(new_id));
memset(new_name, 0, sizeof(new_name));
printf("%s\n", __func__);
printf("enter the id:\n");
scanf("%s", new_id);
/*id是唯一的依据，所以要进行去重操作*/
if(have_same_id(new_id)){
printf("hava same id\n");
goto have_same_id;
}
printf("enter the name:\n");
scanf("%s", new_name);
printf("enter the score:\n");
scanf("%f", &new_score);
/*增加新节点核心操作*/
struct student * new_node = (struct student *)malloc(sizeof(struct student));
struct student * last_node = head->prev;
last_node->next = new_node;
new_node->prev = last_node;
head->prev = new_node;
new_node->next = head;
count++;
/*节点信息填充*/
new_node->number = count;
memset(new_node->id, 0, sizeof(new_node->id));
memset(new_node->name, 0, sizeof(new_node->name));
strcpy(new_node->id, new_id);
strcpy(new_node->name, new_name);
new_node->score = new_score;
printf("add student ok!\n");
list_all_student();
have_same_id:
return ;
}#define HAVE_SAME_ID 1
#define NO_SAME_ID 0
int have_same_id(char *id)
{
struct student *pos = NULL;
for(pos = head->next; pos != head; pos = pos->next)
{
if(strcmp(pos->id, id) == 0){
return HAVE_SAME_ID;
}
}
return NO_SAME_ID;
}删除节点
void delete_student()
{
struct student * pos = NULL;
char id[20];
printf("%s\n", __func__);
memset(id, 0, sizeof(id));
/*以ID为唯一凭证*/
printf("enter the id that you want delete:\n");
scanf("%s", id);
//删除节点核心实现
for(pos = head->next; pos != head; pos = pos->next)
{
if(strcmp(pos->id, id) == 0){
printf("delete\t%d\t%s\t\t\t%s\t\t\t%f\n", pos->number, pos->id, pos->name, pos->score);
pos->prev->next = pos->next;
pos->next->prev = pos->prev;
free(pos);
delete_student_fixed_count(); //删除节点后，修复节点中number标记
return;
}
}
printf("no the same id, pleace check it again\n");
}void delete_student_fixed_count(void)
{
struct student *pos = NULL;
int i = 0;
count--;
for(pos = head->next, i = 1; pos != head; pos = pos->next, i++)
{
pos->number = i;
}
i--;
if(i != count){
printf("i = %d\t, count = %d\n", i, count);
printf("count error\n");
}
list_all_student();
}查找节点
查找结点比较简单，根据一个值遍历所有节点即可
示例代码中，以学生ID为唯一参考
void search_student_score(void)
{
struct student * pos = NULL;
char id[20];
printf("%s\n", __func__);
memset(id, 0, sizeof(id));
printf("enter the id that want to search:\n");
scanf("%s", id);
//核心代码
for(pos = head->next; pos != head; pos = pos->next)
{
if(strcmp(pos->id, id) == 0){
printf("find the id:\n");
printf("\tid\t\t\tname\t\t\tsorce\n");
printf("%d\t%s\t\t\t%s\t\t\t%f\n", pos->number, pos->id, pos->name, pos->score);
return;
}
}
printf("sorry, can not find the id info\n");
}释放节点
由于内存空间是使用malloc进行分配的，所有要用free进行手动释放，释放某一个节点比较简单，释放所有节点相对复杂点，其实就是遍历所有节点，并一一删除。
释放一个节点
- 以ID为标记，找到要释放的节点
- 注意修改节点的next和prev节点
- 释放该节点的内存
void delete_student()
{
struct student * pos = NULL;
char id[20];
printf("%s\n", __func__);
memset(id, 0, sizeof(id));
printf("enter the id that you want delete:\n");
scanf("%s", id);
//核心实现
for(pos = head->next; pos != head; pos = pos->next)
{
if(strcmp(pos->id, id) == 0){
printf("delete\t%d\t%s\t\t\t%s\t\t\t%f\n", pos->number, pos->id, pos->name, pos->score);
pos->prev->next = pos->next;
pos->next->prev = pos->prev;
free(pos);
delete_student_fixed_count();
return;
}
}
printf("no the same id, pleace check it again\n");
}删除所有节点
结束程序时，要删除所有分配过的内存，防止内存泄漏
该操作就是遍历所有节点并释放内存
void free_all_memory()
{
struct student * pos = head->next;
printf("%s\n", __func__);
for(; pos != head; )
{
head->next = pos->next;
pos->next->prev = head;
printf("\tdelete node->number = %d\n", pos->number); //显示所有要删除的节点，防止有内存泄露
free(pos);
pos = head->next;
}
printf("\tdelete head node\n");
free(head);
}完整代码
此示例代码，已经实验过，无内存泄漏，所有功能实现。
/*************************
双向循环链表练习
学生管理系统
2018.01.27
cxiaolei
*************************/
#include