数组最大的问题，就是不支持动态的扩缩容，它是静态内存分配的，一旦分配完成，其容量是固定的。为了支持学生的动态增长，这里可以引入链表。
链表
在C语言中，链表是一种常用的数据结构，它由一系列的节点组成，每个节点包含数据和指向下一个节点的指针。
链表的关键点：
- 节点(Node): 链表中的每个元素称为节点。每个节点通常包含两个部分：数据(Data)和指向另一个节点的指针(Next)。
- 头指针(Head Pointer)：一个指针，它指向链表的第一个节点。这是链表的起点，通过头指针可以遍历整个链表。
- 尾节点(Tail Node)：链表的最后一个节点，并不是一个独立的指针，而是链表中的一个节点，其指针部分指向NULL，表示链表的结束。
学生信息的结构体可以重新定义为：
typedef struct student {
int id; // 学号
char name[MAX_NAME_LEN]; // 姓名
float score; // 成绩
struct student *next; //这里不能够使用 Student *next原因是Student还未定义。
} Student;
链表实现完整代码
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h> // for access() function
#define MAX_NAME_LEN 50
#define STUDENT_SYSTEM "student_system"
typedef struct student {
int id; // 学号
char name[MAX_NAME_LEN]; // 姓名
float score; // 成绩
struct student *next;
} Student;
struct student_db {
Student *header; // 后续指向学生信息链表头部的指针
int student_count; // 学生数量
};
struct student_db stu_db = {
.header = NULL,
.student_count = 0
};
int write_student_info(Student *s)
{
FILE *fp = fopen(STUDENT_SYSTEM, "a");
if (fp == NULL) {
printf("fopen student_system failed!\n");
return 1;
}
fprintf(fp, "%-4d %-10s %-.2f\n", s->id, s->name, s->score);
fclose(fp);
return 0;
}
int check_if_student_exsit(int id)
{
Student *cur= stu_db.header;
while(cur!= NULL) {
if(cur->id == id) {
return 1;
}
cur = cur->next;
}
return 0;
}
Student *init_node(int id, char *name, int score)
{
Student *new_s;
new_s = malloc(sizeof(Student));
if (new_s == NULL) {
printf("malloc Student failed!\n");
exit(-1);
}
new_s->next = NULL;
new_s->id = id;
strcpy(new_s->name, name);
new_s->score = score;
return new_s;
}
void add_student()
{
Student s, *cur, *new_s;
printf("Enter student ID: ");
scanf("%d", &s.id);
printf("Enter student name: ");
scanf("%s", s.name);
s.score = 0.0; // 初始成绩设置为0
if (!check_if_student_exsit(s.id)) {
cur = stu_db.header;
if (cur) {
while(cur) {
if (cur->next == NULL) {
new_s = init_node(s.id, s.name, s.score);
cur->next = new_s;
break;
}
cur = cur->next;
}
} else {
new_s = init_node(s.id, s.name, s.score);
stu_db.header = new_s;
}
stu_db.student_count++;
printf("Student added successfully, all student: %d!\n", stu_db.student_count);
write_student_info(&s);
} else {
printf("student has in db, do nothing!\n");
}
}
void print_title()
{
printf("%-4s %-10s %-5s\n", "ID", "Name", "Score");
}
void display_all_students()
{
Student *cur;
printf("-------- All students info --------\n");
if (stu_db.student_count == 0) {
printf("No students!\n");
} else {
print_title();
cur = stu_db.header;
while (cur) {
printf("%-4d %-10s %-.2f\n", cur->id, cur->name, cur->score);
cur = cur->next;
}
}
printf("-------- End -----------\n");
}
void find_student_by_id()
{
int id;
printf("Enter student ID to search: ");
scanf("%d", &id);
Student *cur = stu_db.header;
while (cur) {
if (cur->id == id) {
printf("%-4d %-10s %-.2f\n", cur->id, cur->name, cur->score);
return;
}
cur = cur->next;
}
printf("Student with ID %d not found!\n", id);
}
void find_student_by_name()
{
int is_find = 0;
char name[MAX_NAME_LEN];
printf("Enter student name to search: ");
scanf("%s", name);
Student *cur = stu_db.header;
while (cur) {
if(strcmp(cur->name, name) == 0) {
printf("%-4d %-10s %-.2f\n", cur->id, cur->name, cur->score);
is_find = 1;
}
cur = cur->next;
}
if (is_find == 0) {
printf("Student with name %s not found!\n", name);
}
}
void add_score()
{
int id;
float score;
printf("Enter student ID: ");
scanf("%d", &id);
printf("Enter student score: ");
scanf("%f", &score);
Student *cur = stu_db.header;
while (cur) {
if(cur->id == id) {
cur->score = score;
printf("Score added successfully!\n");
return;
}
cur = cur->next;
}
printf("Student with ID %d not found!\n", id);
}
void display_average_score()
{
float total = 0.0;
Student *cur = stu_db.header;
while (cur) {
total += cur->score;
cur = cur->next;
}
printf("Average score of all students: %.2f\n", total / stu_db.student_count);
}
int init_student_info()
{
if(access(STUDENT_SYSTEM, F_OK) != 0) { // 文件不存在
return 0;
}
FILE *fp = fopen(STUDENT_SYSTEM, "r");
if (fp == NULL) {
printf("fopen student_system failed!\n");
return 1;
}
#define BUF_SIZE 1024
char buf[BUF_SIZE];
Student *s, *current;
while(fgets(buf, BUF_SIZE - 1, fp) != NULL) {
s = malloc(sizeof(Student));
if (s == NULL) {
printf("malloc Student failed!\n");
exit(-1);
}
s->next = NULL;
sscanf(buf, "%d %s %f\n", &s->id, s->name, &s->score);
stu_db.student_count++;
if (stu_db.header == NULL) {
stu_db.header = s;
current = s;
} else {
current->next = s;
current = s;
}
}
fclose(fp);
return 0;
}
int main()
{
int choice;
int ret;
ret = init_student_info();
if (ret) {
printf("init_student_info failed!\n");
return 1;
}
display_all_students();
do {
printf("\nStudent Score Management System\n");
printf("1. Add Student\n");
printf("2. Display All Students\n");
printf("3. Find Student by ID\n");
printf("4. Find Student by Name\n");
printf("5. Add Score\n");
printf("6. Display Average Score\n");
printf("7. Exit\n");
printf("Enter your choice: ");
scanf("%d", &choice);
switch(choice) {
case 1:
add_student();
break;
case 2:
display_all_students();
break;
case 3:
find_student_by_id();
break;
case 4:
find_student_by_name();
break;
case 5:
add_score();
break;
case 6:
display_average_score();
break;
case 7:
printf("Exiting...\n");
break;
default:
printf("Invalid choice!\n");
}
} while(choice != 7);
return 0;
}
总结
通过链表重构学生成绩管理系统，学生上限数除了受限于内存，其他不受限制。链表相较于数组，它有灵活的扩展的优势，但是它的内存不是连续的，访问性能比不上数组。
虽然当前数组实现的查询，也是遍历数组，但是这里是可以进行排序优化查询的，但是链表不行。
在高性能转发场景中，比如dpdk场景中，使用的还是数组。
