想用free释放malloc创建的头结点L内存但是报错了，最后只好将头结点L，指向NULL，请教一下各位，要怎么改进代码呢？

Question

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
#define MAXSIZE 10
#define OK 1
#define ERROR 0
#define T 1
#define F -1
 
typedef int Status;
struct Student {
    int id;
    char name[20];
    float grade;
};
 
typedef struct Dlist {
    Student data;
    struct Dlist* next;
}Dlist,*Zdlist;
 
//创建
Status Cj_List(Zdlist& L) {
    L = (Zdlist)malloc(sizeof(Student));
    if (L) {
        L->next = NULL;
        printf("创建成功!\n");
        return OK;
    }
    printf("创建失败!\a\n");
    return ERROR;
}
 
//插入
Status Cr_List(Zdlist &L ,int i,Student e) {
    Zdlist p ,s;
    p = L;
    int j = 0;                          //判断是否有头结点，无头节点则创建失败。
    while (p && (j < i - 1)) {
        p = p->next;
        ++j;
    }
    if (!p || j > i - 1) {
        printf("插入失败!\a\n");
        return ERROR;
    }
    s = (Zdlist)malloc(sizeof(Student));//插入时先新建头结点
    s->next = NULL;                 //定义p=L用p代替L进行指针遍历,防止丢失头结点
    s->data = e;
    s->next = p->next;           
    p->next = s;
    printf("插入成功!\n");
    return OK;
    
}
 
//查找
Status Cz_List(Zdlist L, Student e) {
    Zdlist p ;
    int i = 1;
    p = L->next;
    while (p && strcmp(p->data.name, e.name) != 0) {  // 比较名字字符
        p = p->next;
        i++;
    }
    if (p) {
        printf("学生数据在第 %d 位\n", i);
        return OK;
    }
    printf("未找到该学生!\a\n");
    return ERROR;
}
 
//取值
Status Qz_List(Zdlist L, int i) {     //找到位置直接输出学生信息
    Zdlist p = L;
    int j = 0;
    while (p && (j < i )) {
        p = p->next;
        ++j;
    }
    if (!p || (j > i )) {
        printf("取值位置不合理!\a\n");
        return ERROR;
    }printf("该学生信息为:学号:%d 姓名:%s 成绩:%.2f\n", p->data.id, p->data.name, p->data.grade);
    return OK;
}
 
//删除
Status Sch_List(Zdlist& L, int i) {
    Zdlist p = L;
    int j = 0;
    while ((p->next) && (j < i - 1)) {
        p = p->next;
        ++j;
    }
    if (!(p->next) || (j > i - 1)) {
        printf("删除的位置不合理!\a\n");
        return ERROR;
    }
    Zdlist q = (Zdlist)malloc(sizeof(Student));
    Dlist* temp = q;
    q = p->next;
    p->next = q->next;
    free (temp);         //使指针指向删除节点的下一个节点，用free将删除节点内存释放
    temp->next = NULL;
    printf("删除成功!\n");
    return OK;
}
 
//输出
Status Sc_List(Zdlist L) {
    Zdlist p = L;
    int sum=0;
    if (!p->next) {
        printf("链表为空!\a\n");
        return ERROR;
    }
    printf("全部学生数据:\n");
    while (p->next!=NULL) {
        p = p->next;
        sum++;      //输出总人数
        printf("学号:%d 姓名:%s 成绩:%.2f\n学生总数量:%d个\n", p->data.id, p->data.name, p->data.grade,sum);
    }
    return OK;
}
 
 
//清空
Status Qk_List(Zdlist& L,int open) {
    if (open != T) {
        printf("内存未被创建!\a\n");
        return ERROR;
    }
    while (L->next!=NULL) {    //调用删除函数遍历清空链表所有元素及释放内存
        Sch_List(L, 1);
    }
    L = NULL;
    printf("清楚数据完成!\n内存已清空\n");
    return OK;
}
 
 
int main() {
    Zdlist L;
    Student e;
    int choose;
    int i;
    int open = F;    //判断内存是否已经创建，防止键盘非法输入造成遍历越界报错异常
    while (1) {
        printf("*******************************\n");
        printf("1.创建\n");
        printf("2.插入\n");
        printf("3.查找\n");
        printf("4.提取\n");
        printf("5.删除\n");
        printf("6.输出\n");
        printf("7.清空\n");
        printf("8.退出\n");
        printf("请选择操作:");
        scanf("%d", &choose);
        printf("\n");
        switch (choose) {
        case 1:
            if (open != F) {
                printf("请勿重复创建!\a\n");
                break;
            }
            Cj_List(L);
            open = T;          //open=T 已申请内存  open=F 内存未被申请
            break;
        case 2:
            if (open != T) {
                printf("内存未被创建!\a\n");
                break;
            }
            printf("输入插入的位置、学号、姓名、成绩(空格隔开)\n");
            scanf("%d %d %s %f", &i, &e.id, &e.name,&e.grade);
            Cr_List(L, i, e);
            break;
        case 3:
            if (open != T) {
                printf("内存未被创建!\a\n");
                break;
            }
            printf("输入需查找学生的姓名:");
            scanf("%s", e.name);
            printf("\n");
            Cz_List(L, e);
            break;
        case 4:
            if (open != T) {
                printf("内存未被创建!\a\n");
                break;
            }
            printf("输入提取的位置\n");
            scanf("%d", &i);
            Qz_List(L, i);
            break;
        case 5:
            if (open != T) {
                printf("内存未被创建!\a\n");
                break;
            }
            printf("输入删除的位置\n");
            scanf("%d", &i);
            Sch_List(L, i);
            break;
        case 6:
            if (open != T) {
                printf("内存未被创建!\a\n");
                break;
            }
            Sc_List(L);
            break;
        case 7:
            Qk_List(L,open);
            open = F;
            break;
        case 8:
            printf("已成功退出！\n");
            system("pause");
            return 0;
        }
    }
}
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原文链接：https://blog.csdn.net/weixin_55797565/article/details/120975844