Question

我写了这段代码:(上面的结构和下面的函数）我正在尝试这个功能来注册学生并将他删除。

void reg_student(slist *students, clist *courses, int id, int number){
slist *temp;
clist*temp1;
student *reg;
course *addit;
for (temp = students; temp->info->id!=id; temp = temp->next);
reg = temp->info;// the student we want to register.
for (temp1 = courses; temp1->info->number != number; temp1 = temp1->next);
addit = temp1->info;//the course to add.
//adding the course to the student courses list.
reg->courses = add_course(reg->courses, addit->title, addit->number);
//adding the student to the course students list.
addit->students = add_student(addit->students, reg->name, reg->id);

void unreg_student(slist *students, int id, int number){
slist *temp;
clist *temp1;
student *studenttoremove;
course *coursetoremove;
for (temp = students; temp->info->id != id; temp = temp->next);
studenttoremove = temp->info;// the student we want to delete.
for (temp1 = studenttoremove->courses; temp1->info-> number != number; temp1 = temp1->next);
coursetoremove = temp1->info;//the course we want to delete.
studenttoremove->courses = remove_course(studenttoremove->courses, coursetoremove);
temp1->info->students = remove_student(temp1->info->students, studenttoremove);

}

slist* remove_student(slist*students, student* s1){
slist* temp=students,*temp1;
if (temp->info == s1){
    if (!(temp->next)){
        free(temp);
        return NULL;
    }
    temp1 = temp->next;
    free(temp);
    return temp1;
}
for (temp = students; temp->next->info != s1; temp = temp->next);
temp1 = temp->next;
temp = temp1->next;
free(temp1);
return students;

}

clist* remove_course(clist*courses, course * c1){
clist* temp=courses, *temp1;
if (temp->info == c1){
    if (!(temp->next)){
        free(temp);
        return NULL;
    }
    temp1 = temp->next;
    free(temp);
    return temp1;
}
for (temp = courses; temp->next->info != c1; temp = temp->next);
temp1 = temp->next;
temp = temp1->next;
free(temp1);
return courses;

}

`结构是：

    typedef struct course {
    char *title;
    int  number;
    struct slist *students;
} course;

typedef struct slist {
    student      *info;
    struct slist *next;
} slist;

typedef struct clist {
    course       *info;
    struct clist *next;
} clist;

这些功能应该添加和删除学生和课程。寄存器工作正常。但是当我试图删除学生时，该课程将从学生课程列表中删除，但学生不会从课程列表中删除。当我调试它时，我看到删除功能正在获取一个NULL作为学生列表..我不明白为什么。谢谢。

Answer 1

这两个功能的主要问题是在最后，你有temp = temp1->next。它应该是temp->next = temp1->next。

slist* remove_student(slist*students, student* s1){
    slist* temp=students,*temp1;
    if (temp->info == s1){
        if (!(temp->next)){
            free(temp);
            return NULL;
        }
        temp1 = temp->next;
        free(temp);
        return temp1;
    }
    for (temp = students; temp->next->info != s1; temp = temp->next);
    if (!temp->next)
        return students;
    temp1 = temp->next;
    temp->next = temp1->next;
    free(temp1);
    return students;
}

clist* remove_course(clist*courses, course * c1){
    clist* temp=courses, *temp1;
    if (temp->info == c1){
        if (!(temp->next)){
            free(temp);
            return NULL;
        }
        temp1 = temp->next;
        free(temp);
        return temp1;
    }
    for (temp = courses; temp->next->info != c1; temp = temp->next);
    if (!temp->next)
        return courses;
    temp1 = temp->next;
    temp->next = temp1->next;
    free(temp1);
    return courses;
}

编辑：抱歉，我完全错过了。另一个问题出在unreg_student()本身。原因是当调用remove_student()时，您将temp1->info->student作为第一个参数传递，而temp1指向的内存块已被先前调用的remove_course()释放。这意味着您正在玩内存访问冲突。 temp1中存储的内容可能不再是您所期望的，甚至可能无法访问。但是你可以很容易地解决这个问题。只需将unreg_student()的最后一行替换为coursetoremove->students = remove_student(coursetoremove->students, studenttoremove);：

void unreg_student(slist *students, int id, int number){
    slist *temp;
    clist *temp1;
    student *studenttoremove;
    course *coursetoremove;
    for (temp = students; temp->info->id != id; temp = temp->next);
    studenttoremove = temp->info;// the student we want to delete.
    for (temp1 = studenttoremove->courses; temp1->info->number != number; temp1 = temp1->next);
    coursetoremove = temp1->info;//the course we want to delete.
    studenttoremove->courses = remove_course(studenttoremove->courses, coursetoremove);
    coursetoremove->students = remove_student(coursetoremove->students, studenttoremove);
}

陷入链接列表

1 个答案: