卡住了鏈表

Question

我寫了下面這段代碼:(上面的結構和下面的函數） 我試着用這個函數註冊一個學生並刪除他。

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; 

}

`的結構是：

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; 

這些功能應該添加和刪除學生和課程。 該寄存器工作正常。但是當我試圖刪除學生時，課程將從學生課程列表中刪除，但學生不會從課程列表中刪除。當我調試它時，我看到刪除函數獲得一個NULL作爲學生名單..我不明白爲什麼。 謝謝。

Answer 1

這兩個功能的主要問題是在最後，你有temp = temp1->next。它應該是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; 
} 

編輯：對不起，我完全錯過了。另一個問題在unreg_student()本身。原因是當調用remove_student()時，您通過temp1->info->student作爲第一個參數，而由temp1指向的內存塊已被先前稱爲remove_course()釋放。這意味着你正在玩內存訪問衝突。存儲在temp1中的內容可能不再是您所期望的，甚至可能無法訪問。但是你可以很容易地解決這個問題。只需更換的unreg_student()到coursetoremove->students = remove_student(coursetoremove->students, studenttoremove);最後一行：

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); 
}