鏈接列表：在第二次插入後將功能點插入自身

Question

我正在處理鏈接列表，並且我要做一個插入函數。該列表是從包含學生姓名和分數的文件創建的，並且按照排序的方式創建，第一次嘗試我插入一個新節點即可，但第二次嘗試使新節點指向自身，而不是指向null或節點它之前被插入。我似乎無法找到導致節點指向自身的那一行，而它在第一次嘗試中不會發生！

typedef struct student 
{ 
    char name[20]; 
    int score;  
    struct student *next; 
} Student_Data_Type; 

Student_Data_Type *insert(Student_Data_Type *head, Student_Data_Type *p) 
{ 
    if(head == NULL)//if the head is empty then create list 
    { 
     head = Readfromfile(head); 
    } 
    Student_Data_Type *bufferStack = head; 
    Student_Data_Type *prev; 
    prev = malloc(sizeof(Student_Data_Type)); 
    bool inserted = false; 
    while(bufferStack->next != NULL && 
     strcmp(bufferStack->next->name, p->name) < 0) 

    { 
     bufferStack = bufferStack->next; 
    } 
    p->next = bufferStack->next; 
    bufferStack->next = p; 
    printf("[####] ADDED %s %d\n",bufferStack->next->name, bufferStack->next->score);//Second try says pointing to the same node 
    prev = bufferStack->next; 
    printf("[##] AND IS POINTING TO %s %d\n", prev->next->name, prev->next->score); 
    inserted = true; 
    return head; 
} 

這裏是第一和第二插入輸出： -

//This is the initial list created from the file 
[###] DISPLAYING NAMES AND SCORE OF STUDENTS:- 
[###] ChenZhiheng <-----> 67 
[###] GaoSuxiang <-----> 89 
[###] MaQianli <-----> 90 
[###] ZhangCheng <-----> 95 
1.create list(read from file) 
2.display all records 
3.insert a record 
4.delete a record 
5.query 
0.exit 

//INSERT ONE 
[###]ENTER NAME PLZ: Noor 
[###] ENTER SCORE: 88 
[####] ADDED Noor 88 
[##] AND IS POINTING TO ZhangCheng 95 
1.create list(read from file) 
2.display all records 
3.insert a record 
....... 

//NOW DISPLAYING THE LIST AFTER INSERTING:- 
[###] DISPLAYING NAMES AND SCORE OF STUDENTS:- 
[###] ChenZhiheng <-----> 67 
[###] GaoSuxiang <-----> 89 
[###] MaQianli <-----> 90 
[###] Noor <-----> 88 
[###] ZhangCheng <-----> 95 
1.create list(read from file) 
...... 
//THEN THE SECOND INSERT TRY 
[###]ENTER NAME PLZ: Layla 
[###] ENTER SCORE: 90 
[####] ADDED Layla 90 
[##] AND IS POINTING TO MaQianli 90 
1.create list(read from file) 
...... 
//THEN I CALL MY DISLAY FUNCTION AGAIN AND THIS IS THE OUTPUT: 
[###] DISPLAYING NAMES AND SCORE OF STUDENTS:- 
[###] ChenZhiheng <-----> 67 
[###] GaoSuxiang <-----> 89 
[###] Layla <-----> 90 
[###] MaQianli <-----> 90 
[###] Layla <-----> 90 
[###] MaQianli <-----> 90 
[###] Layla <-----> 90 
[###] MaQianli <-----> 90 
[###] Layla <-----> 90 
[###] MaQianli <-----> 90 
....AND FOREVER LOOP,... 

//HERE IS MY DISPLAY FUNCTION 
void DisplayAll(Student_Data_Type *head) 
{ 
Student_Data_Type *stackbuffer = head; 
printf("[###] DISPLAYING NAMES AND SCORE OF STUDENTS:- \n"); 
while(stackbuffer != NULL) 
    { 
    printf("[###] %s <-----> %d\n", stackbuffer->name, stackbuffer->score); 
    stackbuffer = stackbuffer->next; 
} 

} 

Answer 1

你的整個prev未使用，使用malloc爲它浪費內存。在您的printf聲明中，您使用的是prev，這實際上是您的原始p，因此prev->next是您的原始bufferStack->next，它可能爲空或可能是您不打算的其他東西。

由於您的代碼現在，刪除任何使用prev它應該工作。您的插入代碼似乎是正確的

小號：也刪除inserted，因爲它不使用。

---

傻努爾...的錯誤是在你沒有告訴我們的一部分，你的情況下3：

int main() 
{ 
Student_Data_Type *head,*p; 
    ... 
    case 3:  
      ... 
      strcpy(p->name, Student_Insert); /// <-- copy where???? 
      p->score = Score_Insert; 
      head = insert(head, p); 
      break; 

現在，這裏是爲p分配的內存???幸運的是，您沒有得到分段錯誤，因爲p未初始化（它已初始化，但這是因爲您首先執行了查詢）。