雖然循環覆蓋C鏈接列表的頭節點在C

Question

所以我認爲發生了什麼是我的頭節點不斷被覆蓋，但我不知道爲什麼。如果我刪除while循環，並且只是放入這樣的東西，它的工作就好了。

head = addItem(head, "item one"); 
head = addBack(head, "item two"); 

print(head); 

下面是代碼，因爲它是現在，下面我將包含頭函數與函數。請注意，我所有的菜單項目都沒有在循環中，一直在堅持讓鏈接列表正確一段時間。預先感謝您提供任何提示或建議。

主營：

#include <stdio.h> 
#include <string.h> 
#include <stdlib.h> 
#include "functions.h" 

int menu(); 
void print(node *head); 
node* addItem(node *head, char *item); 
node* addBack(node *head, char *item); 


int main() 
{ 
    int selection; 
    char *item; 
    node* head = NULL; 
    char junk; 

    // Run the menu, and do something based on the selection 
    do { 
     selection = menu(); 
     // If they choose a number that's not between 1 and 3, or 0 
     if (selection > 3) { 
      printf("Please select a valid option\n"); 
     } 
     // If they enter 1, add an item to the list 
     else if (selection == 1) { 
      printf("Enter your list item: "); 
      // scanf leftover characters so fgets will work 
      scanf("%c", &junk); 
      fgets(item, 100, stdin); 
      if (head == NULL) { 
       head = addItem(head, item); 
      } 
      else if (head != NULL) { 
       addBack(head, item); 
      } 
     } 
     else if (selection == 3) { 
      // Print remaining items 
      print(head); 
     } 
    } while (selection != 0); 

return 0; 

} 

編輯：忘了補充在頭文件的功能。

struct node 
{ 
    char *item; 
    struct node *next; 
}; 

typedef struct node node; 


// Menu of choices, returns selection 
int menu() 
{ 
    int selection; 

    printf("\nChoose an option:\n1: Enter a list item \ 
    \n2: Delete a list item\n3: Print remaining items \ 
    \n0: Quit\n\n"); 
    scanf("%d", &selection); 

    return selection; 
} 

node* addItem(node *head, char *item) 
{ 
    node *tmp; 

    tmp = malloc(sizeof(node)); 
    tmp->item = item; 
    tmp->next = head; 
    head = tmp; 


    return head; 
} 

node* addBack(node *head, char *item) 
{ 

    node *tmp, *p; 
    tmp = malloc(sizeof(node)); 
    tmp->item = item; 
    p = head; 
    while (p->next != NULL) { 
     p = p->next; 
    } 
    p->next = tmp; 
    tmp->next = NULL; 

    return head; 
} 

void print(node* head) 
{ 
    node *tmp; 
    tmp = head; 
    if (tmp == NULL) { 
     printf("Add an item first, list is empty\n"); 
     exit(0); 
    } 
    while(tmp != NULL) 
    { 
     printf("%s\n ", tmp->item); 
     tmp = tmp->next; 
    } 
} 

Answer 1

通過使用具有自動存儲持續時間item，其是不確定unintialized變量的值調用未定義行爲。

在讀取輸入之前分配足夠的緩衝區。

else if (selection == 1) { 
    printf("Enter your list item: "); 
    // scanf leftover characters so fgets will work 
    scanf("%c", &junk); 
    /* add from here */ 
    item = malloc(100); 
    if (item == NULL) { 
     perror("malloc"); 
     return 1; 
    } 
    /* add until here */ 
    fgets(item, 100, stdin); 
    if (head == NULL) { 
     head = addItem(head, item); 
    } 
    else if (head != NULL) { 
     addBack(head, item); 
    } 
}