Question

所以我认为发生的事情是我的头节点一直被覆盖，但我不确定为什么。如果我删除while循环并只是输入类似的东西它就可以了。

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

print(head);

这是现在的代码，下面我将包含带有函数的头文件。请注意我的所有菜单项目都不在循环中，现在已经停留在获取链接列表一段时间了。提前感谢任何提示或建议。

主：

#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;

}

编辑：忘记在头文件中添加功能。

    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

您使用具有自动存储时间item的未初始化变量值来调用未定义行为，这是不确定的。

在读取输入之前分配足够的缓冲区。

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);
    }
}

while循环覆盖C中链表的头节点

1 个答案: