C - 链表 - 插入元素未更新 - 仅添加最后一个输入元素 [英] C - Linked list - Insert element not updated - Only adding last input element

问题描述

PREFACE:目标是提示用户输入，将每个元素(输入行)添加到链表中.

PREFACE: The goal is to prompt a user for input, adding each element (input line) into a linked list.

我一直在玩一些来自 Learn-C.org 的示例代码，其中显示了一个链表示例.我修改了代码，使其采用字符串"而不是整数.

I have been playing around with some sample code from Learn-C.org, which shows a linked list example. I have modified the code so that it takes "strings" instead of integers.

我的插入功能如下:

void push(node_t * head, char *data) {
    node_t * current = head;

    if(head == NULL) {
      printf("First element ever!
");
    }
    else if(current->data == NULL) {
      current->data = data;
      current->next = NULL;

    }
    else {
      while (current->next != NULL) {
        current = current->next;
        }
      current->next = malloc(sizeof(node_t));
      current->next->data = data;
      current->next->next = NULL;
   }
}

现在，在 MAIN 中，我按如下方式启动列表:

Now, in MAIN, I initiate the list as follows:

node_t * test_list = malloc(sizeof(node_t));

添加元素是通过:

  push(test_list, "FOO");
  push(test_list, "FEE");
  push(test_list, "FAA");

打印列表时，使用print_list(test_list)，我得到以下输出:

When printing the list, using print_list(test_list), I get the following output:

FOO
FEE
FAA

问题

但是，我随后包含了一个 while 循环，该循环提示用户输入并将其添加到链表中.

However, I have then included a while loop that prompts user for input and adds this to the linked list.

char command[120];
int counter = 0;
while(counter < 3) {
    printf("Enter element: ");
    fgets((void *)command, sizeof(command), stdin);
    push(test_list, command);   //Insert
    counter++;
}

然而，这不会将每个元素添加到链接列表中.相反，它将最后一个元素添加到列表中三次.

However, this does not add each element into the link list. Instead, it adds the LAST element into the list three times.

例如，当提供:

Enter element: Argentina
Enter element: Mexico
Enter element: Sweden

列表打印为:

FOO
FEE
FAA
Sweden
Sweden
Sweden

EDIT(添加打印功能)

我的打印功能如下:

void print_list(node_t * head) {
    node_t * current = head;

    printf("**** Printing list ****
");
    while (current != NULL) {
        printf("%s
", current->data);
        current = current->next;
    }
}

我错过了什么，或者:我该如何解决这个问题?任何帮助都受到高度赞赏.

What am I missing, and alternatively: How can I fix this? Any help is highly appreciated.

推荐答案

使用 strdup 返回分配在堆上的字符串的副本.

Use strdup to return a copy of the string allocated on the heap.

strdup() 函数返回一个指向新字符串的指针，该字符串是字符串 s 的副本.新字符串的内存通过 malloc(3) 获得，可以通过 free(3) 释放.

The strdup() function returns a pointer to a new string which is a duplicate of the string s. Memory for the new string is obtained with malloc(3), and can be freed with free(3).

node_t *test_list = malloc(sizeof(node_t));
test_list->next = NULL;
test_list->data = NULL;
while(counter < 3) {
  printf("Enter element: ");
  fgets((void *)command, sizeof(command), stdin);
  push(test_list, strdup(command));   //Insert
  counter++;
}

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