C：链表和 free() - 示例错误？

Question

学习 Prata 的《C Primer Plus》第 6 版时，我发现了清单 17.2 的链表示例，该示例复制在本文下方。我对他再次释放内存的部分感到困惑。他不是在他的例子中释放指向下一个列表的指针吗？最后，他将current设置为head，使current指向第一个结构体的起始内存地址。然后他释放 current 并设置 current=current->next，但是 current->next 不应该再包含任何地址，因为 current 被释放了？运行通过 CodeBlocks 的程序工作正常，但在 CodeBlocks 中调试 free() while 循环时，出现段错误。我相信我的理解是正确的，程序有问题，对吧？谢谢你。

/* films2.c -- using a linked list of structures */
#include <stdio.h>
#include <stdlib.h> /* has the malloc prototype */
#include <string.h> /* has the strcpy prototype */
#define TSIZE 45 /* size of array to hold title */
struct film
{
    char title[TSIZE];
    int rating;
    struct film * next; /* points to next struct in list */
};
char * s_gets(char * st, int n);
int main(void)
{
    struct film * head = NULL;
    struct film * prev, * current;
    char input[TSIZE];
    /* Gather and store information */
    puts("Enter first movie title:");
    while (s_gets(input, TSIZE) != NULL && input[0] != '[=10=]')
    {
        current = (struct film *) malloc(sizeof(struct film));
        if (head == NULL) /* first structure */
            head = current;
        else /* subsequent structures */
            prev->next = current;
        current->next = NULL;
        strcpy(current->title, input);
        puts("Enter your rating <0-10>:");
        scanf("%d", &current->rating);
        while(getchar() != '\n')
            continue;
        puts("Enter next movie title (empty line to stop):");
        prev = current;
    }
    /* Show list of movies */
    if (head == NULL)
        printf("No data entered. ");
    else
        printf ("Here is the movie list:\n");
    current = head;
    while (current != NULL)
    {
        printf("Movie: %s Rating: %d\n",
               current->title, current->rating);
        current = current->next;
    }
    /* Program done, so free allocated memory */
    current = head;
    while (current != NULL)
    {
        free(current);
        current = current->next;
    }
    printf("Bye!\n");
    return 0;
}
char * s_gets(char * st, int n)
{
    char * ret_val;
    char * find;
    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        find = strchr(st, '\n'); // look for newline
        if (find) // if the address is not NULL,
            *find = '[=10=]'; // place a null character there
        else
            while (getchar() != '\n')
                continue; // dispose of rest of line
    }
    return ret_val;
}

Answer 1

current = head;
while (current != NULL)
{
    free(current);
    current = current->next;
}

but current->next shouldn't contain any address anymore because current is freed?

你的假设是正确的，你正在尝试访问一个已经删除的节点，这就是你的代码段错误的原因，而是使用一个临时节点，在这种情况下你可以重用 head:

current = head;
while (current != NULL)
{
    head = current->next;
    free(current);
    current = head;
}

Running the program via CodeBlocks works fine ...

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C：链表和 free() - 示例错误？

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