C 中的计数器问题和段错误(核心转储)

Question

我目前正在用 C 进行编码，并且在尝试选择性地搜索电影信息/评级结构的链接列表时遇到困难。到目前为止，我刚刚获得了段错误核心转储。我当前的算法基本上 while 循环 current = current->next 除非它在链表中达到 NULL。如果用户输入与链接列表中的标题信息匹配，它将打印出电影详细信息(通过 show_struct())。

但说实话，我希望能够解决这个问题，同时还实现如果用户输入不在链接列表中的电影标题，它将打印出:“数据库中不存在电影。 ”

此外，当我将新电影更新到链接列表中时，计数器也不会增加。它一直停留在 1。有什么想法吗？

这是我到目前为止的代码:

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

struct movie_node {
    char title[250];
    int year;
    unsigned char rating;
    struct movie_node *next;
};

typedef struct movie_node movie_t;

movie_t *first;
movie_t *current;
movie_t *new;
movie_t *make_structure(void);

void fill_structure(movie_t *a); 
void show_structure(movie_t *a);


int main()
{
    int counter = 0;
    char traverse = 1;
    char maininput[1];
    char searchinput[250];  
while (traverse)
{
    printf("%d Movie(s) in the database. Update, Search, or Quit (U/S/Q): ", counter);
    scanf("%1s", maininput);

    if (strcmp("U", maininput) == 0)
    {
        if (counter == 0)
            {
            first = make_structure();
            current = first;
            }               
        else
            {
            new = make_structure();
            current->next=new;
            current=new;
            }
        counter++;            //COUNTER DOESN'T INCREMENT
        fill_structure(current);
        current->next = NULL;
        printf("Movie %s is added to the database.\n\n", current->title);
    }
    if (strcmp("S", maininput) == 0)
    {

        printf("Name of the movie: ");
        scanf(" %[^\n]%*c", searchinput);
        current = first;

        do
        { 
            current=current->next;
            if (strcmp(searchinput, current->title) == 0)  //PROBLEM LIES HERE
                {show_structure(current);}
        } while(current != NULL);
    }
    if (strcmp("Q", maininput) == 0)
    {
        traverse = 0;
    }           
}
return 0;
}

movie_t *make_structure(void)
    {
    movie_t *a;
    a = (movie_t *)malloc(sizeof(movie_t));
    return a;
    }

void fill_structure(movie_t *a)
    {
    printf("Name of the movie: ");
    scanf(" %[^\n]%*c", a->title);
    printf("Year: ");
    scanf("%d", &a->year);
    printf("Rating: ");
    scanf("%hhu", &a->rating);
    }

void show_structure(movie_t *a)
    {
    printf("Year: %d ", a->year);
    printf("Rating: %hhu", a->rating);
    }

现在的输出是这样的:

0 Movie(s) in the database. Update, Search, or Quit (U/S/Q): U
Name of the movie: Pulp Fiction
Year: 1994
Rating: 5
Movie Pulp Fiction is added to the database.

1 Movie(s) in the database. Update, Search, or Quit (U/S/Q): U
Name of the movie: Forrest Gump
Year: 1994
Rating: 5
Movie Forrest Gump is added to the database.

1 Movie(s) in the database. Update, Search, or Quit (U/S/Q): S
Name of the movie: Pulp Fiction
Segmentation fault (core dumped)

Answer 1

考虑一下这段代码:

do
        { 
            current=current->next;
            if (strcmp(searchinput, current->title) == 0)  //PROBLEM LIES HERE
                {show_structure(current);}
        } while(current != NULL);

当 current 是最后一个元素时，它不为 null。你进入循环的顶部，将current设置为current->next，即null，然后尝试访问current->title。但当前为NULL。这是一个问题。这样会更好:

current = first;
while(current != NULL) { 
    if (strcmp(searchinput, current->title) == 0)
        show_structure(current);
    current=current->next;
}