Question

我有一个名为book的结构和一个链接到struct book的列表。我必须将书籍添加到我的书籍列表中，然后显示列表。我创建了一个函数“printBList”来在屏幕上打印我的列表信息。但是当我试图打印book.id时，我做错了什么，程序停止响应。我相信行“book * b = head-＆gt; book;”和“printf（”书ID％d \ n“，b-＆gt; id）;”是错的，但我找不到我必须写的权利。有人能帮助我吗？

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

#define MAXSTRING 100
#define MAXREVIEWS 100

typedef  enum genres{
    fiction, 
    sientific,
    politics
};

typedef struct
{
    char author[MAXSTRING];
    char title[MAXSTRING];
    enum genres genre;
    int id;
    char reviews[MAXREVIEWS][MAXSTRING];
} book;


typedef struct list 
{
    int BookID;
    struct list * next;
    struct book * book;
} BList;


void printBList(BList * head) 
{
    BList * current = head;
    book *b=head->book;

    while (current != NULL) {
        printf("List ID:: %d\n", current->BookID);
        printf("book ID%d\n", b->id);
        //printf("%d\n", current->BookID);        
        current = current->next;
    }
}


int main()
{
    BList * head = NULL;
    head = malloc(sizeof(BList));
    if (head == NULL) {
        return 1;
    }

    book b={"author 1","title 1",1,22,"review 1"};  

    head->next = NULL;
    head = malloc(sizeof(BList));

    head->BookID = 1;
    head->next = malloc(sizeof(BList)); 
    head->next->BookID = 24;
    head->next->book;
    head->next->next = NULL;

    printBList(head);
    return 0;
}

Answer 1

问题在于打印列表的方式，在这里：

while (current != NULL) {
    printf("List ID:: %d\n", current->BookID);
    printf("book ID%d\n", b->id); // <-- HERE
    current = current->next;
}

您使用的是current，但是您尝试打印已修复的b。

你可能想说：

printf("book ID%d\n", current->book->id);

但还有更多问题：

此外，你打算写：

typedef struct book {
   ..
} book;

在为next创建空间之前，您正在访问head head，此处：

head->next = NULL;
head = malloc(sizeof(BList));

所以改成它：

head = malloc(sizeof(BList));
head->next = NULL;

此外，这一行：

head->next->book;

什么也没做。

接下来，您应该检查警告：

Georgioss-MacBook-Pro:~ gsamaras$ gcc -Wall main.c 
main.c:7:1: warning: typedef requires a name [-Wmissing-declarations]
typedef  enum genres{
^~~~~~~
main.c:34:11: warning: incompatible pointer types initializing 'book *' with an
      expression of type 'struct book *' [-Wincompatible-pointer-types]
    book *b=head->book;
          ^ ~~~~~~~~~~
main.c:53:39: warning: suggest braces around initialization of subobject
      [-Wmissing-braces]
    book b={"author 1","title 1",1,22,"review 1"};  
                                      ^~~~~~~~~~
                                      {         }
main.c:61:17: warning: expression result unused [-Wunused-value]
    head->next->book;
    ~~~~~~~~~~  ^~~~
main.c:53:10: warning: unused variable 'b' [-Wunused-variable]
    book b={"author 1","title 1",1,22,"review 1"};  
         ^
5 warnings generated.

当你输入dede的东西时，你需要给出一个同义词，所以为你的枚举做这个：

typedef  enum genres{
  ..
} genres;

由于reviews是一个2D数组，您可以这样做：

book b={"author 1","title 1",1,22, {"review 1"} };

此外，请不要使用幻数，在这种情况下为1，因为您有enum用于此目的。

然后，我更改了您的main()，将同一本书添加两次，使用不同的列表ID。把所有东西放在一起，我们得到：

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

#define MAXSTRING 100
#define MAXREVIEWS 100

typedef  enum genres{
    fiction, 
    sientific,
    politics
} genres;

typedef struct book
{
    char author[MAXSTRING];
    char title[MAXSTRING];
    enum genres genre;
    int id;
    char reviews[MAXREVIEWS][MAXSTRING];
} book;


typedef struct list 
{
    int BookID;
    struct list * next;
    struct book * book;
} BList;


void printBList(BList * head) 
{
    BList * current = head;

    while (current != NULL) {
        printf("List ID:: %d\n", current->BookID);
        printf("book ID%d\n", current->book->id);
        current = current->next;
    }
}


int main()
{
    BList * head = NULL;
    head = malloc(sizeof(BList));
    if (head == NULL) {
        return 1;
    }

    book b={"author 1","title 1", sientific ,22,{"review 1"}};  

    head->next = NULL;
    head->BookID = 1;
    head->book = &b;

    head->next = malloc(sizeof(BList)); 
    head->next->BookID = 24;
    head->next->book = &b;
    head->next->next = NULL;

    printBList(head);
    return 0;
}

输出：

Georgioss-MacBook-Pro:~ gsamaras$ gcc -Wall main.c 
Georgioss-MacBook-Pro:~ gsamaras$ ./a.out 
List ID:: 1
book ID22
List ID:: 24
book ID22

PS：

不要忘记取消分配您动态分配的空间。做这与free()。
检查malloc()是否成功，这是一个很好的做法检查其返回值是否为NULL（表示失败）。阅读更多在 How detect malloc failure?

C中的结构内部列表 - 显示链接列表中存在的结构的成员

1 个答案: