c - C 中的结构内部列表 - 显示链接列表中存在的结构的成员

Question

我有一个名为 book 的结构和一个链接到结构 book 的列表。我必须将书籍添加到我的书籍列表中，然后显示该列表。我创建了一个函数“printBList”来在屏幕上打印我的列表的信息。但是当我尝试打印 book.id 时我做错了，程序停止响应。我相信“book *b=head->book;”这行和 "printf("图书 ID%d\n", b->id);"是错的，但我找不到我必须如何写才对。有人可以帮助我吗？

#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

问题出在打印列表的方式上，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，但您尝试打印已修复的b。

你可能想说的是:

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

---

但还有更多问题:

此外，您打算写:

typedef struct book {
   ..
} book;

在为 head 创建空间之前，您正在访问 head 的 next，此处:

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

所以将其更改为:

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

此外，这一行:

head->next->book;

什么也不做。

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.

当您键入某些内容时，您需要给出一个同义词，因此请为您的枚举执行此操作:

typedef  enum genres{
  ..
} genres;

由于 reviews 是一个二维数组，因此您可以这样做:

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

此外，请勿使用魔数(Magic Number)，例如本例中的 1，因为您有一个用于此目的的枚举。

---

然后，我对您的 main() 进行了一些更改，以使用不同的列表 ID 添加同一本书两次。将所有内容放在一起，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:

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