将指针传递给C中的递归函数

Question

我刚刚开始学习C语言,并遇到了一些困难:

下面列出的代码给出了以下错误:

附加到程序:`/ workfolder/cocoa/c_stuff/bookshelf/build/Debug/bookshelf',进程
1674.
无法访问地址0xa0df194的内存无法访问地址0xa0df194的内存

// code start

#define MAX_NAME_LENGTH 200
#define MAX_AUTHOR_LENGTH 200
#define MAX_DESCRIPTION_LENGTH 1000
#define MAX_PUBLISHER 200
#define MAX_ISBN 50


//structures<
typedef struct {
    char title[MAX_NAME_LENGTH];
    char author[MAX_AUTHOR_LENGTH];
    char ISBN[MAX_ISBN];
    char description[MAX_DESCRIPTION_LENGTH];
    char publisher[MAX_PUBLISHER];
} Book;


void getUserInput(Book *s[])
{   
    printf("what is the book's title ?\n");
    fgets(s[book_count]->title, MAX_NAME_LENGTH, stdin);

    printf("what is the author's name?\n");
    fgets(s[book_count]->author, MAX_AUTHOR_LENGTH, stdin);

    printf("what is the ISBN?\n");
    fgets(s[book_count]->ISBN, MAX_ISBN, stdin);

    printf("write a short description\n");
    fgets(s[book_count]->description, MAX_DESCRIPTION_LENGTH, stdin);

    printf("what is the book's publisher\n");
    fgets(s[book_count]->publisher, MAX_PUBLISHER, stdin);

    printf("want to add another book ? Y\\N\n");

    book_count++;

    if(tolower(fgetc(stdin)) == 'y') 
    {
        return getUserInput(s);
    } 
    else 
    {
        return;
    }
}


int main (int argc, const char * argv[]) {
    // insert code here...
    Book *book_shelf[100];

    if((book_shelf[0] = (Book *)malloc(sizeof(Book))) == NULL)
    {
        exit(1);
    }

    getUserInput(book_shelf);

    return 0;
}

代码编译正确,第一次运行正常(所有问题都被提出,结构接收数据); 但是当用户键入"y"以添加另一本书时,会发生mem错误.

任何错误发生的想法？

提前致谢!

Answer 1

你只为main中的第一本书分配了内存 - 之后它试图写入数组中的下一个插槽,它不指向已分配的内存块,给你一个seg-fault.您将不得不为要阅读的每本书分配内存.

另外,由于C不知道数组有多长,因此必须将该信息传递给函数调用.(而且我没有看到你在哪里定义book_count.)

您可以尝试以下这些方面:

void getUserInput(Book *s[], int *book_count, int max_book_count)
{
   if (book_count == max_book_count) return; // If we've filled all the slots, we can't add anymore without causing trouble.
   s[book_count] = malloc(sizeof(Book));

   ..

   if(tolower(fgetc(stdin)) == 'y') 
   {
       (*book_count)++;
       getUserInput(s, book_count, max_book_count);
   } 
   return;
}

int main (int argc, const char * argv[]) {
    // insert code here...
    Book *book_shelf[100];

    int book_count = 0;
    getUserInput(book_shelf, &book_count, 100);
    // Make sure to free all the malloc'd data
}

在这种情况下更好的是,只使用循环并跳过整个递归步骤.

int main (int argc, const char * argv[]) {
    // insert code here...
    Book *book_shelf[100];

    char response = 'y';
    int book_count = 0;
    while (book_count < 100 && response == 'y')
    {
        book_shelf = malloc(sizeof(Book));
        response = getUserInput(book_shelf[book_count++]);
    }
    // make sure to free all the allocated data!
}

char getUserInput(Book *book)
{
   // write input straight to book
   printf("what is the book's title ?\n");
   fgets(book->title, MAX_NAME_LENGTH, stdin);

   ...

   return tolower(fgetc(stdin));
}