c-Glibc损坏的双链接列表

Question

我有一个程序可以读取文本文件，并将其分为章节和段落结构。

struct paragraph
{
   char** lines;
   int numLines;
};
struct chapter
{
   struct paragraph** paragraphs;
   int numParagraphs;
};
struct book
{
   struct chapter** chapters;
   int numChapters;
};

以下是有问题的代码片段，特别是realloc（）语句：

//int numChapters = -1;
//char**** book = (void*)0;
struct book* books = malloc(sizeof(struct book*));
books->chapters = malloc(sizeof(struct chapter));
books->numChapters = -1;
//char*** nextChapter;
struct chapter* nextChapter = malloc(sizeof(struct chapter));

while ( (nextChapter = readChapter(bookFile))->paragraphs[0] )
{
    if (++(books->numChapters) > 0)
    {
        books = realloc(books, sizeof(struct chapter*)*books->numChapters);
        books->chapters[books->numChapters - 1] = nextChapter;
    }
}
books = realloc(books, sizeof(struct chapter*)*books->numChapters);
books->chapters[books->numChapters] = (void*)0;
return books;

这个代码片段中调用的函数应该可以正常工作，至少我相信这一点。这一定是记忆管理不善的问题。谢谢你的建议！

我应该提到的是，它通读了前几章，然后出现了错误。

Answer 1

也许您不需要在每个结构中使用两个指针？你有用于章节和段落的数组-不需要使用双指针。

提供的代码更有可能使用数组，而不是列表。所以，若你们试图使用列表，我在答案的末尾提到了它们。否则，修复它以使用数组会更简单，这是第一个问题：

if (++(books->numChapters) > 0)
{
    /* here books are reallocated */
    books = realloc(books, sizeof(struct chapter*)*books->numChapters);
    /* but here chapters which had not been reallocated are acessed */
    books->chapters[books->numChapters - 1] = nextChapter;
}

如果你有新的章节，为什么你需要重新分配书籍？只是realloc书籍->章节：

if (++(books->numChapters) > 0)
{
    books->chapters = realloc(books->chapters, sizeof(struct chapter*)*books->numChapters);
    books->chapters[books->numChapters - 1] = nextChapter;
}

最后还是同样的问题：

/* books are reallocated, size is bad - reallocated to size of numChapters * (pointer size) */
books = realloc(books, sizeof(struct chapter*)*books->numChapters);
/* perhaps access to non-allocated memory here */
books->chapters[books->numChapters] = (void*)0;

应为：

books->chapters = realloc(books->chapters, sizeof(struct chapter)*books->numChapters);
// books->chapters[books->numChapters] = (void*)0;

不需要为最后一个元素指定NULL，因为章节的大小为numChapters，而访问元素numChapters会导致访问未分配的内存，崩溃。

上面的所有代码都使用了数组的概念，而不是链表。

要将其切换到链表，需要使用以下结构：

struct paragraph
{
   struct paragraph *next; // <<-- this field is used to build
                           //      linked list of paragraphs
   char* lines;
   int numLines;
};
struct chapter
{
   struct chapter *next; // <<-- this field is used to build 
                         //      linked list of chapters
   struct paragraph* paragraphs;
   int numParagraphs;
};
struct book
{
   struct chapter* chapters;
   int numChapters;
};

当然，需要适当的分配和分配"下一个"指针。