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;

此代码段中调用的函数应该可以正常工作，至少我是依赖于这个事实。这是一个记忆管理不善的问题。谢谢你的建议！

我应该提一下，它会通读前几章，然后就会出错。

Answer 1

也许你不需要在每个结构中使用两次指针？你有章节的数组，段落 - 不需要使用两次指针。

提供的代码更有可能使用数组，而不是列表。因此，如果您正在尝试使用列表 - 我在答案结束时提到了它们。否则，修复它以使用数组更简单，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;

}

如果您有新章节，那么为什么需要重新分配书籍？只需重新分配书籍 - >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;

应该是：

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分配NULL，因为章节的大小为numChapters，访问元素numChapters导致访问非分配的内存，崩溃。

上面的所有代码都使用了数组的概念，而不是链接列表。

要将其切换到链接列表，必须使用以下结构：

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“下一个”指针的分配。

Glibc损坏的双链表

1 个答案: