Question

当我试图释放一个malloc的对象时，运行valgrind似乎暗示我让事情变得更糟。例如，这是我的代码：

for(next_token = TKGetNextToken(tokenizer); next_token != NULL; next_token = TKGetNextToken(tokenizer))
        {
            ItemType* item = malloc(sizeof(ItemType));
            item->data = to_lower(next_token);
            item->fileName = filename;
            item->occ = 1;
            HM_Put(hm, item);
            free(next_token);
        }

现在，通过上面的代码，我被告知字节肯定会丢失在item是malloc的行上。但是，如果我在free（next_token）下添加free（item），那么不仅会保留那个肯定丢失的语句，而且我会在堆摘要之前收到大量的无效读取。如果有人能给我一些帮助，我完全不知道如何解决这个问题。感谢

Answer 1

我猜next_token是一个字符串，to_lower不会创建新字符串。这意味着在释放next_token之后item->data仍指向那个自由的记忆。

Answer 2

关闭令牌化程序后，您需要一些方法来释放ItemType 。如果你之前释放它们，标记化将读入释放的内存，这是你不想做的事情。

我想你的框架应该提供一些方法来释放任何被送入HM_Put的东西。如果没有，你需要自己做。

例如（这可以通过决定在令牌和to_lower ed令牌之间保持哪个来优化：

typedef struct t_tofree {
    struct t_tofree *next;
    ItemType *item;
    char *token;   // Maybe superfluous if item->data points here...
};
t_tofree *toFree = NULL;

void mustFree(ItemType *item, char *token) {
    t_tofree *new = malloc(sizeof(t_tofree));
    new->next = toFree;
    new->item = item;
    new->token = token;
    toFree = new;
}

void freeAll() {
    while (toFree) {
        t_toFree *next = toFree->next;

        free(toFree->token); toFree->token = NULL;
        // The line below if token is *not* data and both were allocated.
        free(toFree->item->data; toFree->item->data = NULL;
        // Other cleanup on item?
        free(toFree->item); toFree->item = NULL;
        free(toFree); toFree = next;
    }
}
...

for(next_token = TKGetNextToken(tokenizer); next_token != NULL; next_token =     TKGetNextToken(tokenizer))
    {
        ItemType* item = malloc(sizeof(ItemType));
        item->data = to_lower(next_token);
        item->fileName = filename;
        item->occ = 1;
        HM_Put(hm, item);

        // Probably you can free next_token here, and only store item->data
        mustFree(item, next_token);
    }

 ...
 // Here you're REALLY REALLY sure you won't use tokens or items
 // (it's agreed that TKGetNextToken returns alloc'ed memory)
 freeAll();

解放让事情变得更糟？

2 个答案: