在 malloc() 之后使用 memset() 会导致断言

Question

我有一个这样的结构：

struct state {
    bool isfinal;
    bool *isfull;
    char **board;
};

isfull

是一个数组，

board

是一个二维数组。

我可以使用此函数为数组分配内存：

struct state new_state(struct state state)
{
    int i;
    struct state new_state = {};
    new_state.isfull = (bool *) malloc(BOARD_WIDTH *sizeof (bool));
    new_state.board = (char **) malloc(BOARD_HIGHT *sizeof (char *));
    for (i = 0; i < BOARD_HIGHT; ++i)
        new_state.board[i] = (char *) malloc(BOARD_WIDTH *sizeof (char));
    if (state.board) {
        memcpy(new_state.isfull, state.isfull, BOARD_WIDTH * sizeof (bool));
        memcpy(new_state.board, state.board, BOARD_HIGHT + BOARD_HIGHT * BOARD_WIDTH);
    } else {
        getchar();
        memset(new_state.isfull, 0, BOARD_WIDTH * sizeof (bool));
        for (i = 0; i < BOARD_HIGHT; ++i)
            memset(new_state.board[i], 0, BOARD_HIGHT * sizeof (char *));
    }
    return new_state;
}

第一次使用 0 调用该函数，else 块将被执行。 这会产生一个断言。 同样，在断言的情况下，函数会执行到 return 语句，然后程序才会中断。

我已经通过使用 calloc() 解决了这个问题。 这有效：

struct state new_state(struct state state)
{
    int i;
    struct state new_state = {};
    new_state.isfull = (bool *) calloc(BOARD_WIDTH ,sizeof (bool));
    new_state.board = (char **) calloc(BOARD_HIGHT ,sizeof (char *));
    for (i = 0; i < BOARD_HIGHT; ++i)
        new_state.board[i] = (char *) calloc(BOARD_WIDTH ,sizeof (char));
    if (state.board) {
        memcpy(new_state.isfull, state.isfull, BOARD_WIDTH * sizeof (bool));
        memcpy(new_state.board, state.board, BOARD_HIGHT + BOARD_HIGHT * BOARD_WIDTH);
    } else {
        // memset(new_state.isfull, 0, BOARD_WIDTH * sizeof (bool));
        // for (i = 0; i < BOARD_HIGHT; ++i)
        //     memset(new_state.board[i], 0, BOARD_HIGHT * sizeof (char *));
    }
    return new_state;
}

有趣的是，使用 getchar() 函数作为延迟形式也有效！ 像这样：

struct state new_state(struct state state)
{
    int i;
    struct state new_state = {};
    new_state.isfull = (bool *) malloc(BOARD_WIDTH *sizeof (bool));
    new_state.board = (char **) malloc(BOARD_HIGHT *sizeof (char *));
    for (i = 0; i < BOARD_HIGHT; ++i)
        new_state.board[i] = (char *) malloc(BOARD_WIDTH *sizeof (char));
    if (state.board) {
        memcpy(new_state.isfull, state.isfull, BOARD_WIDTH * sizeof (bool));
        memcpy(new_state.board, state.board, BOARD_HIGHT + BOARD_HIGHT * BOARD_WIDTH);
    } else {
        getchar();
        memset(new_state.isfull, 0, BOARD_WIDTH * sizeof (bool));
        for (i = 0; i < BOARD_HIGHT; ++i)
            memset(new_state.board[i], 0, BOARD_HIGHT * sizeof (char *));
    }
    return new_state;
}

搜索互联网，我发现在 malloc() 之后使用 memset() 是一种常见的做法。 所以第一个问题：为什么我的函数的第一个版本不起作用？ 第二：为什么使用 getchar() 使它起作用？

Answer 1

看起来像是一个错字，你使用的是：

memset(new_state.board[i], 0, BOARD_HIGHT * sizeof (char *));

而不是：

memset(new_state.board[i], 0, BOARD_WIDTH * sizeof (char *));

如果

BOARD_HIGHT != BOARD_WIDTH

那么你可以让元素未初始化（并且具有不确定的值），否则你将超出界限并具有明确的未定义行为。

我假设您复制粘贴了

memset

调用，但忘记更改此设置。