c - 根据现有代码定义正确的结构

Question

我在 C 结构方面遇到了一些家庭作业问题……如果有人能提供帮助的话。因为我不明白。

工作代码包含这些位（这是一个游戏，蛇的头部包含方向）：

game_t *game = …;

game->snake.head->direction = …;
snake_info(game->snake)
snake_destroy(&(game->snake));

原型（我显然无法更改）：

void snake_info(snake_t const *snake);
void snake_destroy(snake_t *snake);

还有我正在尝试构建的结构。

typedef struct game {
    snake_t snake; // to match call to snake_destroy and direction assignation
    // or
    snake_t *snake; // to match call to snake_info
} game_t;

但我不能让两者同时工作。

编辑：实际struct调用snake时调用了game. 我错过了一些明显的东西还是这些原型（或调用）有问题？

编辑2：

第一个解决方案的编译器错误snake_t snake（在 中game）：

snake.c: In function ‘game_print’:
snake.c:244:5: erreur: incompatible type for argument 1 of ‘snake_info’
gamecore.c:20:6: note: expected ‘const struct snake_t *’ but argument is of type ‘snake_t’

第二种解决方案的编译器错误 ̀snake_t *snake`：

snake.c: In function ‘game_destroy’:
snake.c:205:5: attention : passing argument 1 of ‘snake_destroy’ from incompatible pointer type
gamecore.c:54:6: note: expected ‘struct snake_t *’ but argument is of type ‘struct snake_t **’

Answer 1

编译器错误说明了一切，您必须使用以下方式定义结构struct snake_t：

typedef struct game {
    struct snake_t snake;
} game_t;

你必须在给定的代码中使用snake_t snake因为。snake.head

Answer 2

您的结构不正确。您有两个同名“蛇”的成员

两者都必须在结构范围内具有唯一名称以允许合法代码

Answer 3

使用指针的位置有点混乱。随着更多的练习，使用指针对你来说会变得更自然。

此外，使用与结构名称不冲突的变量名称。

取决于您希望在代码中使用多少指针。

对现有代码的最小编辑：

typedef struct game {
    snake_t snake; // A snake_t instance is created with the game instance.. 
} game_t;

--

game_t *game = …;

game->snake.head->direction = …;

// snake_info requires a snake_t reference so pass the address of game->snake
//snake_info(game->snake);
snake_info(&(game->snake));
snake_destroy(&(game->snake));

最小的指针：

typedef struct game {
    snake_t snake; // A snake_t instance is created with the game instance.. 
} game_t;

--

// Use a game_t variable instead of a pointer
//game_t *game = …;
game_t aGame = …; // renamed variable to avoid conflicts

// change the snake.head to snake->head since the game object uses a snake_t pointer
// game->snake.head->direction = …;
aGame.snake.head->direction = …; 


// Pass the address of aGame.snake 
snake_info(&(aGame.snake));

// this line is okay since you pass the address of game->snake.
snake_destroy(&(aGame.snake));

更多地使用指针：

typedef struct game {
    snake_t *snake; // A pointer to a snake_t instance. 
} game_t;

--

// Create a game_t instance
game_t aGame = …;

// Create a snake_t instance
snake_t aSnake = ... ;


// Create a game_t pointer and assign it the address of aGame
game_t *aGamePtr = &aGame;

// Using aGamePtr, assign the snake variable in aGame the address of aSnake
aGamePtr->snake = &aSnake;


// Since the game_t object is a snake_t pointer,
// change the snake.head to snake->head 
// game->snake.head->direction = …;
aGamePtr->snake->head->direction = …; 


// this line is okay since aGamePtr->snake is a pointer.
snake_info(aGamePtr->snake);

// Since game object uses a snake_t pointer, pass aGamePtr->snake directly
// snake_destroy(&(game->snake));
snake_destroy(aGamePtr->snake);