如何在C的结构内索引指针

Question

How do I index a pointer of variable length inside a struct? My situation is as follows:

I am working on a card simulation game and I am trying to point the playing cards to the same location as a particular card in the deck. However, I am getting the error, "error: incompatible types when assigning to type 'Card' from type 'struct Card *'".

As I understand it, this is occurring because the way that I'm accessing the Card inside the struct is incorrect. That is, I believe I set up the Hand type properly, but I'm not indexing the cards inside of it correctly to assign the pointers to the same location as the deck's cards.

What I think makes this question unique is that I'm trying to assign each pointer in the struct Hand to a location in memory. When I try to use the brackets to index playingCards the compiler dereferences playingCards and accesses the underlying Card data. What I'd like to do is loop over the hand size (5) and deal a card to each player by pointing the player's card pointer to the card I just dequeued. Then, I put the card at the back of the deck.

My data abstractions are as follows and my code to assign the pointer is as follows:

typedef struct card_{
    char* rank;
    char* suit;
} Card;

typedef struct deck_{
    Queue cardDeck;
}Deck;

typedef struct hand_{
    Card *playingCards;
}Hand;

typedef struct player_{
    Hand hand;
    int bank_roll;
}Player;

typedef struct table_{
    Player player[NUM_PLAYERS];
}Table;

Pointer assignment:

cTable->player[playerIndex].hand.playingCards = cardRemoved;

However, this only assigns cardRemoved to the first Card pointer. What I'd like to do is something like:

cTable->player[playerIndex].hand.playingCards[cardIndex] = cardRemoved;

But then when I do that it dereferences playingCards as mentioned above, and throws the error error: incompatible types when assigning to type 'Card' from type 'struct Card *'

Please let me know what I'm doing wrong here. Any help would be greatly appreciated!

Answer 1

If I'm understanding correctly, what you want is for playingCards to be an array of pointers.

If you know the size of the array you can just make it a static array like you did for the Table struct, as follows:

typedef struct hand_{
    Card *playingCards[NUM_CARDS_IN_HAND];
}Hand;

this makes playingCards an array of Card *, and the code you mentioned above

cTable->player[playerIndex].hand.playingCards[cardIndex] = cardRemoved;

would work.

If you don't have a limit on the size of playingCards, you can make playingCards a Card **, as follows:

typedef struct hand_{
    Card **playingCards;
}Hand;

and then dynamically allocate the space as you add and remove cards to it.

In this case, you know that the max number of cards in a hand will be 5, so I think the first example would be sufficient.