C：訪問函數中struct的成員

Question

我試圖在我的函數print_shoe中使用結構成員'size'，但我的for循環不運行。 但是，如果我用for循環中的int替換'c-> size'，它運行就好了

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define DECK_SIZE 52
#define NUM_FACES 13
#define NUM_SUITS 4
#define LENGTH_FACES 6
#define LENGTH_SUITS 9

typedef struct cards {
  char suits[NUM_SUITS][LENGTH_SUITS];
  char faces[NUM_FACES][NUM_FACES];
  int suit, face, card, value, size;
  int *values[NUM_FACES];
} cards;

char buf[101];
void print_shoe();
void init_decks();
int rand_int();
void shuffle();

int main(void) {

  srand( time(NULL) );

  int decks_input = 0;    
  int numberOfDecks = 1;

  do {
    printf("\nEnter number of decks to be used in the game (1-8):\n\n");
    if (fgets(buf, sizeof(buf), stdin) != NULL)
      if (sscanf (buf, "%d", &decks_input))
        numberOfDecks = decks_input;
     } while (numberOfDecks < 1 || numberOfDecks > 8);

  cards *shoe = malloc(sizeof(cards) * numberOfDecks * DECK_SIZE);
  shoe->size = numberOfDecks * DECK_SIZE;

  shuffle(shoe);
  print_shoe(shoe);

  free(shoe);

  return 0;
}

void print_shoe(cards *c) {
  int i;
  for (i = 0; i < c->size; i++) {
    printf("card #%d = %s of %s\n", i+1, c->faces[c[i].face], c->suits[c[i].suit]);
  }
}

void init_decks(cards *c) {
  int i;
  for (i = 0; i < c->size; i++) {
    c[i].card = i;
    c[i].suit = c[i].card % NUM_SUITS;
    c[i].face = c[i].card % NUM_FACES;
  }  
}

void shuffle(cards *c) {
  init_decks(c);

  int i, j;
  cards tmp;
  for (i = c->size - 1; i > 0 ; i--) {
    j = rand_int(i + 1);
    tmp = c[j];
    c[j] = c[i];
    c[i] = tmp;
  }
}

int rand_int(int n) {
  int limit = RAND_MAX - RAND_MAX % n;
  int rnd;

  do {
    rnd = rand();
     } while (rnd >= limit);
  return rnd % n;
}

編輯：問題已經廣泛更新，以回應需要進一步澄清的評論

Answer 1

在修訂后的代碼中，您有：

cards *shoe = malloc(sizeof(cards) * numberOfDecks * DECK_SIZE);
shoe->size = numberOfDecks * DECK_SIZE;

// You probably need init_decks(shoe); here!!!

shuffle(shoe);
print_shoe(shoe);

print_shoe()代碼只是打印，但是你沒有初始化malloc()以外的數據，所以你要打印垃圾。 malloc()返回的數據未初始化，必須在讀取之前進行初始化。 我打字的時候問題發生了變化; 你還沒有打電話給init_decks(shoe); 如你所願。

---

這不是它不起作用的原因 - 我不確定現在的問題是什么 - 但它幾乎值得評論。 你有：

void shuffle(cards *c) {
  init_decks(c);

  int i, j;
  cards tmp;
  for (i = c->size - 1; i > 0 ; i--) {
    j = rand_int(i + 1);
    tmp = c[j];
    c[j] = c[i];
    c[i] = tmp;
  }
}

如果您打算使用C99技術來聲明具有最小范圍的變量，那么您應該寫：

void shuffle(cards *c) {
  init_decks(c);
  for (int i = c->size - 1; i > 0; i--) {
    int j = rand_int(i + 1);
    cards tmp = c[j];
    c[j] = c[i];
    c[i] = tmp;
  }
}

（我不會錯過對init_decks()的調用， init_decks()它是這樣編寫的。）

---

正如評論中所指出的，您的cards結構相當重要。 您為每張卡分配足夠的空間來存儲它可能具有的等級和套裝。 這實際上沒有必要。

此代碼將Deck與Card分開。 它在Deck結構中使用一個靈活的陣列成員來固定卡片，這很方便。 您可能更喜歡在那里使用常規指針，在這種情況下，您需要一對內存分配和一個函數deck_free()來釋放由deck_alloc()分配的內存。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define NUM_FACES 13
#define NUM_SUITS 4
#define DECK_SIZE (NUM_FACES * NUM_SUITS)
#define LENGTH_FACES 6
#define LENGTH_SUITS 9

static const char suits[NUM_SUITS][LENGTH_SUITS] =
{
    "Clubs",
    "Diamonds",
    "Hearts",
    "Spades"
};
static const char faces[NUM_FACES][NUM_FACES] =
{
    "Ace",
    "Deuce",
    "Three",
    "Four",
    "Five",
    "Six",
    "Seven",
    "Eight",
    "Nine",
    "Ten",
    "Jack",
    "Queen",
    "King",
};

typedef struct Card
{
  int suit;
  int face;
  int card;
} Card;

typedef struct Deck
{
  int size;
  Card cards[];     // Flexible array member
} Deck;

void print_shoe(const Deck *d);
void init_decks(Deck *d);
int rand_int(int n);
void shuffle(Deck *d);
static Deck *deck_alloc(int numberOfDecks);

int main(void)
{
    srand( time(NULL) );
    int numberOfDecks = 1;

    do
    {
        char buf[101];
        printf("\nEnter number of decks to be used in the game (1-8):\n\n");
        if (fgets(buf, sizeof(buf), stdin) != NULL)
        {
            int decks_input;    
            if (sscanf (buf, "%d", &decks_input))
                numberOfDecks = decks_input;
        }
    } while (numberOfDecks < 1 || numberOfDecks > 8);

    Deck *shoe = deck_alloc(numberOfDecks);
    shuffle(shoe);
    print_shoe(shoe);
    free(shoe);

    return 0;
}

static Deck *deck_alloc(int numberOfDecks)
{
    Deck *shoe  = malloc(sizeof(Deck) + (sizeof(Card) * numberOfDecks * DECK_SIZE));
    if (shoe == 0)
    {
        fprintf(stderr, "out of memory\n");
        exit(1);
    }
    shoe->size = numberOfDecks * DECK_SIZE;
    return shoe;
}

void print_shoe(const Deck *d)
{
    for (int i = 0; i < d->size; i++)
        printf("card #%d = %s of %s\n", i+1, faces[d->cards[i].face], suits[d->cards[i].suit]);
}

void init_decks(Deck *d)
{
    for (int i = 0; i < d->size; i++)
    {
        d->cards[i].card = i;
        d->cards[i].suit = d->cards[i].card % NUM_SUITS;
        d->cards[i].face = d->cards[i].card % NUM_FACES;
    }  
}

void shuffle(Deck *d)
{
    init_decks(d);
    for (int i = d->size - 1; i > 0 ; i--)
    {
        int j = rand_int(i + 1);
        Card tmp = d->cards[j];
        d->cards[j] = d->cards[i];
        d->cards[i] = tmp;
    }
}

int rand_int(int n)
{
    int limit = RAND_MAX - RAND_MAX % n;
    int rnd;

    do
    {
        rnd = rand();
    } while (rnd >= limit);
    return rnd % n;
}

樣本輸出：

$ ./cards

Enter number of decks to be used in the game (1-8):

1
card #1 = Eight of Clubs
card #2 = Jack of Clubs
card #3 = Deuce of Diamonds
card #4 = Jack of Hearts
card #5 = Queen of Clubs
card #6 = Four of Hearts
card #7 = Six of Spades
card #8 = King of Hearts
card #9 = Five of Spades
card #10 = King of Clubs
card #11 = Deuce of Clubs
card #12 = King of Spades
card #13 = Four of Spades
card #14 = Nine of Diamonds
card #15 = Five of Hearts
card #16 = Deuce of Spades
card #17 = Ten of Clubs
card #18 = Five of Diamonds
card #19 = Ten of Spades
card #20 = Three of Spades
card #21 = Nine of Hearts
card #22 = Six of Clubs
card #23 = Ace of Clubs
card #24 = Three of Clubs
card #25 = Queen of Hearts
card #26 = Jack of Diamonds
card #27 = Nine of Clubs
card #28 = Four of Clubs
card #29 = Seven of Spades
card #30 = Ace of Diamonds
card #31 = Six of Diamonds
card #32 = Three of Hearts
card #33 = Queen of Diamonds
card #34 = Ten of Hearts
card #35 = Ten of Diamonds
card #36 = Seven of Diamonds
card #37 = Seven of Clubs
card #38 = Deuce of Hearts
card #39 = Ace of Hearts
card #40 = Jack of Spades
card #41 = Eight of Diamonds
card #42 = Eight of Spades
card #43 = Ace of Spades
card #44 = Three of Diamonds
card #45 = Queen of Spades
card #46 = Five of Clubs
card #47 = Four of Diamonds
card #48 = King of Diamonds
card #49 = Nine of Spades
card #50 = Eight of Hearts
card #51 = Six of Hearts
card #52 = Seven of Hearts
$

Answer 2

直接解決這個問題並忽略了這種方法的智慧，你的問題如下（Raymond Chen也提到過）。

  cards *shoe = malloc(sizeof(cards) * numberOfDecks * DECK_SIZE);

上面的一(numberOfDecks * DECK_SIZE)鞋子指向足夠的內存來存儲(numberOfDecks * DECK_SIZE) struct cards 。 結構，因而有成員，在這一點上都是單元化的，這意味着shoe[i].size可以是任何比特序列。

shoe-> size = numberOfDecks * DECK_SIZE;

此行僅查看第一個 struct cards並將其size設置為(numberOfDecks * DECK_SIZE) 。 其余struct cards的size成員仍然是單元化的。

在shuffle ，您對init_decks的調用初始化card ， suit和face但不是size 。 當您稍后洗牌時，具有單元size成員的卡很有可能成為第一名。

因此，根據您當前的方法，如果將此行添加到init_decks ，以下內容應該會得到您想要的init_decks 。

void init_decks(cards *c) {
      int i;
      int size = c->size;
      for (i = 0; i < c->size; i++) {
            c[i].size = size;
            c[i].card = i;
            c[i].suit = c[i].card % NUM_SUITS;
            c[i].face = c[i].card % NUM_FACES;
       }  
}

Answer 3

您已聲明指針但尚未將其初始化為指向的有效內存位置。

 ex *ex_p = malloc(sizeof(ex));
 ex_p->size = 10;