C，數組中的隨機元素變為“？” 打印到終端時為char

Question

我正在嘗試改組Card結構並將其打印到屏幕上。 隨機播放效果很好，但是在將數組打印到屏幕上時，恰好一個對象顯示為“？” 字符 每次都是不同的對象。 不改組，這是輸出：

$./shuffle
2H 3H 4H 5H 6H 7H 8H 9H TH JH QH KH AH 
2C 3C 4C 5C 6C 7C 8C 9C TC JC QC KC AC 
2D 3D 4D 5D 6D 7D 8D 9D TD JD QD KD AD 
2S 3S 4S 5S 6S 7S 8S 9S TS JS QS KS AS

這是我在改組運行程序時來自終端的一些輸出：

$./shuffle
6S 8C 7H 9H 5S 7S 4H 9C 9D AH 4S TD 4C 
JC 8D KH 5D JD 7D 7C 3D 2S 4D QH 3C TH 
AC 2H 3H 8H AS KD QS QD KC 3S 6D 9S 6H 
JH ? 5C TC QC 8S JS 6C 2D KS TS AD 2C
$./shuffle
QH TC 5H AD 3C QS 4S TH 9S 8S 5D 6C JC 
KH JH AS KS JD 7S AC 7H 6H 6D 3S 2C 3D 
5C ? 7D JS 4C QC 9C 3H 8C 2D TS 2S QD 
5S KC 4H 8D 8H KD AH TD 9D 7C 6S 2H 9H

編輯：問題是試圖訪問數組的第-1個元素會導致C訪問數組外部的數據。 謝謝！

這是我的主要代碼：

    /* Simulate a deck of cards (array of Card structures) and shuffle 
    the deck
         * Then the shuffled deck is printed to the terminal window. */
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#define DECK_SIZE (52) //52 cards in a deck

struct card { //define the structure of a card
  char suit[2]; //the suit on the card
  char value[2]; //the value of the card
};
typedef struct card Card; //define a Card type structure

Card deck[DECK_SIZE]; //a deck of cards is an array of 52 Card structures

#include "myheader.h" //myheader includes the shuffle() function for arrays of Cards

int main() {

  char suits[5] = "HCDS"; //the 4 suits
  char values[14] = "23456789TJQKA"; //the card values (T is 10)

  int j,k; //counting variables
  //fill the deck with the cards 
  for (j=0; j < 4; j++) {  //For each suit...
    for(k=0; k < 13; k++) { //and for each value...
      //Give the next card in the list that suit and value.
      deck[ ( j * 13 ) + ( k ) ].value[ 0 ] = values[ k ]; //assign the card's value
      deck[ ( j * 13 ) + ( k ) ].suit[ 0 ] = suits[ j ]; //assign the card's suit
    }
  }

  //Shuffle the deck (implementing Fisher-Yates Shuffle)
  int length = sizeof(deck)/sizeof(deck[0]);
  //shuffle function is found in "myheader.h"
  shuffle( &deck[0], length ); //pass a pointer to the first position of the deck

  //Print the deck to the screen (assuming 52 card deck)
  for (j=0; j < 4; j++) { //for each suit...
    for (k=0; k < 13; k++) { //for each value...
      //print the card
      printf("%s%s ", deck[ ( j * 13 ) + ( k ) ].value, deck[ ( j * 13 ) + ( k )].suit); 
    }
    //print a new line so the rows are organized into 4 rows of 13 cards each.
    printf("\n");
  }
}
//End of program.

這是我在其中定義隨機播放功能的標頭：

//Requires math.h
//Requires stdlib.h
//Requires time.h

void shuffle(Card deck[], int length) { //takes an pointer to the array of type Card
  //This shuffle function implements the Fisher-Yates shuffle algorithm.
  printf("Length is: %i\n",length);
  int element;
  Card temp; //a place to temporarily store cards while shuffling them.
  srand(time(NULL)); //seed the random number generator with the current time.

  while (length) {
    //While there are things to shuffle
    //Pick a remaining element from the un-randomized elements
    element = rand() % (length); 
    length--; //decrease the "length" of the part of the array that is still unshuffled

    //Swap the element with the last element in the list.
    temp = deck[length]; //temporarily store the end object in the last slot
    deck[length] = deck[element-1];
    //place the selected element in the 'vacated' last slot
    deck[element-1] = temp;
    //put the temporarily stored object in place of the element 
  }
}
//There is a bug where one of the elements in the array gets changed to a ?

我懷疑shuffle函數中存儲在temp結構中的結構之一在通過傳遞時被弄亂了，但是我不確定為什么只有一個對象被弄亂了，大概是因為在隨機播放循環中，將數組置於某一點的溫度下。 我是C語言的初學者，我知道足夠的東西來編寫東西，但是對於調試這種奇怪行為的實際操作還不夠了解。 如果有人知道有關此“？”的任何信息 字符來自或為什么將其插入數組會很有幫助。 謝謝！

Answer 1

element = rand() % (length);

給您一個介於0和length-1之間的值。

deck[length] = deck[element-1];

可以在元素為0時訪問數組外部