Question

我正在尝试创建一个简单的卡洗牌和处理模拟器。我使用向量来表示一副52张牌，每张牌由结构BitCard表示，其元素的空间是内存受位域限制。但是当构造函数尝试访问向量时，xCode会抛出BAD_ACCESS exception: Thread 1: EXC_BAD_ACCESS (code =1 address = 0x0)。我做了一些研究，发现这个异常与空指针相关联，但似乎无法弄清楚如何修复它。我的代码如下：

#include <iostream>
#include <cctype>
#include <cstdlib>
#include <vector>
#include <iomanip>
using namespace std;
struct BitCard{
    unsigned face:4;
    unsigned color:1;
    unsigned suit:2;
};
class DeckOfCards {
public:
    static const int faces = 13;
    static const int colors = 2;
    static const int numberOfCards = 52;
    DeckOfCards();
    void shuffle();
    void deal();
private:
    vector <BitCard> deck={};
};
DeckOfCards::DeckOfCards(){
    for (int i = 0; i <numberOfCards;++i){
        deck[i].face = i%faces;
        deck[i].suit = i/faces;
        deck[i].color = i/(faces*colors);
    }
}
void DeckOfCards:: shuffle(){
    for (int i = 0; i <numberOfCards;i++){
        int j = rand()%numberOfCards;
        BitCard tmp = deck[i];
        deck[i] = deck[j];
        deck[j] = tmp;
    }
}
void DeckOfCards:: deal(){
    for (int k1 = 0, k2 = k1+numberOfCards/2;k1<numberOfCards/2-1;k1++,k2++)
    {
        cout << "Color:" << setw(3) << deck[k1].color
        << " Card:" << setw(3) << deck[k1].face
        << " Suit:" << setw(3) << deck[k1].suit
        << " Color:" << setw(3) << deck[k2].color
        << " Card:" << setw(3) << deck[k2].face
        << " Card:" << setw(3) << deck[k2].suit;
    }
}



int main(int argc, const char * argv[]) {
    DeckOfCards testDeck;
    testDeck.shuffle();
    testDeck.deal();

    return 0;
}

在行

中生成异常

deck[i].face = i%faces;

我该如何解决这个问题？提前谢谢！

Answer 1

您正尝试在构造函数中访问向量deck的元素。但是当你调用构造函数时，deck向量是空的

vector <BitCard> deck={}; // <- empty deck 

DeckOfCards::DeckOfCards(){
    for (int i = 0; i <numberOfCards;++i){
        deck[i].face = i%faces; // <- At construction time, you are trying to access deck with index i. but Deck is empty!
        //...
    }
}

一种解决方案是构建对象BitCard并将其推送到vector

DeckOfCards::DeckOfCards(){
    for (int i = 0; i <numberOfCards;++i){
        BitCard myBitCard;
        myBitCard.face = i%faces;
        myBitCard.suit = i/faces;
        myBitCard.color = i/(faces*colors);
        deck.push_back(myBitCard);
    }
}

Answer 2

deck向量的大小始终为0.使用[]索引向量不会自动调整向量大小以容纳无效索引。

您可以将其初始化为正确的大小。

vector <BitCard> deck(numberOfCards);

或者在构造函数中调整它的大小。

DeckOfCards::DeckOfCards(){
    deck.resize(numberOfCards);

或者你可以在构造函数的循环中使用push_back将每张新卡添加到向量的末尾。

DeckOfCards::DeckOfCards(){
    for (int i = 0; i <numberOfCards;++i){
        BitCard card;
        card.face = i%faces;
        card.suit = i/faces;
        card.color = i/(faces*colors);
        deck.push_back( card )
    }
}

线程1：EXC_BAD_ACCESS（代码= 1地址= 0x0）

2 个答案: