Thread 1: EXC_BAD_ACCESS (code =1 address = 0x0)

Question

I am trying to create a simple card shuffling and dealing simulator. I am using a vector to represent a deck of 52 cards and each card is represented by the structure BitCard whose elements' space is memory is limited by bitfields. But when the constructor tries to access the vector, xCode throws a BAD_ACCESS exception: Thread 1: EXC_BAD_ACCESS (code =1 address = 0x0). I've done some research and found that this exception is linked with a null pointer but can't seem to figure out how to fix it. My code is as follows:

#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;
}

The exception is generated in line

deck[i].face = i%faces;

How can I fix this? Thanks in advance!

Answer 1

You are trying to access an element of your vector deck in the constructor. But when you call the constructor your deck vector is empty

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!
        //...
    }
}

One solution is to construct your object BitCard and push it to the 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

The size of your deck vector is always 0. Using [] to index a vector won't automatically resize the vector to accommodate an invalid index.

You could initialize it to the correct size.

vector <BitCard> deck(numberOfCards);

Or resize it in the constructor.

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

Or you can use push_back in the constructor's loop to add each new card to the end of the vector.

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 )
    }
}