Segfault/ "Vector is not dereferencable" on std::vector push_back - c++

Question

I have some C++ code dealing with a card game and it's segfaulting and I can't figure out why. I tried running it in MSVS 2012 to get a more clear error and it threw a "Vector is not dereferencable." I tried doing some research but I'm lost on where the error is coming from. I'm guessing the bug isn't in the push_back but rather somewhere else as the problem line works most of the time. The error occurs in Table::hit(). After looking through the code I think the bug may possibly lie in Hand::split() but I am not sure and I am even less sure how to fix it. Thanks!
class Hand
{
public:
std::vector<Card> hand;
bool active, doubled, isBlackjack, busted;
Hand() : active(true), doubled(false), isBlackjack(false), busted(false) { }
Hand(const Hand& _hand);
void removeCard(Card card) { hand.erase( hand.begin() ); }
Card split();
void clear();
int cards() const { return hand.size(); }
int getHandValue() const;
Card at(int pos) { return hand[pos]; }
friend std::ostream& operator<< (std::ostream& out, const Hand& hand);
friend std::ostream& operator<< (std::ostream& out, const std::vector<Hand>& hands);
};
Hand::Hand(const Hand& _hand)
: hand(_hand.hand), active(_hand.active), doubled(_hand.doubled), isBlackjack(_hand.isBlackjack), busted(_hand.busted)
{ }
Card Hand::split()
{ //COULD THE BELOW CODE BE CAUSING ISSUES?
Card card = hand[0];
hand.erase( hand.begin() );
return card;
}
void Hand::clear()
{
active = true;
hand.clear();
}
int Hand::getHandValue() const
{
int value(0), aces(0);
for(std::vector<Card>::const_iterator it = hand.cbegin(); it != hand.cend(); ++it)
{
value += getCardValue(it->getRank());
if(it->getRank() == ACE)
++aces;
}
while(aces > 0 && value > 21)
{
value -= 10;
--aces;
}
return value;
}
std::ostream& operator<< (std::ostream& out, const Hand& hand)
{
for(std::vector<Card>::const_iterator it = hand.hand.begin(); it != hand.hand.end(); ++it)
{
out << *it << " ";
}
out << hand.getHandValue();
return out;
}
std::ostream& operator<< (std::ostream& out, const std::vector<Hand>& hands)
{
for(std::vector<Hand>::const_iterator it = hands.begin(); it != hands.end(); ++it)
{
out << *it << " ";
}
return out;
}
class Table
{
protected:
Shoe shoe;
Strategy strat;
Hand dealer;
std::vector< Hand > player;
double balance, blackjackPayoff;
bool hitSoft17;
void deal();
void hit(int split=0);
void split(int split=0);
double stand();
Action getUserAction();
bool isCurrentGame();
public:
Table(int decks, int _balance);
double bet;
void play();
void print();
void simulate(std::string fileName, int hands);
};
Table::Table(int decks, int _balance)
: shoe(decks), balance(_balance), blackjackPayoff(1.5), hitSoft17(true), bet(10)
{}
bool Table::isCurrentGame()
{
for(std::vector<Hand>::iterator it = player.begin(); it != player.end(); ++it)
{
if(it->active)
return true;
}
return false;
}
void Table::deal()
{
dealer.clear();
player.clear();
dealer.addCard( shoe.pullCard(true) );
dealer.addCard( shoe.pullCard() );
player.push_back(Hand());
player[0].addCard( shoe.pullCard() );
player[0].addCard( shoe.pullCard() );
if(player[0].getHandValue() == 21 && dealer.getHandValue() == 21)
{
player[0].active = false;
}
else if(player[0].getHandValue() == 21)
{
player[0].active = false;
}
else if(dealer.getHandValue() == 21)
{
player[0].active = false;
}
}
void Table::hit(int split)
{
player[split].hand.push_back( shoe.pullCard() ); //SEGFAULT HERE
if(player[split].getHandValue() > 21)
{
player[split].active = false;
}
}
void Table::split(int split)
{
player.push_back(Hand());
player[player.size() - 1].hand.push_back( player[split].split() );
player[split].hand.push_back( shoe.pullCard() );
player[player.size() - 1].hand.push_back( shoe.pullCard() );
if(player[split].getHandValue() == 21)
{
player[split].active = false;
}
else if(player[player.size() - 1].getHandValue() == 21)
{
player[player.size() - 1].active = false;
}
}
double Table::stand()
{
double winnings(0.0);
bool allNats(true);
//dealer.push_back( shoe.pullCard() );
for(std::vector<Hand>::iterator it = player.begin(); it != player.end(); ++it)
{
if(it->cards() == 2 && it->getHandValue() == 21)
{
winnings += bet * blackjackPayoff;
it->isBlackjack = true;
}
else
{
allNats = false;
if(it->getHandValue() > 21)
it->busted = true;
}
}
if(!allNats)
{
while(dealer.getHandValue() <= 17)
{
if(dealer.getHandValue() == 17)
{
//dealer has 17 and doesnt hit soft 17s so hes not going to draw anymore cards
if( !hitSoft17 || dealer.cards() != 2 || !(dealer.hand.at(0) == ACE || dealer.hand.at(1) == ACE) )
break;
}
dealer.addCard( shoe.pullCard() );
}
}
for(std::vector<Hand>::iterator it = player.begin(); it != player.end(); ++it)
{
if(!it->isBlackjack)
{
if(it->busted)
{
if(it->doubled)
winnings -= 2.0 * bet;
else
winnings -= bet;
}
else if(dealer.getHandValue() > 21 || dealer.getHandValue() < it->getHandValue())
{
if(it->doubled)
winnings += 2.0 * bet;
else
winnings += bet;
}
else if(dealer.getHandValue() > it->getHandValue())
{
if(it->doubled)
winnings -= 2.0 * bet;
else
winnings -= bet;
}
}
}
//only other scenario is a push which we dont do anythign for
return winnings;
}
void Table::simulate(std::string fileName, int hands)
{
int i(0), countHL;
double trueCountHL;
std::ofstream ofs(fileName);
Action action;
while(i < hands)
{
deal();
VisibleCards vc(player[0].at(0), player[0].at(1), dealer.at(0));
while(isCurrentGame())
{
int j(0), q(1);
countHL = shoe.getCountHL();
trueCountHL = shoe.getTrueCountHL();
for(int l = 0; l < q; ++l)
{
while(player[l].active)
{
if(player[l].cards() == 2)
action = getBasicStrategy(player[l].getHandValue(), dealer.at(0).getCardValue(),
player[l].at(0).getCardValue(), player[l].at(1).getCardValue());
else
action = getBasicStrategy(player[l].getHandValue(), dealer.at(0).getCardValue());
switch(action)
{
case HIT:
hit(j);
break;
case DOUBLE:
hit(j);
if(player[l].cards() == 3)
{
player[l].doubled = true;
player[l].active = false;
}
break;
case SPLIT:
if(player.size() <= 4)
{
split(j);
++q;
}
else
hit(j);
break;
case STAND:
player[l].active = false;
break;
}
++j;
}
}
}
double winnings = stand();
balance += winnings;
ofs << std::endl << std::fixed << vc << "," << winnings << "," << std::setprecision(2) << trueCountHL
<< "," << balance << "," << std::setprecision(0) << countHL << "," << shoe.getRemainingDecks();
ofs << std::endl << 1;
//BlackjackData bjd(winnings, balance, shoe.getTrueCountHL(), shoe.getCountHL(), HIT);
//strat.addData(vc, bjd);
++i;
}
strat.print(fileName);
}

Answer 1

Looks like you're trying to get the first card from hand with hand[0] and hand.erase(hand.begin()) without first checking that there IS a first card. If hand is empty (as is the case with a newly created Hand from the constructor), this causes undefined behavior, which may well manifest as a crash at some later time.

Answer 2

I stared at this for a day and couldn't figure it out, stepped out and realize I had an old variable "j" that I was using to access the vector instead of "l" when I was calling the "hit" function.... Thanks everyone for the help.