Why is there a Segmentation Fault from this vector code? - c++

Question

When I execute this code in Code::Blocks I get a segmentation fault. Why? I've used debug and haven't found why. Any help is useful.
The debugger showed it was from the vector push_back method, but specifically on the "this" pointer used in the copy constructor.
#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <cmath>
const int MAX_COL = 7, MAX_ROW = 6;
const int NOPLAYER = 0, PLAYER1 = 1, PLAYER2 = 2;
const int NOTHING = 123;
int movesBeingStored = 0;
int movesCreated = 0;
class Move{
public:
Move() : row(-1), col(-1), plr(-1) {
//std::cout << "Placed #" << col << "," << row << std::endl;
++movesBeingStored;
++movesCreated;
std::cout << "+Now " << movesBeingStored << " move(s), Created " << movesCreated << std::endl;
};
Move(int r, int c, int p) : row(r), col(c), plr(p) {
++movesBeingStored;
++movesCreated;
std::cout << "+Now " << movesBeingStored << " move(s), Created " << movesCreated << std::endl;
};
~Move() {
--movesBeingStored;
std::cout << "-Now " << movesBeingStored << " move(s)" << std::endl;
};
int getRow() const { return row; }
int getCol() const { return col; }
int getPlayer() const { return plr; }
Move(const Move* other) {
++movesBeingStored;
++movesCreated;
std::cout << "+Now " << movesBeingStored << " move(s), Created " << movesCreated << std::endl;
col = other->getCol();
row = other->getRow();
plr = other->getPlayer();
}
Move(const Move& other) {
++movesBeingStored;
++movesCreated;
std::cout << "+Now " << movesBeingStored << " move(s), Created " << movesCreated << std::endl;
col = other.getCol(); //This line causes a segment fault
row = other.getRow();
plr = other.getPlayer();
}
bool operator== (const Move& other) const {
return (&other == this);
}
private:
int row, col, plr;
};
int board[MAX_COL * MAX_ROW];
std::vector<Move> moves;
bool isFull[MAX_COL];
int tops[MAX_COL];
int currentPlayer = PLAYER1;
int checkedCollumns = 0;
void randomize( void ) { srand(time(NULL)); }
void startBoard( void );
void placeMove(int col, int player);
void popMove();
int checkwin(int curPlayer);
int checkMove(int depth, int& bestCol, int curP, int checkP);
int randomInt(int min, int max);
void printMoves( void );
int main()
{
startBoard();
randomize();
int col = -1;
int pts = checkMove(2, col, PLAYER1, PLAYER1);
if(col == -1) {
std::cout << "No best move" << std::endl;
} else {
std::cout << "Best move: Col " << col << std::endl;
if(pts == NOTHING) {
std::cout << "Nothing happens" << std::endl;
} else {
std::cout << "Gives " << pts << " points" << std::endl;
}
}
}
void startBoard( void ) {
for(int i = 0; i < MAX_COL; ++i) {
isFull[i] = false;
tops[i] = 0;
}
for(int p = 0; p < MAX_COL * MAX_ROW; ++p) {
board[p] = NOPLAYER;
}
}
void placeMove(int col, int player) {
if(col < 0 || col >= MAX_COL)
return;
if(isFull[col])
return;
if(player != PLAYER1 && player != PLAYER2)
player = PLAYER1;
moves.push_back(Move(col, tops[col], player));
board[col + tops[col] * MAX_COL] = player;
++tops[col];
isFull[col] = (tops[col] == MAX_ROW);
}
void popMove() {
if(moves.empty())
return;
Move move = moves.back();
moves.pop_back();
int col = move.getCol(), row = move.getRow();
board[col + row * MAX_COL] = NOPLAYER;
tops[col] = row;
isFull[col] = (tops[col] == MAX_ROW);
}
int checkwin(int curPlayer) {
if(randomInt(0,5) != 1)
return NOTHING;
return randomInt(0,4);
}
int checkMove(int depth, int& bestCol, int curP, int checkP) {
int pts = NOTHING, col = -1, p = NOTHING, c = -1;
if(depth <= 0) {
if(moves.empty()) {
bestCol = -1;
return NOTHING;
}
Move move = moves.back();
bestCol = move.getCol();
pts = checkwin((move.getPlayer());
if(move.getPlayer() != checkP && pts != NOTHING)
pts = -pts;
return pts;
}
for(int i = 0; i < MAX_COL; ++i) {
std::cout << "C: " << checkedCollumns;
std::cout << "\tD: " << depth;
std::cout << "\tM: " << moves.size();
std::cout << std::endl;
if(isFull[i])
continue;
++checkedCollumns;
placeMove(i, curP);
p = checkMove(depth - 1, c, ((curP == PLAYER1)?PLAYER2:PLAYER1), checkP);
popMove();
if(p != NOTHING && checkP != curP)
p = -p;
if(col == -1) {
col = i;
pts = p;
continue;
}
if(pts == NOTHING && p != NOTHING && p >= 0) {
col = i;
pts = p;
continue;
}
if(pts != NOTHING && p != NOTHING && p > pts) {
col = i;
pts = p;
}
}
bestCol = col;
return pts;
}
int randomInt(int min, int max) {
double per = (double)(rand() % RAND_MAX) / RAND_MAX;
return min + (max - min) * per;
}
void printMoves( void ) {
std::cout << "M:";
if(moves.empty()) {
std::cout << " --\t" << moves.size();
return;
}
Move m;
for(unsigned int i = 0; i < moves.size(); ++i) {
m = moves.at(i);
std::cout << " {" << m.getCol() << "," << m.getRow() << "}";
}
std::cout << "\t" << moves.size();
}

Answer 1

A very trivial error, manifesting in a very obscure way. The segment fault is caused by the vector trying to construct an object at an invalid location. Why? Because of the following line in void popMove():
board[col + row * MAX_COL] = NOPLAYER;
This line has a buffer overflow caused by invalid coordinates (0, 6), which overwrites the internal memory pointer in moves. That's the problem, the solution is up to you.