Getter and Segmentation Fault - c++

Question

I need a bit of help on my program:
#include <iostream>
#include<conio.h>
using namespace std;
class Position {
public :
int line;
int column;
Position(int,int);
Position();
};
Position::Position(int n, int m) : line{n},column{m}{}
class Board {
private :
int** tab;
int nbline;
int nbcolumn;
public :
Board(int, int);
void setValue(Position&, int);
int getValue(Position&);
int getNbline();
int getNbcolumn();
};
class Play {
private :
// Play m_instance;
void moves(Board, Position&); // quand le joueur joue
// void moves(Board, Position); // quand l'IA joue. Mettre une énum pour direction,
bool wincondition(Board);
Play& operator=(const Play&);
public :
// static Play& Instance();
};
Board::Board(int m, int n) : tab{new int*[m]}, nbline{m}, nbcolumn{n}{
int x(0);
for (int i = 0; i < m; ++i){
tab[i] = new int[n];
for(int j = 0; j < n; ++j) {
tab[i][j] = x; x++;}}
}
void Board::setValue(Position& p, int value) { tab[p.line][p.column] = value; }
int Board::getValue(Position& p) { return tab[p.line][p.column]; }
int Board::getNbline() { return nbline; }
int Board::getNbcolumn() { return nbcolumn; }
void Play::moves(Board tab, Position& blank) {
/* int c = getch() ;
Position tmp;
if(c==0 || c==224) {c = getch();
switch(c){
case 75 : //left
if(blank.column-1>=0) {
tmp.column = blank.column;
tmp.line = blank.line;
tab.setValue(blank,tab.getValue(tmp));
blank.column++;
tab.setValue(blank, 0);
}
break;
case 72 : // haut
if(blank.line+1<=0) {
tmp.column = blank.column+1;
tmp.line = blank.line;
tab.setValue(blank,tab.getValue(tmp));
blank.column++;
tab.setValue(blank, 0);
}
break;
case 77 ://droit
if(blank.column+1<=tab.getNbcolumn()) {
tmp.column = blank.column;
tmp.line = blank.line;
tab.setValue(blank,tab.getValue(tmp));
blank.column--;
tab.setValue(blank, 0);
}
break;
case 80 : //bas
if(blank.line+1<=tab.getNbline()) {
tmp.column = blank.column+1;
tmp.line = blank.line;
tab.setValue(blank,tab.getValue(tmp));
blank.column++;
tab.setValue(blank, 0);
}
break;
default : cout << "\n ERROR " << endl; break; // erreur
}
}*/
}
int main()
{
int lines, columns;
cout << "Enter number of lines" << endl;
cin >> lines;
cout << "Enter number of columns" << endl;
cin >> columns;
Board tab(lines,columns);
Position pos(lines,columns);
Position& p = pos;
for (int i = 0; i<lines;i++)
{
for(int j = 0; j<columns;j++)
{
cout << tab.getValue(p) << " ";
if (i == lines) { cout << endl;}
}
}
return 0;
}
When I call getValue at line 139, I get a segmentation fault. Get value is defined at line 57. When executing getValue, both p.line and p.column got the right values caught at the beginning of main function.
The program got no errors, only 2 warnings because I don't use Play::moves arguments (because currently between /* */, waiting for tests). I use Code::Blocks with -Wall -Wextra -pedantic -std=c++11.
I really see no reason for a segmentation fault. Did I miss something?

Answer 1

You are calling get with a position that is set to the size of your board. Since arrays are 0 index based the size of your array is actually one past the end of the array.
const int size = 100
int arr[size]; //0, 1, 2, ... 98, 99
arr[size]; // fail arr is 0-99 and size is 100