Question

Hi I have some experience with programming but I’m not very good with pointers. I’ve been trying to debug this program I’ve been working on but it keeps giving me a segmentation fault. My code is the following:

#include <iostream>

using namespace std;

class hexagon
{
public:
    hexagon();
    ~hexagon();
    void setSide(int side, hexagon *hexpiece);
    hexagon* getSide(int side);

    void setPos(int x, int y);
    int getX();
    int getY();

    void setID(int id);
    int getID();
private:
    hexagon *side0, *side1, *side2, *side3, *side4, *side5;
    int itsid, itsx, itsy;
};

hexagon::hexagon()
{
    side0 = NULL;
    side1 = NULL;
    side2 = NULL;
    side3 = NULL;
    side4 = NULL;
    side5 = NULL;
}

hexagon::~hexagon()
{
}

void hexagon::setSide(int side, hexagon *hexpiece)
{
    switch(side)
    {
        case 0:
            side0 = hexpiece;
            break;
        case 1:
            side1 = hexpiece;
            break;
        case 2:
            side2 = hexpiece;
            break;
        case 3:
            side3 = hexpiece;
            break;
        case 4:
            side4 = hexpiece;
            break;
        case 5:
            side5 = hexpiece;
            break;
        default:
            cout << "ERROR: Invalid side passed as argument" << endl;
            break;
    }
}

hexagon* hexagon::getSide(int side)
{
    switch(side)
    {
        case 0:
            return side0;
            break;
        case 1:
            return side1;
            break;
        case 2:
            return side2;
            break;
        case 3:
            return side3;
            break;
        case 4:
            return side4;
            break;
        case 5:
            return side5;
            break;
        default:
            cout << "EROR: Invalide side passed as argument" << endl;
            cout << "Returning side0 by default" << endl;
            return side0;
            break;
    }
}

void hexagon::setPos(int x, int y)
{
    itsx = x;
    itsy = y;
}

int hexagon::getX()
{
    return itsx;
}

int hexagon::getY()
{
    return itsy;
}

void hexagon::setID(int id)
{
    itsid = id;
}

int hexagon::getID()
{
    return itsid;
}

int main()
{
    hexagon hexpieces[120];
    int tempx, tempy;
    tempx = 0;
    tempy = 0;

    for(int i = 0; i<121; i++)
    {
        if(i%11 == 0)
        {
            tempx = 7*(i/11);
            tempy = 12*(i/11);
        }
        else
        {
            tempx = tempx + 14;
        }
        cout << "Setting hexpiece" << i << " x to " << tempx << " and y to " << tempy << endl;
        hexpieces[i].setPos(tempx, tempy);
    }

    for(int i=0; i<121; i++)
    {
        cout << "Setting hexpiece" << i << " id" << endl;
        hexpieces[i].setID(i);
        for(int j = 0;j<6; j++)
        {
            cout << "Setting hexpiece" << i << " side" << j << endl;
            if(j == 0 && i > 10 && i % 11 != 10)
            {
                hexpieces[i].setSide(j,&(hexpieces[i-10]));
            }
            else if(j == 1 && i % 11 != 10)
            {
                hexpieces[i].setSide(j,&(hexpieces[i+1]));
            }
            else if(j == 2 && i < 110)
            {
                hexpieces[i].setSide(j,&(hexpieces[i+11]));
            }
            else if(j == 3 && i % 11 != 0 && i < 110)
            {
                hexpieces[i].setSide(j,&(hexpieces[i+10]));
            }
            else if(j == 4 && i % 11 != 0)
            {
                hexpieces[i].setSide(j,&(hexpieces[i-1]));
            }
            else if(j == 5 && i > 10)
            {
                hexpieces[i].setSide(j,&(hexpieces[i-11]));
            }
        }
    }

    hexagon *itr1;
    itr1 = hexpieces;   
    cout << "Hexpiece" << itr1->getID() << " side1 is connected to Hexpiece";
    itr1 = itr1->getSide(1);
    cout << itr1->getID() << endl;
    cout << "Hexpiece" << itr1->getID() << " side2 is connected to Hexpiece";
    itr1 = itr1->getSide(2);
    cout << itr1->getID() << endl;
    cout << "Hexpiece" << itr1->getID() << " side4 is connected to Hexpiece";
    itr1 = itr1->getSide(4);
    cout << itr1->getID() << endl;

    return 0;
}

My problem seems to be with the following part of the code:

int tempx, tempy;
tempx = 0;
tempy = 0;

for(int i = 0; i<121; i++)
{
    if(i%11 == 0)
    {
        tempx = 7*(i/11);
        tempy = 12*(i/11);
    }
    else
    {
        tempx = tempx + 14;
    }
    cout << "Setting hexpiece" << i << " x to " << tempx << " and y to " << tempy << endl;
    hexpieces[i].setPos(tempx, tempy);
}

When I compile the code and it includes that section it runs the program but then at the end I get a segmentation fault. However, if I comment out that section everything runs fine and there is no segmentation fault. I don’t understand how a regular integer could be causing a segmentation fault. If someone could explain what mistake I made and where I made it I would greatly appreciate it. Thanks in advance

Answer 1

hexpieces is an array of length 120, so its largest index is 119. You’re tring to access hexpieces[i] with i = 120 (that’s the last index your for loop takes on). Since you don’t “own” that memory, you get a segmentation falut.