Question

I want to create a SDL-based Hanoi Tower Game, but before I proceed to writing “engine”, I wanted to test my Hanoi in a console. Surprisingly, it turned out to be quite buggy.

CTower tower[3];

tower[0] = CTower(3);
tower[1] = CTower(3);
tower[2] = CTower(3);

init(&tower[0]);  //prepare first tower
tower[0].Print();

This piece of code should create 3 arrays (of size 3) and fill ’em with 0 (zeros). Then, in init(), I prepare the first tower (fill it with vaild discs). However simple may it seem, my application halts on printing and doesn’t fill the remaining arrays (with 0). What’s strange, function init() works just fine.

I would appreciate any help.

Here’s some code to check:

class CTower {
    uint16 *floors, floorsNum;

    void Init();

  public:
    (...) //definitions, probably of zero importance
};

void CTower::Init() {
  //private member, filling with zeros
  for (uint16 i = 0; i < floorsNum; i++)
    floors[i] = 0;
}
CTower::CTower() {
  //default initialiazer
  floors = NULL;
  floorsNum = 0;
}
CTower::CTower(uint16 nfloors) {
  floors = new uint16[nfloors];
  floorsNum = nfloors;
  this->Init();
}
CTower::~CTower() {
  delete[] floors;
  floorsNum = 0;
}
void CTower::Print() {
  if (floorsNum == 0) printf("EMPTY TOWER!");
  else
    for (uint16 i = 0; i < floorsNum; i++)
      printf("%d\n", floors[i]);
}
void init(CTower *tower) {
  //a friend method of CTower
  for (uint16 i = 0; i < tower->floorsNum; i++)
    tower->floors[i] = i+1;
}

My application source: https://rapidshare.com/files/2229751163/hanoi-tower.7z

Answer 1

Problem is with your initialisation and allocation of your class. It seems you have forgotten that Resource Acquisition is Initialisation.
You are facing a free corruption : you call delete[] on a not allocated attribute.

You have this constructor :

CTower::CTower() {
//default initialiazer
floors = NULL;
floorsNum = 0;
}

Which does NOT allocates memory but which is destroyed with :

CTower::~CTower() {
  delete[] floors;
  floorsNum = 0;
}

A simple way to fix your program is to allocate directly with the working constructor :

int main(void) {
  CTower tower[3] = { CTower(3), CTower(3), CTower(3) };

  init(&tower[0]);
  tower[0].Print();
  printf("\n");
  tower[1].Print();

  return 0;
}

But it would be far better to also fix your Class, either in Destructor or in Constructor part.