10 replies to this topic

[lride]

I made a bomberman-like program. I keep a 2d array of Tile object in a GameMap object.
Every time the player crosses to a different tile, the new tile's onEnter() gets called and the old tile's onExit() gets called
Each tile object has std::set that stores all the entities that are on the tile. onEnter() adds the pointer to the entity to its set and onExit() erases the pointer from its set.
But my game crashes there.

[source lang="cpp"] //Check if the player moved to a different tile if(previousLoc!=currentLoc) { gameWorld->getGameMap().onEnter(currentLoc.x, currentLoc.y, this); gameWorld->getGameMap().onExit(previousLoc.x, previousLoc.y, this); } GameMap::onEnter(int x, int y, Entity * e) { tiles[y][x].onEnter(e); } GameMap::onExit(int x, int y, Entity *e) { tiles[y][x].onExit(e); } Tile::onEnter(Entity * e) { entities.insert(e); //entities is declared as std::set<Entity*> entities } Tile::onExit(Entity * e) { entities.erase(e); } [/source]


The stack trace shows up like this
> Game3.exe!std::_Tree<std::_Tset_traits<Entity *,std::less<Entity *>,std::allocator<Entity *>,0> >::_Root() Line 2139 C++
Game3.exe!std::_Tree<std::_Tset_traits<Entity *,std::less<Entity *>,std::allocator<Entity *>,0> >::_Insert_nohint<Entity * const &,std::_Nil>(bool _Leftish, Entity * const & _Val, std::_Nil _Newnode) Line 1784 C++
Game3.exe!std::_Tree<std::_Tset_traits<Entity *,std::less<Entity *>,std::allocator<Entity *>,0> >::insert(Entity * const & _Val) Line 1304 C++
Game3.exe!std::set<Entity *,std::less<Entity *>,std::allocator<Entity *> >::insert(Entity * const & _Val) Line 166 C++
Game3.exe!Tile::onEnter(Entity * e) Line 17 C++
Game3.exe!GameMap::onEnter(int x, int y, Entity * e) Line 118 C++

What can possibly cause my program to crash?

Edited by lride, 09 December 2012 - 08:34 PM.

[SiCrane]

Depending on exactly what type tiles is, some potential causes can include calling onEnter() on an uninitialized pointer, a pointer to a deleted object, a pointer to an unconstructed object, non-kosher memory use like memest() on a non-POD type, buffer overruns, accessing past the end of allocated memory, and so on.

[lride]

onEnter() merely stores the pointer in the set. It doesn't try to dereference the pointer.

[wqking]

Are you sure tiles[y][x] is valid and x, y are not out of bounds?

[lride]

Are you sure tiles[y][x] is valid and x, y are not out of bounds?

Yes, I'm using std::array in debug mode, which should result in assertion failure if x and y is out of bound

[SiCrane]

onEnter() merely stores the pointer in the set. It doesn't try to dereference the pointer.

I'm not talking about the pointer that you're trying to put in the set, I'm talking about the object that you're calling onEnter() on, either the GameMap or Tile objects.

[lride]

onEnter() merely stores the pointer in the set. It doesn't try to dereference the pointer.

I'm not talking about the pointer that you're trying to put in the set, I'm talking about the object that you're calling onEnter() on, either the GameMap or Tile objects.

anyways uninitialized pointer or pointer to deleted object, or pointer to unconstructed object aren't possible.
I'm passing the pointer with "this" pointer as you can see

[SiCrane]

1) Using this is no guarantee that the pointer is initialized.

struct Object {
  void func(void) {
    some_other_function(this);
  }
};

Object * obj; // not initialized
obj->func(); // some_other_function() will receive an uninitialized pointer.

2) I'm still not talking about the pointer that you're storing in the set, I'm talking about the object that the member function is being called on, which looks to be whatever gameWorld->getGameMap() returns.

[lride]

Ok I somewhat mitigated the crash.
Originally, all base entity had a protected pointer to the gameWorld object
But now I changed it so that I passed the gameWorld object each time in a loop.

Then I get list out of range assertion failure so at least I know what's wrong

[lride]

Now I completely solved the problem.
I have no idea why the crash occurred.
I will try to find the complete minimal example that reproduces the problem

[Trienco]

Now I completely solved the problem.
I have no idea why the crash occurred.

Not to rain on your parade, but those two statements are usually mutually exclusive.