Constructors and scope issue

Algar · #1 02-Nov-2007, 16:19

Ok, well theres a lot of code to this problem so ill describe as best I can instead of showing 10 pages.

I have a container class MapCell
Inside that class there are pointers to 2 other classes CharBase and TerBase. All 3 classes are derived from CRect (doubt thats relevant)

I am trying to manage memory completely from within the container class.
Heres the members from MapCell that might be relevant to the problem:
(It might be better to skip this block of code and look at the next before coming back)

CPP / C++ / C Code:

TerBase* terrain;		//pointer to dynamic layer 1
CharBase* character;	//pointer to dynamic layer 2

MapCell::MapCell() { //default constructor
	terrain = new TerBase();
	character = new CharBase();
}

MapCell::MapCell(CPoint topLeft, CPoint botRight) { //Rect constructor
	terrain = new TerBase();
	character = new CharBase();
	setSizePos(topLeft, botRight);
}

MapCell::MapCell(const MapCell & mapCell) { //copy constructor
	terrain = new TerBase(mapCell.getTerrain());
	character = new CharBase(mapCell.getCharacter());
}

MapCell::~MapCell() { //destructor
	delete character;
	delete terrain;
}

CharBase MapCell::getCharacter() const {	//deep copy		
	return CharBase(*character);
}

TerBase MapCell::getTerrain() const { 	//deep copy
	return TerBase(*terrain);
}

So thats generally how the copying / construction / destruction is handled

but now when I go to populate a 2d vector of these MapCells I have some big problems.

CPP / C++ / C Code:

	const int SIZE = 30;
	map.resize(10);
	for (UINT i=0; i<map.size(); i++)
		map[i].resize(10);

	for (UINT i=0; i<map.size(); i++) {
		for (UINT j=0; j<map[i].size(); j++) {
			MapCell cell;
			CPoint tl(i*SIZE, j*SIZE);
			CPoint br(tl.x+SIZE, tl.y+SIZE);
			cell.setSizePos(tl,br);
			map[i][j] = cell;
		}
	}

Its probably emmediately apparent, but basically the cell is created inside the block, then the destructor is called after basically deleting both pointers.

I am not sure if I am just not populating the vector properly, or my construction / copy / destruction is wrong.

Any help appreciated, thanks.

Algar · #2 02-Nov-2007, 16:57

Ok so I changed the way I am populating the vector.

CPP / C++ / C Code:

	const int SIZE = 30;
	vector<MapCell> x(10, MapCell());
	for (int i=0; i<10; i++)
		map.push_back(x);

	for (UINT i=0; i<10; i++) {
		for (UINT j=0; j<10; j++) {
			map[i][j].setSizePos(CPoint(i*SIZE,j*SIZE), CPoint((i+1)*SIZE,(j+1)*SIZE));
		}
	}

And now it appears to be working fine.

Is it that pushback makes a deep copy , but = is shallow ?

Kimmo · #3 03-Nov-2007, 01:29

Quote:

Originally Posted by Algar

Is it that pushback makes a deep copy , but = is shallow ?

They both do whatever the class copy constructor and assignment operator do. Since you don't have an overloaded assignment operator, a member-wise copy is what you get.

I didn't look at your code, though, but if you tested it's working now, then the assignment operator is most likely the cause.

Algar · #4 03-Nov-2007, 01:52

Ok, thanks for the info !

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