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Heap-leaks and polymorphic containers [message #15857]

Mon, 12 May 2008 17:41

mrjt
Messages: 705
Registered: March 2007
Location: London

Contributor

It is my understanding that the following code should execute without any memory leaks:

struct Item {
	String name;	
};

struct Collection : public Item
{
	Array<Item> items;
};

GUI_APP_MAIN
{
        // Example 1
	Array<Item> array;
	array.Create<Collection>().items.Add();

        // Example 2
	Collection *col = new Collection();
	col->items.Add();
	Item *item = (Item *)col;
	delete item;
}

But for some reason the destructor for 'items' isn't getting called. Adding a virtual destructor to force clearance just causes a crash in MemoryFreeDebug.

Is something broken or am I just missing something obvious?

[Updated on: Mon, 12 May 2008 17:49]

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Re: Heap-leaks and polymorphic containers [message #15858 is a reply to message #15857]

Mon, 12 May 2008 19:05

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

mrjt wrote on Mon, 12 May 2008 11:41

It is my understanding that the following code should execute without any memory leaks:

struct Item {
	String name;	
};

struct Collection : public Item
{
	Array<Item> items;
};

GUI_APP_MAIN
{
        // Example 1
	Array<Item> array;
	array.Create<Collection>().items.Add();

        // Example 2
	Collection *col = new Collection();
	col->items.Add();
	Item *item = (Item *)col;
	delete item;
}

Well, virtual destructor is absolutely required here.

The crash in MemoryFreeDebug... well, who knows, I would say it has another reason.

Mirek

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Re: Heap-leaks and polymorphic containers [message #15864 is a reply to message #15858]

Tue, 13 May 2008 15:46

mrjt
Messages: 705
Registered: March 2007
Location: London

Contributor

luzr wrote on Mon, 12 May 2008 18:05

Well, virtual destructor is absolutely required here.

Hmm. I understand why this works (the implicit destructor isn't virtual):

struct Item : public Moveable<Item> {
	String name;
	
	virtual ~Item() { }	
};

struct Collection : public Item
{
	Array<Item> items;
};

GUI_APP_MAIN
{
	Collection *col = new Collection();
	col->items.Add();
	Item *item = (Item *)col;
	delete item;
}

But what baffles me is why this works with Vector, but not Array (the Array's destructor doesn't get called but the Vector one does).

struct Item : public Moveable<Item> {
	String name;	
};

struct Collection : public Item
{
	Vector<Item> items; // Heap leak if changed to Array
};

GUI_APP_MAIN
{
	Collection *col = new Collection();
	col->items.Add();
	Item *item = (Item *)col;
	delete item;
}