Deleting QObjects in QMap

Mark81

I defined a struct like this:

struct MyStruct
{
    MyClass1 *class1;
    MyClass2 *class2;
};

Both classes inherits QObject. Then I have:

QMap<int, MyStruct> map;

// ...
MyStruct s;
s.class1 = new MyClass1();
s.class2 = new MyClass2();
map.insert(1, s);

Now I want to remove an item from map:

map.remove(1);

What is the right way to clean up the objects?

I don't need to explicitly do it because QObject are automatically destroyed when parent dies (map item?)
I have to call delete map[1].class1; delete map[1].class2
...

SGaist

Hi,

QMao is neither a QObject nor a parent of your MyStruct objects. It's a container.

You should add a destructor to your structure that will delete its members or use solution number 2.

Mark81

@SGaist said in Deleting QObjects in QMap:

You should add a destructor to your structure that will delete its members or use solution number 2.

The destructor will be automatically called when I remove the item from the map or I still have to manually call it?

SGaist

The destructor is called when the object is deleted. You usually never call a destructor by hand.

Mark81

@SGaist said in Deleting QObjects in QMap:

The destructor is called when the object is deleted. You usually never call a destructor by hand.

Ok, I understand this. But the question was if Qt delete the object when I remove the item from the map. Example:

map.remove(1);

if the struct has the destructor, is it called during remove()? Otherwise I still have to: delete map[1]; before remove it.

SGaist

remove deletes the object.

Note that writing a quick test would have gotten you the answer faster.

Mark81

@SGaist said in Deleting QObjects in QMap:

remove deletes the object.

Ok.

Note that writing a quick test would have gotten you the answer faster.

Well, I'm actually running a test, but I still don't understand some behaviors. So I asked to be sure at least on something...

mrjj

@Mark81
Hi
Well you want to do like

struct MyStruct {
    MyClass1 *class1 = nullptr;
    MyClass2 *class2 = nullptr;
    ~MyStruct()
    {
        delete class1;
        delete class2;
    }
};

The reason this works is that you have
QMap<int, MyStruct> map;
so when you call remove its actually deleted as its inline instance and not a pointer.
Had you
QMap<int, MyStruct *> map;

remove would only delete the pointer from the map but not called
MyStruct destructor.