Proper QList usage

[smick]

Hi

I am using Qlist of objects of type MyObj in an instance of class AClass

Should I store the as a list of pointers to MyObj

QList <MyObj*> mylist;

QList <MyObj*> mylist;

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The function to add items to my list is as follows

void AClass::addToList(const QList <MyObj> &items)
{
    foreach(MyObj m, items)
    {
        MyObj mm = new MyObj(m);
        mylist.append(mm);
    }
}

void AClass::addToList(const QList <MyObj> &items)
{
    foreach(MyObj m, items)
    {
        MyObj mm = new MyObj(m);
        mylist.append(mm);
    }
}

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OR a list of MyObj instances and i add to the list as follows

QList <MyObj> mylist;

QList <MyObj> mylist;

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void AClass::addToList(const QList <MyObj> &items)
{
    mylist.append(items);
}

void AClass::addToList(const QList <MyObj> &items)
{
    mylist.append(items);
}

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Which of the two cases above is the best way?

I have a problem removing items from the list as the MyObj class does not have a comparison operator

For example, I have a function to remove items from the list

void AClass::removeFromList(const QList <MyObj> &items)
{
     foreach(MyObj m, items)
     {
        /*
        what do I put in here if I want to remove 'items' from mylist
        */
     }
}

void AClass::removeFromList(const QList <MyObj> &items)
{
     foreach(MyObj m, items)
     {
        /*
        what do I put in here if I want to remove 'items' from mylist
        */
     }
}

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Regards

[Zlatomir]

This page will give you an overview of QList.

Now my little advice: use QList (or other containers) of pointers mainly in two cases:
1) if you have some classes that can't be copied (eg QObject derived classes)
or,
2) if you have "big" objects that are "hard" to copy.

And when using container<sometype*> you can think of using container<smart_pointer<sometype> > instead, Qt has some smart_pointers, like QSharedPointer.

[smick]

Thanks for the advice Zlatomir.

MyObj is not so big so I have not use a QList of pointers, however how can I search the list (and replace/remove items) if MyObj does not have a comparison operator defined ?

[Zlatomir]

You can use list.removeAt(position);
But, if you need to test for equality (like to find the position ) or compare objects of your type you need to overload the operators for your type.
Or use some algorithms like std::find_if (that takes predicate that does the comparison) or code your own algorithms that take a predicate.

One more thing, as i see you talk about removal from QList - i have to say QList is more similar to std::vector than std::list (read the link in my previous post) - in short: QList is not a linked-list, Qt has QLinkedList class that implements a linked-list data-structure.