Why can't I call append on this QList?

QList<Artist> * DataManagement::create_and_get_artists(){

    QList<Artist> *artists = new QList<Artist>;

    for(int i; i < m_allSongs->rowCount(); i  ){
        Artist *artist = new Artist();
        artist->setName(m_allSongs->record(i).value("artistName").toString());
        artists->append(artist);

    }

    return artists;
}

Screenshot of error

Error message: "no matching member function for call to 'append'".

CodePudding user response：

You can call append on a QList type, but only with an appropriate parameter.

In the code, artist is a pointer to the Artist type, while the QList is a list of Artist types.

In the screenshot, no parameter is given at all.

CodePudding user response：

Let's look at the documentation (always check the documentation first!).

There are two overloads of append():

void QList::append(const T &value)

and

void QList::append(const QList<T> &value)

So you can append a value or a list of values.

In your code on the screenshot, you call artists->append();. That is, you are not providing any argument. No member function append() with zero arguments exist.

Managing Object Lifetimes

Remember that you are responsible for managing memory in C ! You have a QList<Artist>, i.e., a list of actual objects. Yet you create an Artist using new. Now you have a pointer to a heap allocated object.

Calling append(obj) will actually copy the object, i.e., call the copy constructor! You are then responsible to free the temporary object you created!

Alternatively, you could use a QList<Artist*>, i.e., a list of pointers. But I think this is the worst option.

You could also construct a temporary object on the stack and then copy it:

Artist artist{};
artist.setName("bla");
artists->append(artist);

But it would be much better - if you use Qt6 - to just construct the object directly into the list, using emplaceBack(). (You need the matching constructor, of course).