Destructor array of object

JohanSolo

Since your buttons have a parent, you don't have to delete them.
Your array is a regular one (unless you implemented it differently from your 1st snippet) so DON'T delete it.

goetz

A member of a class (be it public, protected or private doesn't matter at all) can be allocated on the stack or on the heap.

@
class blurb {
public:
blurb() {
radioHeap = new QRadioButton *[8];
}

~blurb() {
    delete[] radioHeap;
    // never ever call this:
    // delete[] radioStack;
}

private:
// an array of size 8 allocated on the stack
// DO NOT call delete[] in the destructor
QRadioButton *radioStack[8];

// an array of unknown size allocated on the heap
// you have to allocate it somewhere (eg. constructor)
// and have to delete it somewhere (eg. destructor)
QRadioButton *radioHeap[];

};
@

So, if you defined it like in the first post, Johan is right and you do a double deletion.

BTW: Why don't you use one of the nice container classes of Qt? One should avoid raw arrays unless absolutely needed. They're cumbersome to use.

stukdev

Ooh i don't know the difference from
@
QRadioButton *radioStack[8];
//and
QRadioButton *radioHeap[];
@
Thank's.

[quote author="Volker" date="1329155246"]
BTW: Why don't you use one of the nice container classes of Qt? One should avoid raw arrays unless absolutely needed. They're cumbersome to use.[/quote]

What type of container class can i use here?

KA51O

Here's an overview for all of "Qt's container classes":http://developer.qt.nokia.com/doc/qt-4.8/containers.html. Some are optimized for quick access, some for quick insertion...

stukdev

So i can get this:

@
//private definition class
private:
QList<QRadioButton*>radio;

//costructor class
for(quint8 a=0;a<8;a++)
radio << new QRadioButton(parentWidget);
@

This is more efficient then create manually array and i haven't to delete anything in descructor. Right?

KA51O

correct

goetz

[quote author="stuk" date="1329208992"]So i can get this:

@
//private definition class
private:
QList<QRadioButton*>radio;

//costructor class
for(quint8 a=0;a<8;a++)
radio << new QRadioButton(parentWidget);
@

This is more efficient then create manually array and i haven't to delete anything in descructor. Right?[/quote]

NO

Regarding efficiency:
Using a container instead of a plain old array is always a bit slower, but for the common use cases this plain doesn't matter because no one ever notices. And advantages, like consistent API and safety, prevail massively most times.

Regarding deletion:
The container classes, if filled with pointers, never call delete on that pointers once they are removed from the list or in case the list is emptied or destroyed. You must call delete yourself. In case of the Qt container classes there is a nice helper function:

@
qDeleteAll(radio);
@

lgeyer

[quote author="Volker" date="1329217409"]
The container classes, if filled with pointers, never call delete on that pointers once they are removed from the list or in case the list is emptied or destroyed. You must call delete yourself.[/quote]

Well, generally speaking this is true.

[quote author="stuk" date="1329208992"]... i haven't to delete anything in destructor.[/quote]

But one should add that in this particular case you probably need not to delete anything in the destructor, because the QRadioButton objects are automatically deleted as soon as parentWidget is deleted. So as long as parentWidget is deleted somewhen there is no need to call delete on the objects - they are deleted automatically due to Qts parent/child system.

goetz

Yes, that's true. Thanks for adding that clarification, Lukas. I was too focused on the container classes themselves.

stukdev

This topic become very interesting. Another question.
If i use QList and my radio button have parents but i set for my dialog a flag
@
setAttribute(Qt::WA_DeleteOnClose,true);
@
If i close the dialog radio buttons are deleted or not?
The parents is a QMainWindows so the parent is alive!

KA51O

if the parent of the radiobuttons is the dialog, the radiobuttons are deleted when the dialog is closed.
If the parent of the radiobuttons is the mainwindow but the buttons are only displayed in the dialog the buttons are finally deleted when the mainwindow is closed I think. I'm not sure about the effect of the attribute you set.

stukdev

I have a QMainWindow that open more dialog. I want create the dialog on a click and delete all its objects on a close button of that dialog for optimize memory.

KA51O

If you set the parent for all the elements displayed in the dialog correctly Qt will take care of the destruction of all the children of the dialog. So if your radiobuttons are displayed in the dialog and the dialog is set to be their parent you don't have to do anything with regard to destroying your buttons.

But if you want to reuse the buttons in another dialog you can of course set the mainwindow as their parent. This way you only need to create them once, store the pointers to them in your list and put them in every dialog you want. They should only finally be deleted when your mainwindow is closed. I haven't tried this myself so no guarantees that this is working.

Heres a "link to a thread":http://developer.qt.nokia.com/forums/viewthread/6646 which might also interest you.

goetz

Be aware: Once you put the radio buttons into a layout, the parentship of the the buttons is transferred to the layout's widget. So, if you create the buttons with QMainWindow as parent and put them into the layout contained somewhere in an independent QDialog, then the buttons are finally owned by that dialog or one of it's subwidgets!

stukdev

So i have this situation. Two class, one have a pointer to another class.

@
//Class base
class Base : public QDialog, private Ui::Base {
Q_OBJECT
public:
Base(QWidget *parent = 0);
~Base();
private:
Test *test;
};

Base::Base(QWidget *parent) : QDialog(parent)
{
setupUi(this);

test = new Test();

//Delete object after close
setAttribute(Qt::WA_DeleteOnClose);

}

Base::~Base()
{
//delete test //this crash if uncomment
}

//Test class
class Test
{
public:
Test();
~Test();
};

Test::Test()
{}

Test::~Test()
{
qDebug() << "death";
}
@

If i uncomment the line

@
delete test //this crash if uncomment
@

I see death in console but my app crash, otherwise if i comment the program don't crash but i don't see death and in top manager the memory is not free. What's the problem?

goetz

Run in a debugger and look where the crash occurs.

stukdev

If i run valgrind its say so that i've memory lost in
@
test = new Test();
@

So is correct use delete on descrutor? But i don't understand why my app crash for corrupted double-linked.

goetz

The code looks ok. I don't know what's going wrong here. Can you provide a complete test case?

stukdev

After hours i found the problem. The problem is a desctructor of QString. I have one class that load some string from a file and store it in a vector (now i can use a QList but this is old code). This vector is used by some class and is copy. In this old project there aren't delete and the program have much memory leak. The code is this:

@//Class that load string

class Loader
{
public:
Loader();
~Loader();
QString* getList();
private:
QString str[500];
};

Loader::Loader()
{
for(quint16 a=0;a<500;a++)
str[a] = "a"; //This is example fill str with 'a'
}

//This is another class that have loader class and call descructor
class Test : public QDialog, private Ui::Dprodotti {
Q_OBJECT
public:
Test(QWidget *parent = 0);
~Test();

private:
Loader *loader;
QString myStr[500];

private slots:
void on_pushButton_clicked();
};

Test::Test(QWidget *parent) : QDialog(parent)
{
setupUi(this);

loader = new Loader();
memcpy(myStr,product->getList(),sizeof(myStr));

setAttribute(Qt::WA_DeleteOnClose);

}

Test::~Test()
{
delete loader;
}

void Test::on_pushButton_clicked()
{
close();
}@

There something wrong in that QString vector but i don't understand what...

goetz

Use [[Doc:QStringList]] and get rid of memcopy and all the dangerous pointer stuff. It's not necessary here.