Question

I wish to add items in a ListWidget, which is a private member of a class, through a friend function. Actually, i am trying this sample snippet to use friend function for more classes to update their ListWidgets from a single function.

I need guidance in using friend function in my case.

Kindly forgive my ignorance on the topic, any help is appreciated.

    class InBoxTab : public QWidget
    {
    Q_OBJECT

    public:
        InBoxTab(QWidget *parent = 0);
       // InBoxTab();
        ~InBoxTab();

    public slots:
        void hello();
        friend void adda(); // friend function
    private:
        QListWidget* listWidget1; //data member accessed by friend function
    };



    void adda()
    {
        InBoxTab I;

        I.listWidget1->insertItem(1,QString("added frm fn"));

        I.listWidget1->update();
    }


InBoxTab::InBoxTab(QWidget *parent) :
        QWidget(parent)
{
        listWidget1 = new QListWidget(this);

        QListWidgetItem* item = new QListWidgetItem("Item 1 added frm tab1 ");

        listWidget1->addItem(item);
        adda();   // Call to friend function

        QVBoxLayout* layout = new QVBoxLayout(this);
        layout->addWidget(listWidget1);
        this->setLayout(layout);
}

Answer 1

As far as I can see, the ‘adda’ function does not affect anything. It returns nothing, and only operates on ‘I’ which is deleted when ‘adda’ is finished.

An example of how I believe you could use a friend function would be if you declared/defined ‘adda’ as:

void adda(InBoxTab *I)
{
        I->listWidget1->insertItem(1,QString("added frm fn"));
        I->listWidget1->update();
}

… Although in that particular case there is no reason not to make ‘adda’ a member of the InBoxTab instead.