Passing function pointer

[kshegunov]

@CCRfan said in Passing function pointer:

Unfortunately, it don't want to work. I have got the following message

Could you post the code that generates that error - the function definition, the function declaration and the line where you get the pointer and use it?

[CCRfan]

I don't know why changed the forum engine this:
aka int (*)
to this:
aka int()
Should i use a formatting mechanism?

[kshegunov]

Yes, most certainly. See this thread.

[CCRfan]

The name of the function what i would like pass is: buttonClicked
Important part from the class header file, with function declaration:

class A8GS_Widget : public QWidget
{
    Q_OBJECT
public:
    explicit A8GS_Widget(QWidget *parent = 0);
    ~A8GS_Widget();
    LPDIRECT3D9 m_pD3D;
    LPDIRECT3DDEVICE9 m_pd3dDevice;
    ENGINE_VARS *ev;
    void A8GS_start();
    EVENT ShowKey(var _ScanCode);
    void buttonClicked(int, PANEL *);
    QWidget *A8GS_Widget_parent;
    bool A8GS_init_stop;

signals:

public slots:
    void engineStart();
    void engineClose();
    void engineBoxSign();
};

typedef void (*ButtonClickType)(int, PANEL *);
ButtonClickType pointerToFunction = &A8GS_Widget::buttonClicked;

Important part 1 from the cpp file, the function definition:

void A8GS_Widget::buttonClicked(int buttonId, PANEL *panelId) {
    qDebug() << "buttonClicked";
    qDebug() << buttonId;
}

Important part 2 from the cpp file, where i want to pass the function as parameter:

void A8GS_Widget::A8GS_start() {
...
    pan_setbutton(pan_ize, 0, 0, 104, 226, bmap_1, bmap_1, bmap_1, NULL, (void *)(&A8GS_Widget::buttonClicked), NULL, NULL);
...

I hope i didn't miss nothing.

[kshegunov]

It won't work like this. Remember I wrote that static functions can be passed as global functions (C-like functions). Methods (like buttonClicked) have to be bound to an object, which is problematic in your case, because pan_setbutton expect a C-style function, not a class method.

[CCRfan]

@kshegunov said in Passing function pointer:

It won't work like this. Remember I wrote that static functions can be passed as global functions (C-like functions). Methods (like buttonClicked) have to be bound to an object, which is problematic in your case, because pan_setbutton expect a C-style function, not a class method.

OK, and how will work?
If you can see any possible changes, let me share, and i can continue my work. I started to use this Qt tool since one month and i really, really like.
I would appreciate any good proposal.
Thanks in advance.

[kshegunov]

There aren't really good solutions for that one, that's why I was reluctant to propose anything. Your best bet is to use a global pointer to pass the context. Something like this:

class A8GS_Widget : public QWidget
{
    Q_OBJECT

    // ...
    static void panSetButton(int, PANEL *);

private:
    static A8GS_Widget * currentWidget;
};   

And then in the .cpp:

A8GS_Widget * A8GS_Widget::currentWidget = Q_NULLPTR;

void A8GS_Widget::panSetButton(int id, PANEL * panelId)
{
    Q_ASSERT(currentWidget);
    currentWidget->buttonClicked(id, panelId)
}

void A8GS_Widget::A8GS_start()
{
    // ...
    currentWidget = this;
    pan_setbutton(pan_ize, 0, 0, 104, 226, bmap_1, bmap_1, bmap_1, NULL, &A8GS_Widget::panSetButton, NULL, NULL);
    // ...
}

It's not ideal, but it's how this problem is treated most commonly.

[CCRfan]

Thank for your will to help.
I feel myself lucky, because i started another way to solve the problem. It seems to me works.
I have made the following changes:

1. I added static prefix tag to the function declaration, because i forgot to that earlier
2. I moved the following statement from the header to the cpp as the first line of the void A8GS_Widget::A8GS_start()

ButtonClickType pointerToFunction = &A8GS_Widget::buttonClicked;

3. I changed the definition here:

void A8GS_Widget::buttonClicked(int buttonId, PANEL *panelId)

from int buttonId, to var buttonId.
And it works! I like it!
Only one problem remained, i got 1024 as buttonId that should be 1. I think this is my deal with the engine.
Thanks for the quick and kind help.
I am investigate a bit more, and later i set to solved this topic.

[CCRfan]

@kshegunov Thank for the real quick and expert help.
I am happy with that.

[kshegunov]

I'm glad I was of help. Happy coding!