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Re: THISBACK and inheritance [message #48481 is a reply to message #48475]

Thu, 06 July 2017 20:25

Oblivion
Messages: 1093
Registered: August 2007

Senior Contributor

Hello,

It is a "C++ thing." Smile

As far as I can see, you are calling a pure virtual method (or storing its address -which is undefined at that moment) from base constructor.
Calling a pure virtual method from base constructor is undefined behaviour. (Since at that point the vtable entry for the said method is not yet assigned. It is basically "0" (undefined)). That's why you dont't even get an explicit error message.

MenuBarWindow::MenuBarWindow(int _sizeX, int _sizeY)
{
    SetRect(0, 0, Zx(_sizeX), Zy(_sizeY + m_menuBar.GetStdHeight(m_menuBar.GetFont())));
    AddFrame(m_menuBar);
    m_menuBar.Set(THISBACK(MenuBarMain)); // <-- Undefined behaviour.
}

Why did you define a menu handler virtual anyway? We are using callbacks to define menus, so you won't really need virtual functions for this purpose.
if you want to store m_menuBar member in MenuBarWindow class that's fine, but since it is a protected member, it can be accessed from the derived classes:

MyWindow::MyWindow(int _sizeX, int _sizeY)
    : FnWindow(_sizeX, _sizeY)
{
        AddFrame(m_menuBar);                             // This should
	m_menuBar.Set(THISBACK(MenuBarMain));            // work.
}

Also I see that you use some obscure internal macro(s) explicitly. You dont need them at all.

Best regards,
Oblivion

Github page: https://github.com/ismail-yilmaz
upp-components: https://github.com/ismail-yilmaz/upp-components
Bobcat the terminal emulator: https://github.com/ismail-yilmaz/Bobcat

[Updated on: Thu, 06 July 2017 21:07]

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