Re: C++-classes.

[James Durie <jdurie anvil co uk>]

On Fri, 2002-10-18 at 10:55, Peeter Vois wrote:
> On 18 Oct 2002 09:35:06 +0100
> James Durie <jdurie anvil co uk> wrote:
>
> > You can't pass a method in as a callback function pointer. There is a
> > hidden parameter, this, to all methods which points to the instance of
> > the class.
> >
> > Instead try:
> > gtk_signal_connect(GTK_OBJECT(button), "clicked",
> > GTK_SIGNAL_FUNC(clicked_cb), this);
>
> I would like to say that I never used GTK with C++ before but does not following
> work? Or something like this:
>
> gtk_signal_connect(GTK_OBJECT(button), "clicked",
>       GTK_SIGNAL_FUNC(this->Test), NULL);

That would imply that a separate instance of each method of the class is
created whenever an instance of the class is created. Which would be
incredibly wasteful of memory. Instead a single instance of each method
is created and a hidden parameter is passed to the method whenever it is
called. C++ hides the details of this from you.

So passing the address of method Test as a function pointer would not
work because the method would have no idea which instance of the class
it is working on.

James

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