Re: GTK2 with c++, without gtkmm

[Jeff Franks <jcf tpg com au>]

Progss wrote:
> Hi all!
>
> I've been just a reader of this mailing-group, but it seems to me, that
> now I've got a problem which cannot be solved just after reading :)
>
> I'm writing an application using GTK2, however I decided to use
> C++ because of it's objects :) I tried not to pay attention to some
> difficulties, but they return. Type matching is too strict, so after e.g:
>
> [cut]
>     hsep = gtk_hseparator_new();
>     gtk_table_attach(GTK_TABLE(packTable), hsep , 0,2,2,3,
>                                 GTK_FILL|GTK_SHRINK, GTK_FILL, // *** HERE!
>                                 0,0 );
> [cut]
>
> error message is like that:
> ---
> cannot convert `int' to `GtkAttachOptions' for argument
> `7' to `gtk_table_attach (GtkTable *, GtkWidget *, unsigned int, unsigned
> int, unsigned int, unsigned
> int, GtkAttachOptions, GtkAttachOptions, unsigned int, unsigned int)'
> ---

Unlike C, C++ wont let you assign OR'd bit values to an enum, you have 
to do a cast, like so:

...
(GtkAttachOptions)GTK_FILL|GTK_SHRINK,
...

> There are also problems when try to call  g_signal_connect()
> passing a static class method as a callback function.
>
> I'm using "gpointer data" to pass extra data, because
> in a static function I cannot access non-static class members.
>
> SOMETHING LIKE AN EXAMPLE:
>
> class Foo {
> public:
>     GtkWidget* button;
>     static void callback(GtkWidget* widget, gpointer data);
>     gint foo2;
> };
>
> [,,,]   g_signal_connect (G_OBJECT (button), "clicked",
>                     G_CALLBACK (callback), (gpointer) this->foo2);

this->foo2 is a copy of foo2, (a temporary value), not the address of 
foo2. So you can only read the value passed. You can't assign a value to 
it.

> void Foo::callback(GtkWidget* widget, gpointer data
>     (gint) data=5;
> [...] }

You can't do this:

(gint) data=5;

You are trying to assign a value to a temporary value for use outside 
the function.

> ... does not work - I got an errortrying to access foo2
> - "invalid use of member in static member function"
>
> works only:
> [,,,]   g_signal_connect (G_OBJECT (button), "clicked",
>                     G_CALLBACK (callback), (gpointer) this);
> and then:
> [...] ((Foo*)this)->foo2 = 5;
>
> Is there a way to solve those problem?
> Or does anyone see where I made my mistakes?

This is correct:

((Foo*)this)->foo2 = 5;

You have to assign a value to this->foo2 through the pointer passed in 
data.


> Thanks,
> Waldek Maleska
>
>
> ----------------------------------------------------------------------
> Zostan trenerem kadry skoczkow i wygraj bilet pod skocznie!
>
> > > > http://link.interia.pl/f16a5 
>
>
>
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