Re: Casting GtkWidgets

[Jeroen Benckhuijsen <jfbenck home nl>]

On Thu, 05 Oct 2000 01:05:17 Willem Robert van Hage wrote:
> Naheed Vora wrote:
> > void
> > on_combo_entry1_activate               (GtkEditable     *editable,
> >                                         gpointer         user_data)
> > {
> >
> > GtkWidget *text_entry = user_data;
> > char *string = gtk_entry_get_text(GTK_ENTRY (text_entry));
> > g_print(string);
> >
> > }
>
> this should be:
>
> void on_combo_entry1_activate(GtkEditable *editable,gpointer user_data)
> {
>   gchar *string = gtk_entry_get_text(GTK_ENTRY(user_data));
>   g_print(string);
> }
>
> or:
>
> void on_combo_entry1_activate(GtkEditable *editable,gpointer user_data)
> {
>   GtkWidget *entry = GTK_WIDGET(user_data);
>   gchar *string = gtk_entry_get_text(GTK_ENTRY(entry));
>   g_print(string);
> }
>
> or:
>
> void on_combo_entry1_activate(GtkEditable *editable,gpointer user_data)
> {
>   GtkWidget *entry = (GtkWidget*)user_data;
>   gchar *string = gtk_entry_get_text(GTK_ENTRY(entry));
>   g_print(string);
> }
>
>
> that all does the same...
>
> > Gtk-WARNING **: invalid cast from (NULL) pointer to `GtkEntry'
>
> that's true, because a gpointer is really a void*, and you can't
> reference a pointer to something of type void.

Ahum, this is not true, it says there's an invalid cast, not a reference,
He just saying something like:

entry = (GtkWidget*)user_data, where user_data == NULL. The GTK_WIDGET
macro checks this , and displays the error message shown

You're right you can't refenence are void*, however this is not being done
here. (The * is within the (), so it's just a cast from void* (the
gpointer) to GtkWidget*, just another pointer.

Also in the Gtk Api reference one can read that gtk_entry_get_text is
deprecated. gtk_editable_get_chars schould be used instead.

Jeroen