GTK_OBJECT was not declared in this scope when trying to transition to GTK3 (compile against gtk+-3.0 library)

Question

I am beginning with GTK development, and I have struggled.

This first application took me 4 hours, I would like to know now if I am already doing too many obvious mistakes?

Mainly I want to ask how do I transition this code to GTK3? It gives me error:

 ‘GTK_OBJECT’ was not declared in this scope

If I try to compile against GTK3 instead of GTK2, i.e.:

pkg-config --cflags --libs gtk+-3.0

---

#include <gtk/gtk.h>
static int click_counter = 0;
void greet ( GtkWidget * widget, gpointer data )
{
 g_print ( "My first GTK app!\n" );
 g_print ( "%s clicked %d times\n", (char*) data, ++click_counter );
}
void destroy ( GtkWidget * widget, gpointer data )
{
 gtk_main_quit ();
}
int main ( int argc, char * argv[] )
{
 GtkWidget * main_window;
 GtkWidget * counter_button;
 gtk_init( & argc, & argv);
 main_window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
 g_signal_connect (main_window, "destroy", G_CALLBACK (destroy), NULL);
 gtk_container_set_border_width ( GTK_CONTAINER ( main_window ), 30 );
 counter_button = gtk_button_new_with_label ("Click me!");
 g_signal_connect ( GTK_OBJECT(counter_button), "clicked", G_CALLBACK (greet), NULL ); // last param counter_button ?
 gtk_container_add ( GTK_CONTAINER (main_window), counter_button );
 gtk_widget_show_all ( main_window );
 gtk_main ();
 return 0;
}

---

I compile using a Makefile, the main part:

CXX := g++-8
CXXFLAGS := -std=c++17 -Wall -Wextra -Wc++11-compat # -Werror -Wpedantic -pedantic-errors
LDLIBS := $$( pkg-config --cflags --libs gtk+-2.0 )
PROJECT := firstGTK
BINARY := $(PROJECT)
SOURCE := $(PROJECT).cpp
$(BINARY): $(SOURCE)
 $(CXX) $(CXXFLAGS) $(SOURCE) -o $(BINARY) $(LDLIBS)

Answer 1

If you are porting GTK 2 code to GTK 3, then you should read the GTK 2 to 3 migration guide. It is to be expected that some changes to the code will be necessary when you switch.

There is a section that talks specifically about how to replace GtkObject. The answer is, in most cases, to use GObject or GtkWidget.

• Neil: The migration guide has been moved to here: developer-old.gnome.org/gtk3/stable/gtk-migrating-2-to-3.html