toshiocp / gobject-tutorial Goto Github PK

Hello! First and foremost thanks for the tutorial you've made, it's helping me to understand how to use the GObject library (and how it works).

I tried running the second example in section 2 locally, and ran into an SIGSEGV (Address boundary error).

#include <glib-object.h>

static void
show_ref_count (GObject *instance) {
  if (G_IS_OBJECT (instance))
    /* Users should not use ref_count member in their program. */
    /* This is only for demonstration. */
    g_print ("Reference count is %d.\n", instance->ref_count);
  else
    g_print ("Instance is not GObject.\n");
}

int
main (int argc, char **argv) {
  GObject *instance;
  
  instance = g_object_new (G_TYPE_OBJECT, NULL);
  g_print ("Call g_object_new.\n");
  show_ref_count (instance);
  g_object_ref (instance);
  g_print ("Call g_object_ref.\n");
  show_ref_count (instance);
  g_object_unref (instance);
  g_print ("Call g_object_unref.\n");
  show_ref_count (instance);
  g_object_unref (instance);
  g_print ("Call g_object_unref.\n");
  show_ref_count (instance);
  
  return 0;
}

I've used gdb and the problem is at the last line show_ref_count (instance) after the instance has been freed. It doesn't even get into the function show_ref_count nor the G_IS_OBJECT call, it fails before at g_type_check_instance_is_fundamentally_a which I would guess happens when the instance pointer is copied into a function? 🤔 I'm not sure how that happens.

I don't know either if it's any problem with my local environment. In your page you mention that there are examples in the misc folder, but I couldn't find those here.

I'm using an Arch Linux and compiling via gcc with the following command:

gcc -g example.c -o example $(pkg-config --cflags --libs gobject-2.0)

If it is the case that my environment is correct and this error is reproducible, how does one check that an GObject * instance is null without calling any function using it? 🤔

https://github.com/ToshioCP/Gobject-tutorial/blob/main/gfm/sec6.md?plain=1#L39

When an instance is TNumber type, it is an instance of TInt or TDouble as well.

should be

When an instance is of TInt or TDouble type, it is an instance of TNumber as well.

btw. I appreciate your work! IMHO, It's way better organized than gobject's official guide.

https://github.com/ToshioCP/Gobject-tutorial/blob/main/gfm/sec4.md?plain=1#L104
https://github.com/ToshioCP/Gobject-tutorial/blob/main/gfm/sec4.md?plain=1#L110

void dev_by_zero_cb (TDouble *d, gpointer user_data) { ... ... ...};

and

void dev_by_zero_cb (TDouble *d) { ... ... ...};

should be

void div_by_zero_cb (TDouble *d, gpointer user_data) { ... ... ...};

and

void div_by_zero_cb (TDouble *d) { ... ... ...};

The documentation seems to only talk about how to use GObject and not what it is used for. It is a simple thing that demands research from casual readers trying to find footing. Two sentences should be sufficient.