Can't Understand Weird C Runtime Error. Need Help?

I am trying to master the GObject Library. So I tried to make a simple Gtk+ Custom Widget by inheriting from GtkHBox. I can't figure out what the problem is or even where the problem is so I'll have to paste the entire code. Here is the code:

notetab.h

#ifndef NOTETAB_H
#define NOTETAB_H

G_BEGIN_DECLS

#define PRO_NOTE_TAB(obj) GTK_CHECK_CAST(obj, pro_note_tab_get_type (), ProNoteTab)
#define GTK_CPU_CLASS(klass) GTK_CHECK_CLASS_CAST(klass, pro_note_tab_get_type(), ProNoteTabClass)
#define GTK_IS_CPU(obj) GTK_CHECK_TYPE(obj, pro_note_tab_get_type())

typedef struct _ProNoteTab ProNoteTab;
typedef struct _ProNoteTabClass ProNoteTabClass;

struct _ProNoteTab
{
    GtkWidget hbox;
    GtkObject parent_instance;
    GtkLabel label;
    GtkButton cbtn;
};

struct _ProNoteTabClass
{
    GtkHBoxClass parent_class;
};

GtkType pro_note_tab_get_type(void);
GtkWidget* pro_note_tab_new(void);

G_END_DECLS

#endif

notetab.c

#include "common.h"
#include "notetab.h"

GtkType pro_note_tab开发者_运维技巧_get_type()
{
    GtkType pro_note_tab_type = 0;

    if (!pro_note_tab_get_type)
    {
        static const GtkTypeInfo pro_note_tab_info =
        {
            "ProNoteTab",
            sizeof(ProNoteTab),
            sizeof(ProNoteTabClass),
            (GtkClassInitFunc) NULL,
            (GtkObjectInitFunc) NULL,
            NULL,
            NULL,
            (GtkClassInitFunc) NULL
        };

        pro_note_tab_type = gtk_type_unique(GTK_TYPE_WIDGET, &pro_note_tab_info);
    }

    return pro_note_tab_type;
}

GtkWidget* pro_note_tab_new(void)
{
    return GTK_WIDGET(gtk_type_new(pro_note_tab_get_type()));
}

Now the program compiles perfectly fine. But the error I get at runtime is:

GTK_CRITICAL**: IA__gtk_type_new : assertion GTK_TYPE_IS_OBJECT(type) failed GTK_CRITICAL**: IA__gtk_container_add : assertion GTK_IS_WIDGET(widget) failed

What am I doing wrong? Or even I what in the world is this error about?

According to the docs, gtk_type_unique is "deprecated and should not be used in newly-written code".

Use g_type_register_static instead. More so if you are trying to master GObject, not old Gtk+.

Anyway, I'd say that your error is due to some of the NULL function pointers you are setting, some are probably not optional, but this is poorly documented.

For one, the pro_note_tab_type variable in pro_note_tab_get_type() really looks like it should be static.

That must be the problem

 if (!pro_note_tab_get_type)
{