Boilerplate code

In your code, the first step is to #include the needed headers: depending on your header include strategy, this can be as simple as #include "maman-bar.h" or as complicated as tens of #include lines ending with #include "maman-bar.h":

/*
 * Copyright information
 */

#include "maman-bar.h"

/* If you use Pimpls, include the private structure 
 * definition here. Some people create a maman-bar-private.h header
 * which is included by the maman-bar.c file and which contains the
 * definition for this private structure.
 */
struct _MamanBarPrivate {
  int member_1;
  /* stuff */
};

/* 
 * forward definitions
 */

Call the G_DEFINE_TYPE macro using the name of the type, the prefix of the functions and the parent GType to reduce the amount of boilerplate needed. This macro will:

implement the maman_bar_get_type function
define a parent class pointer accessible from the whole .c file

G_DEFINE_TYPE (MamanBar, maman_bar, G_TYPE_OBJECT);

It is also possible to use the G_DEFINE_TYPE_WITH_CODE macro to control the get_type function implementation - for instance, to add a call to G_IMPLEMENT_INTERFACE macro which will call the g_type_implement_interface function.