Class TypeClass

When an object is allocated, the private structures for the type and all of its parent types are allocated sequentially in the same memory block as the public structures, and are zero-filled.

Note that the accumulated size of the private structures of a type and all its parent types cannot exceed 64 KiB.

This function should be called in the type's class_init() function. The private structure can be retrieved using the G_TYPE_INSTANCE_GET_PRIVATE() macro.

The following example shows attaching a private structure MyObjectPrivate to an object MyObject defined in the standard GObject fashion in the type's class_init() function.

Note the use of a structure member "priv" to avoid the overhead of repeatedly calling MY_OBJECT_GET_PRIVATE().

typedef struct _MyObject        MyObject;
typedef struct _MyObjectPrivate MyObjectPrivate;

struct _MyObject {
 GObject parent;

 MyObjectPrivate *priv;
};

struct _MyObjectPrivate {
  int some_field;
};

static void
my_object_class_init (MyObjectClass *klass)
{
  g_type_class_add_private (klass, sizeof (MyObjectPrivate));
}

static void
my_object_init (MyObject *my_object)
{
  my_object->priv = G_TYPE_INSTANCE_GET_PRIVATE (my_object,
                                                 MY_TYPE_OBJECT,
                                                 MyObjectPrivate);
  // my_object->priv->some_field will be automatically initialised to 0
}

static int
my_object_get_some_field (MyObject *my_object)
{
  MyObjectPrivate *priv;

  g_return_val_if_fail (MY_IS_OBJECT (my_object), 0);

  priv = my_object->priv;

  return priv->some_field;
}

This function is essentially equivalent to: g_type_class_peek (g_type_parent (G_TYPE_FROM_CLASS (g_class)))