manpagez: man pages & more
html files: gobject
Home | html | info | man

Non-instantiable non-classed fundamental types

A lot of types are not instantiable by the type system and do not have a class. Most of these types are fundamental trivial types such as gchar, and are already registered by GLib.

In the rare case of needing to register such a type in the type system, fill a GTypeInfo structure with zeros since these types are also most of the time fundamental:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
GTypeInfo info = {
  0,                                /* class_size */
  NULL,                        /* base_init */
  NULL,                        /* base_destroy */
  NULL,                        /* class_init */
  NULL,                        /* class_destroy */
  NULL,                        /* class_data */
  0,                                /* instance_size */
  0,                                /* n_preallocs */
  NULL,                        /* instance_init */
  NULL,                        /* value_table */
};
static const GTypeValueTable value_table = {
  value_init_long0,                /* value_init */
  NULL,                        /* value_free */
  value_copy_long0,                /* value_copy */
  NULL,                        /* value_peek_pointer */
  "i",                        /* collect_format */
  value_collect_int,        /* collect_value */
  "p",                        /* lcopy_format */
  value_lcopy_char,                /* lcopy_value */
};
info.value_table = &value_table;
type = g_type_register_fundamental (G_TYPE_CHAR, "gchar", &info, &finfo, 0);

Having non-instantiable types might seem a bit useless: what good is a type if you cannot instantiate an instance of that type ? Most of these types are used in conjunction with GValues: a GValue is initialized with an integer or a string and it is passed around by using the registered type's value_table. GValues (and by extension these trivial fundamental types) are most useful when used in conjunction with object properties and signals.

© manpagez.com 2000-2017
Individual documents may contain additional copyright information.