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A lot of types are not instantiatable 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:
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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-instantiatable 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.