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, registered in g_value_types_init (in gvaluetypes.c).
在类型系统中，许多类型是不可实例化而且没有父类的。大多数这些类型是最基础的基本类型，如 gchar，它由 g_value_types_init 注册（在gvaluetypes.c中）。
To register such a type in the type system, you just need to fill the GTypeInfo structure with zeros since these types are also most of the time fundamental:
如果想在类型系统中注册这样一个类型，你仅仅需要用 0 来填充 GTypeInfo 结构。
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.
使用不可实例的类型似乎是无用的：定义一个不能实例化的类型有什么好处呢？大多数这种类型与 GValue 用作一块：一个 GValue 由一个整型或一个字符串来初始化，再被传递了一个已注册类型的 value_table 。GValue（以基本类型延伸）最有用的时候是在与对象的属性和信号用在一块时。