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<title>Non-instantiable non-classed fundamental types</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="gtype-non-instantiable"></a>Non-instantiable non-classed fundamental types</h2></div></div></div>
<p>
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 <span class="emphasis"><em>gchar</em></span>,
registered in <code class="function">_g_value_types_init</code> (in <code class="filename">gvaluetypes.c</code>).
</p>
<p>
To register such a type in the type system, you just need to fill the
<a class="link" href="gobject-Type-Information.html#GTypeInfo" title="struct GTypeInfo"><span class="type">GTypeInfo</span></a> structure with zeros since these types are also most of the time
fundamental:
</p>
<pre class="programlisting">
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);
</pre>
<p>
</p>
<p>
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 <a class="link" href="gobject-Generic-values.html#GValue" title="GValue"><span class="type">GValue</span></a>s: a GValue is initialized
with an integer or a string and it is passed around by using the registered
type's value_table. <a class="link" href="gobject-Generic-values.html#GValue" title="GValue"><span class="type">GValue</span></a>s (and by extension these trivial fundamental
types) are most useful when used in conjunction with object properties and signals.
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