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| <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>, |
| and are already registered by GLib. |
| </p> |
| <p> |
| In the rare case of needing to register such a type in the type |
| system, fill a |
| <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> |
| <div class="informalexample"> |
| <table class="listing_frame" border="0" cellpadding="0" cellspacing="0"> |
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| <td class="listing_lines" align="right"><pre>1 |
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| 24</pre></td> |
| <td class="listing_code"><pre class="programlisting"><span class="usertype">GTypeInfo</span><span class="normal"> info </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span> |
| <span class="normal"> </span><span class="number">0</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* class_size */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* base_init */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* base_destroy */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* class_init */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* class_destroy */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* class_data */</span> |
| <span class="normal"> </span><span class="number">0</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* instance_size */</span> |
| <span class="normal"> </span><span class="number">0</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* n_preallocs */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* instance_init */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* value_table */</span> |
| <span class="cbracket">}</span><span class="symbol">;</span> |
| <span class="keyword">static</span><span class="normal"> </span><span class="keyword">const</span><span class="normal"> </span><span class="usertype">GTypeValueTable</span><span class="normal"> value_table </span><span class="symbol">=</span><span class="normal"> </span><span class="cbracket">{</span> |
| <span class="normal"> value_init_long0</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* value_init */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* value_free */</span> |
| <span class="normal"> value_copy_long0</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* value_copy */</span> |
| <span class="normal"> <a href="../glib-Standard-Macros.html#NULL:CAPS">NULL</a></span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* value_peek_pointer */</span> |
| <span class="normal"> </span><span class="string">"i"</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* collect_format */</span> |
| <span class="normal"> value_collect_int</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* collect_value */</span> |
| <span class="normal"> </span><span class="string">"p"</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* lcopy_format */</span> |
| <span class="normal"> value_lcopy_char</span><span class="symbol">,</span><span class="normal"> </span><span class="comment">/* lcopy_value */</span> |
| <span class="cbracket">}</span><span class="symbol">;</span> |
| <span class="normal">info</span><span class="symbol">.</span><span class="normal">value_table </span><span class="symbol">=</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">value_table</span><span class="symbol">;</span> |
| <span class="normal">type </span><span class="symbol">=</span><span class="normal"> </span><span class="function"><a href="gobject-Type-Information.html#g-type-register-fundamental">g_type_register_fundamental</a></span><span class="normal"> </span><span class="symbol">(</span><span class="normal"><a href="gobject-Type-Information.html#G-TYPE-CHAR:CAPS">G_TYPE_CHAR</a></span><span class="symbol">,</span><span class="normal"> </span><span class="string">"gchar"</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">info</span><span class="symbol">,</span><span class="normal"> </span><span class="symbol">&</span><span class="normal">finfo</span><span class="symbol">,</span><span class="normal"> </span><span class="number">0</span><span class="symbol">);</span></pre></td> |
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| </table> |
| </div> |
| |
| <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. |
| </p> |
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