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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-basics-gobj-and-wrap"></a>Mixing C and C++ APIs</h2></div></div></div>
<p>You can use C APIs which do not yet have convenient C++ interfaces.
It is generally not a problem to use C APIs from C++, and <span class="application">gtkmm</span> helps by
providing access to the underlying C object, and providing an easy way to create
a C++ wrapper object from a C object, provided that the C API is also based on
the <code class="classname">GObject</code> system.</p>
<p>
To use a <span class="application">gtkmm</span> instance with a C function that requires a C
<code class="classname">GObject</code> instance, use the C++ instance’s
<code class="function">gobj()</code> function to obtain a pointer to the underlying C
instance. For example:
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<pre class="programlisting">
Gtk::Button* button = new Gtk::Button("example");
gtk_button_do_something_that_gtkmm_cannot(button->gobj());
</pre>
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</p>
<p>
To obtain a <span class="application">gtkmm</span> instance from a C <code class="classname">GObject</code> instance,
use one of the many overloaded <code class="function">Glib::wrap()</code> functions.
The C instance’s reference count is not incremented, unless you set the optional
<em class="parameter"><code>take_copy</code></em> argument to <code class="literal">true</code>. For
example:
</p>
<pre class="programlisting">
GtkButton* cbutton = get_a_button();
Gtk::Button* button = Glib::wrap(cbutton);
button->set_label("Now I speak C++ too!");
</pre>
<p>
The C++ wrapper shall be explicitly deleted if
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>it's a widget or other class that inherits from <code class="classname">Gtk::Object</code>, and</p></li>
<li class="listitem"><p>the C instance has a floating reference when the wrapper is created, and</p></li>
<li class="listitem"><p><code class="function">Gtk::manage()</code> has not been called on it (which includes if it was created with <code class="function">Gtk::make_managed()</code>), or</p></li>
<li class="listitem"><p><code class="function">Gtk::manage()</code> was called on it, but it was never added to, or was later removed from, its parent.</p></li>
</ul></div>
<p>
<code class="function">Glib::wrap()</code> binds the C and C++ instances to each other.
Don't delete the C++ instance before you want the C instance to die.
</p>
<p>In all other cases the C++ instance is automatically deleted when the last reference
to the C instance is dropped. This includes all <code class="function">Glib::wrap()</code>
overloads that return a <code class="classname">Glib::RefPtr</code>.</p>
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