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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-memory-shared-resources"></a>Shared resources</h2></div></div></div>
<p>
Some objects, such as <code class="classname">Gdk::Pixbuf</code>s and
<code class="classname">Pango::Font</code>s, are obtained from a shared store.
Therefore you cannot instantiate your own instances. These classes typically
inherit from <code class="classname">Glib::Object</code>. Rather than requiring you to
reference and unreference these objects, <span class="application">gtkmm</span> uses the
<code class="classname">Glib::RefPtr<></code> smartpointer. Cairomm has its own
smartpointer, <code class="classname">Cairo::RefPtr<></code>.
</p>
<p>
Objects such as <code class="classname">Gdk::Pixbuf</code> can only be instantiated
with a <code class="methodname">create()</code> function. For instance,
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<pre class="programlisting">
Glib::RefPtr<Gdk::Pixbuf> pixbuf = Gdk::Pixbuf::create_from_file(filename);
</pre>
<p>
</p>
<p>
You have no way of getting a bare <code class="classname">Gdk::Pixbuf</code>. In the
example, <code class="varname">pixbuf</code> is a smart pointer, so you can do this, much
like a normal pointer:
</p>
<pre class="programlisting">
int width = 0;
if(pixbuf)
{
width = pixbuf->get_width();
}
</pre>
<p>
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<p>
When <code class="varname">pixbuf</code> goes out of scope an
<code class="methodname">unref()</code> will happen in the background and you don't need
to worry about it anymore. There's no <code class="literal">new</code> so there's no
<code class="literal">delete</code>.
</p>
<p>
If you copy a <code class="classname">RefPtr</code>, for instance
</p>
<pre class="programlisting">
Glib::RefPtr<Gdk::Pixbuf> pixbuf2 = pixbuf;
</pre>
<p>
, or if you pass it as a method argument or a return type, then
<code class="classname">RefPtr</code> will do any necessary referencing to ensure that
the instance will not be destroyed until the last <code class="classname">RefPtr</code>
has gone out of scope.
</p>
<p>See the <a class="link" href="chapter-refptr.html" title="Appendix A. The RefPtr smartpointer">appendix</a> for detailed information about RefPtr.</p>
<p>
If you wish to learn more about smartpointers, you might look in these
books:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
Bjarne Stroustrup, "The C++ Programming Language" Forth Edition - section 34.3
</p></li>
<li class="listitem"><p>
Nicolai M. Josuttis, "The C++ Standard Library" - section 4.2
</p></li>
</ul></div>
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